I have the opportunity to put a new boiler in because we're doing an extension which will give us the opportunity to remodel the utility room containing the current (original) boiler - a 35 year old Ideal Mexico RS80 old school heating boiler. It has a hot water cylinder, expansion tank, cold water tank feed in the loft. The house is 4 bed detached (35 years old) and usage is
- 10 radiators, a large wet UFH system in the kitchen / diner
- 2 bathrooms each with a shower via a shared pump
- 3 teenagers and a spotless wife, so showers get hammered and need to run simultaneously, likely whilst heating is also running
We manage fine with the current cylinder (shortens shower time) and everyone's learnt to use the boost and immersion for the crazy times they choose to shower, so big question is swap for heating or system boiler, or move to combi. We're not ready for ASHP right now. Questions:
- Should I switch? I'd be keen to use less gas but the current boiler just works and has been great for the 18 years we've been here.
- Will a combi be sufficient? I don't believe we have water pressure issues (hilly West Yorkshire), but not clear why we have a shower pump. Are combis high capacity enough or is it easy to hit their limits with our demands?
- If I don't go combi, is heating (straight swap) or system better? I'll keep the loft stuff but having pipes and tanks in the loft is mildly unsettling
- Which manufacturer, and is a stainless setup a key factor? A bloke I know says Viesmann
- I'm due a flush of the system so any money on that could be put to a package for flushing and fitting and it's just feeling like the right time to make a change
Any boiler, even a small combi will meet your heating needs. If choosing a combi, bigger gives higher HW flow. Personally I prefer combi as simple and no extra faff with tank etc.
we’re also in hilly WY with good water pressure. We did total reno 4 years ago and went with ideal vogue 42 for high flow 17 litres and 10 year warranty. Like you our house previously had a shower pump which went when new boiler was put in.
pros, simple efficient and masses of HW on demand. Showers are amazing. If we run 2 showers simultaneously the pressure drops to what I’d say is average domestic shower.
Only con is HW takes a minute to reach furthest taps which is wasteful. Sink next to boiler is instant HW.
personally I see system boilers as more wasteful and potentially limiting in HW as you have a big busy family demand.
In true STW someone will be aling soon to give opposing view. But that’s ok, you can make an informed choice.
We are in a similar property on room and shower count. We have a combi and it is massive to feed the hot water demand. Yet we still can only use one shower at once. We've looked at a heat pump but for mainly aesthetic reasons (only location is garden) we are going for a new boiler. As we have really good water pressure we are going for a system boiler with an unvented tank. This should allow multiple showers simultaneously or shower + tap. It also means we can size the boiler more appropriately, i.e. don't need an oversized boiler (as far as heat requirements are concerned) to heat water. The new tank will have a HP ready coil which I'm told means a system boiler can also reheat it really quickly. Aim of this system is no/very little pressure drop with multiple showers. For comparison I think our current boiler runs 18 or 19l a minute for water and cannot support 2 showers or shower + tap without temperature and flow fluctuations. It's rated at 35kW for heat, our worst heat loss calculation was 15kW! The replacement system boiler (20kW) can also modulate all the way down to 2 or 3 kW which should produce a more efficient system.
You probably have a pump due to having a vented water tank. I.e. the tank is not at mains pressure. If your water pressure is good then with an unvented tank you should not need the pump.
There's a reason combi/condenser boilers are the most popular.
What size/power you get is a different conversation, but having a constantly warmed up hot water tank is VERY innefficient, verses a modern combi boiler.
They are cheaper and easier to install?
I don't think they are Mattyfez as keeping the water hot is not the only consideration. If for example an oversized combi has to cycle it won't be condensing anyway so that efficiency has gone up the flue. I've spent way too long recently looking at spec charts. The cheaper combis don't modulate as low which combined with over sizing to meet hot water demands is a bad combi ;P. Not an expert though so better to listen to bear who I think does this for a living.
System boilers can also condense btw.
Don't think about what you want, fit what the house should have for when you come to sell it.... Which you will do one day.
I'm my mind a 4 bed detached House should not have a combi.
TBH you may not get your money back in fuel savings.
I would be looking at changing the tank to a larger (250L) invented tank.
That will give you more hot water, equal pressure throughout the house and mark you can get rid of the pump and the header tank in the loft.
You could also get one that works with solar and Heat pump for future proofing.
having a constantly warmed up hot water tank is VERY innefficient, verses a modern combi boiler.
Not the case at all if you have PV.
That sounds like a money pit.. Have you run the numbers on that?
Heat loss of a modern cylinder is pretty low.
I’ve not run the figures but water heating is a small percentage of the load compared to heating.
with a combi somebody goes to the toilet, goes to wash hands, waits for hot water, boiler fires for a minute or so shuts down. Very inefficient. And combos are not the answer to big loads of hot water they just can’t cope with flow rate.
Nixie - I can get you a heat pump you fit indoors…..
or a much better looking one…..
ASHP.
if you really are set against that then a system boiler. A new boiler will be more efficient than your [edit] 35 [/edit] year old one.
Combis are ok if you have limited space, few people, a small house, and not much need for hot water. A system boiler with a big, unvented, tank will provide plenty of hot water efficiently and will heat well.
A modern unvented cylinder will keep its contents hot for some time. It does not need to be constantly heated, that would be unnecessary. Because of the timed production of hot water the boiler output for a system boiler can be fairly constant when heating the house and/or water. No need to drop the heating provision and crank up the output