[Closed] New boiler time - to combi or not

Appeared without a bump - is it fixed now?

I might be old fashioned but I like having a tank of hot water!
I can't help but feel that short cycling a boiler just to make a little hot water multiple times a day can't be good for the boilers longevity.
You've got all the pipework in place for a tank.... May as well use it.
Fairly big house? - tank.
You also have the option to upgrade to an unvented system (if it's not already) and get great pressure throughout the house.

We have a large-ish 4 bed house and a combi-boiler. Only three of us mind and one of them is still but a bairn. Wouldn't be doing with tanks and stuff, they just seem like hard work. I could be completely mis-guided but just knowing the water will definitely be hot whenever we need it works for us and it's never been an issue with using the shower etc

Appeared without a bump – is it fixed now?

It's been fixed for ages but no one seemed to notice.

I'm considering this question right now.

We have an ageing unvented system which will need replacement at some point in the near future. If we can take the cylinder out of the equation, we can in theory extend the bathroom into the airing cupboard to make room for a proper shower cubicle.

The issue is whether a decent make of combi can ever compete with (or get close to) an unvented system in terms of shower pressure etc.

Out last house had a combi- great to have hot water on tap, but when it goes wrong you have no hot water and no heating as happened to us. Current house has tank & boiler- when we replaced the system there was no way I would go for a combi after the hassle in the old house.

We recently replaced our 20year old combi with a new one. The old one had only ever been serviced once or twice and never broke down. We only replaced it as we needed to move it anyway so it seemed a sensible time. We had a option of a tank but I couldn't find a good reason to do so.

We can run two showers at the same time, pressure is good and not having a tank keeps space free for other stuff. We have a spare shower downstairs used for cleaning the dog or stepping into after stripping off muddy biking / rugby / football gear. We put an electric shower in there so we still have hot water if the boiler fails (as these things only ever happen on Christmas eve). It could also be used as a third running shower at the same time but I struggle to think of a reason why we would do so.

We are using a worcester bosch greenstar.

The issue is whether a decent make of combi can ever compete with (or get close to) an unvented system in terms of shower pressure etc.

We have really good shower pressure with our combi and no need for an additional pump or anything. Works just grand 🙂

I'll admit to being swung by a combi that's been trouble for a while now and now is awaiting replacement after less than what I'd consider a reasonable life, however I'm sick of the shower going ice cold half way through!

I'm sure that the same is true to some extent of modern non-combi boilers, but they appear to be overly fragile and having so much packed into one box makes them complicated meaning that repairs are expensive.

It'll be somewhat reluctantly replaced with another combi though. Replumbing back to a tank based system is pricy and I suspect would impact the desirability of a smaller house. I'd not be switching another house to a combi given a free choice, though.

Combi here and it works just fine - no way would I go back to a hot water cylinder!

Our Worcester Bosch one is 13 years old and has never been serviced or broken down.

Go for a Worcester Bosch or Vaillant and it will be fine. Go for a cheap one and you'll have years of pain - the Vokera one we have at work is shite.

If it were me I'd be looking at heat pumps, there are bound to be some govt money back schemes so could work out evens

https://www.worcester-bosch.co.uk/products/heat-pumps

Used to have a boiler in the kitchen, hot water tank in an airing cupboard upstairs and cold water tank in the loft, when re did the kitchen put an Ideal Vogue combi with 12 year warranty in the loft to free up space in the kitchen, pipe work already up and down from the loft so didn't take much plumbing in, have an external gas meter so pipe for gas goes straight up outside of house.

Had an issue with the wireless room stat and Ideal attended and swapped it for the new shiny,smart one for free.

Wouldn’t be doing with tanks and stuff, they just seem like hard work.

Really?
Just what "work" is involved?
.... Oh wait.... None!

And as an addition - if solar is ever put on the house then it will heat your hot water using the immersion for over 6 months of the year.

We had a combi at our last house and I hated it - the water pressure at the shower head would fluctuate wildly if any water was used elsewhere in the house. When we moved into our current house nine years ago (and with two little girls at the time) we installed a mains pressure unvented system. It is the best thing ever - those two little girls are now 12 and showering regularly and whilst there is a slight drop in pressure, it is still very powerful. And if the hot water is switched on it heats almost as fast as it is being used so we can comfortably have four decent showers in a row (that's with two showers being used concurrently).

And OP - rather than a small radiator in the airing cupboard you could use a greenhouse heater teamed up with a plug-in socket thermostat. That's what we have and it keeps our airing cupboard nicely warm - and cost pennies to run.

Go for a Worcester Bosch or Vaillant and it will be fine.

FWIW, it's a Worcester Bosch that's given me trouble. I appreciate that I've been unlucky, but it's not unheard of to be replacing the boiler at this age from talking to my plumber.

Do you know what? I would say no. Literally just had BG out again today to change a leaking flow valve. We had a pin holed manifold in March both of which caused leaks down through the kitchen ceiling. This is a 9 year old Worcester Bosch Combi which we had fitted when we moved in. Before it was a 1980's back boiler and immersion. In hindsight I would have just updated the open system and got a new hot water tank.

Good question & it's interesting to hear the answers as we are currently looking at replacing our boiler & I am really not sure what is for the best.

We currently have what I would call an 'old school' system. I don't know the exact name for it, but it's basically a normal boiler that does the heating & hot water, with a tank in the airing cupboard.

I am torn between keeping the system as it is & replacing the boiler for the same type, or going for a combi.
We had a couple of boiler issues over the winter & having the ability to flick the immersion on was a god-send; especially when we were told it could be 3 weeks before anyone could get to look at it.
We also have an electric shower, so no issues there.

I am unsure whether to get a combi, so we could get rid of the tank & possibly having the boiler moved into the airing cupboard although not sure if that would be too noisy....? Alternatively, we could potentially have the boiler moved to the garage, which is attached to the house.
We would ideally move it to free up space in the kitchen.

I'd also get piping added at the same time to run hot water to the bathroom for an easy swap from the electric shower when we finally re-do the bathroom. I figure having it put in at the time of installing the new boiler would be cheaper than having it done at a later date, even if we decide not to use it.

Alternatively, we could potentially have the boiler moved to the garage, which is attached to the house. We would ideally move it to free up space in the kitchen.

We did that - the boiler was in the garage but the hot water tank was in the main bathroom with the header talk in the loft (a pretty normal set-up). We decommissioned the header tank and installed the new hot water tank with immersion in the garage next to the boiler and the valves/headers/regulators or whatever they are for the unvented system. We then removed all the boxing in for the hot water tank from the bathroom when we did a refit - it makes it a much bigger space.

One last thing - get the biggest hot water tank you can - they keep water hot for a long time and it's nice to have acsess to lots of hot water. I am not sure what the volume is of ours, but it's almost 6ft tall!

I think I'll have a bath. *puts the hot water on and waits 20 minutes*

Oh, I've run out of hot water.

@Cougar - yep, that nails it...

Cougar - it would help if you said which boiler you have!

Fwiw, we have an electric shower, and no option to move boiler into the loft, so it needs to stay where it is.

Keep the answers coming

The airing cupboard is handy storage, the immersion heater in the tank has been useful once or twice when the boiler has broken, so not desperate to get rid of it.

I think its odd to spec a heating system on the basis that it's going to fail often enough for that to matter, v's the inconvenience of boiling some kettles. Of course, it may be you have so much space you won't notice the extra storage.

I suppose the question could be - will ground/air source heat pumps require a (the same?) tank, and therefore are you ripping out something you will have to replace in 15 years. On the other hand 15 years is a long time to put up with an unnecessary tank.

I’d also get piping added at the same time to run hot water to the bathroom for an easy swap from the electric shower when we finally re-do the bathroom.

On the contraty, If you get a combi then I'd retain the electric shower. All boilers are susceptible to breaking down. they just do. It's the only bit both systems have in common so equally susceptible. So when the boiler breaks down with a combi you're screwed so the electric shower will come in handy. With a storage system you can still heat up a tank of hot water in under 15 minutes.

And never had issues with running out of hot water. I share a home with 3 women and all four of us can have a shower without running the tank empty of hot water. OK its a functional shower so no lounging around in a Turkish bath of a steaming shower...but if its first thing in the morning with everyone getting ready for work and school (even less of an issue now the wife and I work from home), or we're all getting ready to go out then that is not the time to have a long shower anyway combi or no combi.

I think if its just two of you, or maybe 3 then combi all the way because the volume of hot water consumption is smaller. But for a larger family then storage is the way I'd go.

Cougar – it would help if you said which boiler you have!

In the old house I had a 40+ year old system. Gas fire, back boiler, hot water tank, cold tank in the loft, pump that wouldn't have looked out of place in a nuclear submarine (seriously, it was battleship blue, larger than a football and had wiring options for three-phase), and one-pipe plumbing that just about got you above 'refrigerate' in winter. It was shit.

Here, I have a modern combi. Turn on hot tap, hot water comes out. It's a goddamn revelation I tell you.

To be fair, I expect that a shit combi would still be shit. The one here is a good 'un, it's a Valent 37 Somethings (kilowatts?) IIRC and can cheerfully drive a house the size of yours.

Fwiw, we have an electric shower,

Again, at the old house,

I had an electric shower fitted which was cold-fed. Did its own heating, had bog all to do with the boiler.

Get a combi. If it stops working, the boilerman fixes it. No questioning whether the fault is with some weird valve on a tank, some controls or wiring problem or other nonsense. As for heating a bigger house, we have seven bedrooms, three bathrooms and the Baxi handles it just fine.

I'm a landlord too and one of my houses needed a boiler a few weeks back, my usual guy was tied up for the next month on a contract doing new build installs, so I gave Boxt a go. Spoke to them and placed order at 2pm on the Tuesday. Wednesday 7.45 am the plumbers arrived, converted from tanked to combi system, removed tanks and redundant pipework and had a WB Greenstar 4000 Life running by 4pm. A second visit by an electrician on the Thursday cleared out the jumble of controls for the old unit and a ten year guarantee too.

I share a home with 3 women and all four of us can have a shower without running the tank empty

Are you all showering together?

I'm a combi fan and, fingers crossed Worcester Bosch. Mine is errrr, about 10 now I think and has been fine. I have read they aren't the go-to anymore though.
While I'd stay with gas is I had it, if I currently had a tank I'd likely keep it, as the next change will likely be to a great pump or such and I'm guessing they will work with a tank

When our 20+ year old Potterton packs in we won't be going down the combi route.
2 people I know that have combis had issues in the depth of a couple of winters with them, 2-3 weeks without hot water and obviously heating.
At least we can use the immersion if needed and it is handy having an airing cupboard.

Another Worcester Bosch Combi owner here, ours has been fine for the 7 or so years it's been installed. Had cheap crap in the past and my god were they bad, I can see why folk would be put off.

I can see the attraction of a tanked system if you are planning on alternative heating sources in future but tbh I'd just be doing it now.

On combi's, correct me if I'm wrong but are system boilers not all condensing boilers now anyway? So really it's not going to be any more or less reliable than a Combi where it counts.

We had a pin holed manifold in March both of which caused leaks down through the kitchen ceiling. This is a 9 year old Worcester Bosch Combi which we had fitted when we moved in.

Is that a manifold on the boiler? If not I'm not sure about the relevance other than the system not being maintained (assuming it's a corrosion issue).

I’m a combi fan and, fingers crossed Worcester Bosch. Mine is errrr, about 10 now I think and has been fine

Well, you've jinxed it now, obviously...

ne last thing – get the biggest hot water tank you can – they keep water hot for a long time and it’s nice to have acsess to lots of hot water

Or get a combi then you get piping hot water whenever you turn a tap on, for as long as you like!

There are five of us in our house including two teenage daughters who both have an en-suite and shower for about 30mins at a time. My son likes a (swimming pool volume) bath every day, as does my wife. We use loads of water. Never once thought a tank would offer us anything more or fix a problem, we have lots of pressure and it just works

Do you want hot water on tap? -chuckle-

Combi

Sometimes the jokes come naturally and sometimes you have to faucet.

+1 for WB combi from me after 15 years good service, but helps if you get install/service regularly from approved fitter. It will go wrong and so the long warrenty + WB engineer onsite is worth the extra cost imho.

You must size combis for hot water output. Bigger the better.

I have been advised If I had my conventional boiler replaced with a Combi that I would need a bigger pipe fitted between gas meter and boiler.

So something to get checked out.

I have been advised If I had my conventional boiler replaced with a Combi that I would need a bigger pipe fitted between gas meter and boiler.

So something to get checked out.

That's interesting- also explains why mission the neighbours who have had it done have big ugly pipes on the walls

Or get a combi then you get piping hot water whenever you turn a tap on, for as long as you like!

As I mentioned before, I had a combi in my last house and hated it. The power we get from our unvented system is manyfold better (almost power shower level of power) compared to the combi. Perhaps they are better these days but I would need lots of convincing to go back.

I have been advised If I had my conventional boiler replaced with a Combi that I would need a bigger pipe fitted between gas meter and boiler.

Generally a combi should have a 22mm gas pipe going to it. You might get away with a 15mm if there aren’t any other gas appliances in the house

That’s interesting- also explains why mission the neighbours who have had it done have big ugly pipes on the walls

They changed the regs about 15 years ago, max allowed pressure drop on full power is 1 mb, which you normally can't achieve on 15mm pipe, hence so many houses have new 22mm pipes running externally around the house then into the kitchen etc through the wall (cheaper than chasing though concrete floors etc).

only ever had combi and moved to a house that is a water tank - its a definite step back

When this boiler breaks it will be back to a combi without any thought to it.

Heating water to just sit in a tank is a waste of energy, and you have to plan more. Nothing as good as coming in from a cold bike ride to find someone else has used all the hot water

Heating water to just sit in a tank is a waste of energy,

Combi boilers do this also.... But a smaller amount....all the time.

I fitted a combi 10 years ago as the whole vented system I had was in poor shape and a combi was the cheapest way to get the whole lot updated.

10 years down the line I wish I'd stayed with a tank as I have solar going on the roof which would have been nice to have had the option to fire an immersion into a tank to make use of the electric fully and vastly reduce my reliance on oil.

Next time round it'll probably not be a combi. But likely a considerably smaller system boiler.

Grandparents have a solar PV feeding a vented tank in the airing cupboard with a boiler the size of a microwave mounted high up on the wall in the utility

My combis the size of a washing machine.

FunkyDunc

Heating water to just sit in a tank is a waste of energy, and you have to plan more. Nothing as good as coming in from a cold bike ride to find someone else has used all the hot water

I do agree about the waste of energy heating a volume of water that might or might not get used at some point.
But, we generally only have the hot water on for 1 hour per day & I can't recall ever running out of hot water (we've been in this house for 10 years).
This might be because we have an electric shower, so don't draw on the hot tank for that.
But, if we did use water from the tank for a normal shower we'd just adjust the timer to heat the water to suit our showering habit.
On our controller, we have an 'extra hour' button & so I just stick that on if I know I've used a fair bit of water.

But, having said all that I am thinking more & more that a combi would probably be the best option for us.
We have an electric shower, so if the boiler fails we still have the ability to shower. We just have no hot water for other stuff (stick the kettle on) or heating.....

Keeping a traditional system with a cylinder & an immersion for back-up seems a bit OTT for something that might happen once in a blue moon.

We have an electric shower

And they are expensive too, OK you are not going to go out and change your shower too right now, but bills would go down if you did.

Heating water to just sit in a tank is a waste of energy,

Modern hot water tanks keep water very hot for several days. I agree it would be wasteful to have a large tank for a small flat with a single resident, but if you have a larger property and a tank suitable for the size of the household then any 'waste' would be negligible.

We’ve got a traditional system with a boiler / hot water tank / cold water tank and it’s gravity fed. So water pressure on its own both hot and cold isn’t great. However we have one pumped shower which therefore has good pressure, plus 2 electric showers. The downstairs electric shower is better then the rebel LT oarhetic electric one upstairs as it’s plumbed to mains pressure rather than the cold feed from the tank in the loft.

When we had to replace the boiler a few years ago when we had an extension we had a much bigger gas pipe out in to meet regs for a 30kw boiler (right faff that was)- but we put a boiler in that could be converted to a ‘system boiler’. I think that’s what people are referring to as unvented above.

We’d lose the cold water tank (which would free up loft space), have to fit a newer / higher pressure hot water tank and everything would broadly be on mains pressure as I understand it. I’d quite like to do that at some point as it sounds ideal.

When I lived at my parents they had a combo boiler and I wasn’t a fan. If you were in the shower and someone used a hot tap somewhere else it would go cold / lose pressure etc. So for hat reason unless it’s a small house with only a few people living there I’d avoid a combi personally.

Heating water to just sit in a tank is a waste of energy, and you have to plan more

Fair enough we have an electric shower but we've never run out of hot water - one or two hours in the morning, one or two hours in the evening and we are sorted, even when the kids were small and having baths

Get a combi. If it stops working, the boilerman fixes it.

When? Mate of mine recently had to wait 3 days to get a plumber to come round because around here they're just blocked out...and its summer! OK it wasn't a combi so he was OK, but if it were a combi he'd have been screwed for 5 days.And then there is the potential for a shortage of spare parts. A previous boiler of mine broke down many years ago and the part it needed was discontinued as it was an older model. Took a few days to source a part before it could be fixed...again lucky I didn't have a combi and still had hot water.

Heating water to just sit in a tank is a waste of energy,

No its not. You're only heating up the water you use once you've initially heated the tank. its not heating the full volume of the tank every day...rarely do we run it empty of hot water, so you're just topping it up. The tanks are super insulated. Before I replaced my tank and had the old style copper tank, foam coated with a jacket my airing cupboard was nice and toasty. Water engiergy. My current tank is so well insulated the airing cupboard is no longer warm and toasty. All the hot water pipes are lagged and you get a bit of heat from them when hot water is running through them when you're drawing hot water, but normally the airing cupboard is alot cooler than it used to be. They're extremely efficient systems.

I think the issue here is that people who don't like combi boilers are likely basing their experience on older, under powered boilers. Modern combis are reliable, chuck out lots of hot water very quickly and easily cope with a more than one hot water draw at a time.*

*all assuming that you get the right boiler for your house and demand.

I think the issue here is that people who don’t like combi boilers are likely basing their experience on older, under powered boilers. Modern combis are reliable, chuck out lots of hot water very quickly and easily cope with a more than one hot water draw at a time.

There may be an element of that, but a quick Google pulls up site after site that lists the pros and cons of combi v system boilers and they all seem to suggest that larger households are generally better off with a system boiler if no significant drop in water pressure when multiple devices being used is a requirement.

There's a load more work money for a plumber installing anything other than a combi, so expect marketing websites to sell where the profit is.

There’s a load more work money for a plumber installing anything other than a combi,

But if you already have the HW tank etc, then swapping an non Combi for a non Combi will be almost as easy as swapping a Combi for a Combi (you might have to run up the stairs to the airing cupboard a couple of times).

There’s a load more work money for a plumber installing anything other than a combi, so expect marketing websites to sell where the profit is.

Strange that many modern new builds are ditching the combi. That would not happen if combis were cheaper(and as easy to get the house to the energy level it needs to get to to pass design inspection)

There’s a load more work money for a plumber installing anything other than a combi, so expect marketing websites to sell where the profit is.

But they aren’t doing that - they are saying that smaller properties with fewer people / situations where consistently high water pressure isn’t a requirement then a combi is a good option. They aren’t saying they aren’t good, they are saying that for SOME users a system boiler is a better option, for others a combi.

We're in a 4 bedroom house, built in 1997, still on the original system boiler. I too, don't get the "hard work"  comment, the water heating comes on, on a timer(!) twice a day, an hour each time. We've never run out of hot water, but there's only 2 of us (sometimes a house full, though).

The dear wife has been hankering after a new boiler, so it looks like I'll be coughing up. It'll be a system boiler for us again.

Heating water to just sit in a tank is a waste of energy,

heating water extremely quickly is a waste of energy too. Overall it nets out, which is why there isn't any environmental pressure to/from one of the solutions.

Its worth noting that the flow rate on a combi boiler is pretty poor. If someone in your house likes baths, a good tanked system will typically fill it much quicker.

Well I’ve certainly not experienced any of the problems people are talking about with combi boilers. As long as you spec the big enough boiler for your house and have enough flow, a shower will not go cold if someone else turns a tap on.

In our current house our system boiler looses about 10 deg of heat every 6 hrs or so.

As a family our hot water requirement varies day to day, sometimes we heating water just for the sake of it, others say waiting for water to heat up

Couple things about combi boilers.

Firstly there are only two types of combi boilers; ones that are broken and ones that aren’t broken... yet. One combi I had the manufacturer had an eight year lifespan (this was back in the 90’s, pilot light, etc.). And they never breakdown in the summer. One of mine went dec 29th and it was -10 outside. Another (a Worcester) took three weeks to fix (to be fair, that was the plumbers, not the manufacturer) in January. So I’m a little biased. Combi’s have more internal moving parts (hot water priority) so something else to fail.

Secondly: yes standing losses are less and you only heat the water you use. Distribution losses however you also need to factor in. Unless your in a Passivhaus chances the house designer hasn’t even given the boiler location (verses where your hot water outlets are) any thought. Boilers tend to be located for convenience of getting a flue out, not where water is required. A hot water cylinder is easier to locate centrally. If it’s in the wrong place you’ve a big slug of (cold) water to get through the pipes before hot starts to come through (true in a cylinder set up to though). HW cylinders can come with immersion back up (I always spec them with, and that’s on non-domestic).

Thirdly: in a combi all water is heated instantaneously. This means that you are ruled by the laws of thermodynamics. An electric shower (which most people moan about being ‘underpowered’ is approx 10kW (direct electric, no trans losses). Mass flow = heat/(Cp. delta T). What’s your shower flow rate? 6 l/min minimum. If you like a lot of flow, double that (worse if you’ve multiple heads/jets). How much output does your boiler have? 28kW min, maybe as much as 40. A system boiler is what, 10-15? And an hour or two to hit HW storage temp... so, yes you will need to upsize your gas pipe (from the meter). From memory, 50kW gives 0.3l/s at 50 deg C, a bath tap is 0.2 l/s iirc. Which is why combis are better suited to flats than houses. How many bedrooms/en-suites? How many simultaneous showers/other water outlets in use? How big is your boiler again? This is why house combis are bigger as they are semi storage (usually a small internal HW tank).

Forthly: decarbonisation of heating. It’s coming. Gas is dirty, from 2025 it’ll be illegal to put Nat gas fired boilers into new build homes (Scotland anyways) and net zero is 2045. Decarb presently means electrification and you’ll be back to HW storage tanks...

We have a conventional boiler and tank, have no idea whether it's vented or not. It's been in the house for nearly 30 years long before we bought the place.
Having a tank of hot water was good for us before the kids became teenagers. Between the two of them they can empty the tank when taking showers.
We have investigated updating the whole system, to see what our options are. Most quotes have come in to replace the whole system with a combi setup. Since I'm working from home I don't really want that kind of disruption.
We are constantly bombarded with offers on this government boiler replacement scheme, I don't know anyone who's done that. Anyone on here have any experience?

Well, I am quite heartened (is that a word) by this thread.

I thought it was just me being my usual indecisive self, but it appears that the choice is actually quite a difficult one & comes down to a lot of different factors.

asbrooks

We are constantly bombarded with offers on this government boiler replacement scheme, I don’t know anyone who’s done that. Anyone on here have any experience?

I've not even heard about that. Any info or links?

Having a tank of hot water was good for us before the kids became teenagers. Between the two of them they can empty the tank when taking showers.

So is it the case that a modern system boiler could not be set to automatically reheat the hot water tank if it drops below a certain temperature instead of just heating for an hour a day or something?

Or is it that they do reheat automatically, but not fast enough?

Or is it that they do reheat automatically, but not fast enough?

Ours reheats fast enough to allow for the four of us to have showers at the same time one after the other (ie, two showers used concurrently twice). It sometimes doesn't quite manage to keep up when one of our daughters has a shower bath (she fills the bath whilst showering then sits in the bath when it is full to the brim). But it is a massive bath (enough for me to lay out flat in it) and it also has very steep sides so the volume of water required to fill it is huge.

The advantage of having a HW cylinder is if you have (or add solar PV) you can heat your HW directly from that, effectively for free. More and more new builds seem to come with solar PV built into the roof.

The issue is whether a decent make of combi can ever compete with (or get close to) an unvented system in terms of shower pressure etc.

Easily and indeed much better - you just need a boiler with the capacity. Ours is the best shower I have ever used - run off a combi

So is it the case that a modern system boiler could not be set to automatically reheat the hot water tank if it drops below a certain temperature instead of just heating for an hour a day or something?

Yep, just stick a thermostat on the tank and leave the HW timed to be switched on all day (or 24/7) but the boiler will only heat the tank when the thermostat swithes on. Pretty sure that's the standard set up for any modern system with a HW tank (as in having a thermostat on the tank).

We drop the HW tank thermostat temp down in summer as the incoming cold isn't that cold so we don't need the hot water to be so hot for showers etc. In winter I stick it up an extra 5-10 deg so the HW tank lasts longer.

Thanks @johndoh @footflaps

@stumpy01 It's called the ECO3 scheme.

I believe, or though I'm struggling to actually find anyone who's taken advantage of the scheme. I'm naturally skeptical when it comes to free stuff, but you can get a replacement boiler if it's more than 5 years old. All the mail I get through the door states that you don't have to be on benefits to benefit from the scheme. Apparently the government are throwing money at it to due to its climate commitments.

I can only find something from my local council. As with anything that nearly free with the government they don't really advertise or everyone would jump on it.

My Local Council

but you can get a replacement boiler if it’s more than 5 years old.

Our must be getting on for 30 years old, model came out in 1988.

Easily and indeed much better – you just need a boiler with the capacity.

With an unvented cylinder the hot water is at incoming mains pressure - AFAIA it's not possible for a combi to be better than the mains pressure.

With an unvented cylinder the hot water is at incoming mains pressure – AFAIA it’s not possible for a combi to be better than the mains pressure.

My thoughts exactly - and I struggle to believe that the most powerful domestic combi boilers can heat water at mains pressure and deliver it to multiple heads simultaneously at that pressure.

With an unvented cylinder the hot water is at incoming mains pressure – AFAIA it’s not possible for a combi to be better than the mains pressure.

We got a Worchester 8000 Life 40 combi installed on the cheap last year through one of the council/power company schemes.

It's flow rate is apparently 16L/min. The flow out of our bath taps is ~15L/min and it comes out hot. Perhaps we don't have the best mains pressure but is fine for me.

I noticed after a bathroom refit that shower head is limited to 9l/m and detaching that and running cold water full on gave me 15l/m (bucket test).

As there are two of us, it wasn't hard to calc that a 40kw combi would be fine. Filling bath at the same time ia going to slower than a cylinder, but we know we always have hot water (unless combi is broken)

Bigger house, more people,more showers etc and the calcs would be different.

My combis the size of a washing machine.

It's also oil fired so not a fair comparison.

Strange that many modern new builds are ditching the combi. That would not happen if combis were cheaper(and as easy to get the house to the energy level it needs to get to to pass design inspection)

Not really, as you say it's all about making the EPC score. Your standard fitted PV panels are also all but useless to your average 9-5 family so the power may as well go somewhere useful.

The biggest thing about combi's is the environmental issue, they're not compatible with storage systems so if you're looking to the future the best bet is a tanked system. But don't be under any illusion that the boiler is somehow different, it's not, it works exactly the same and has the same chance of breaking down, it's only the controls that are different.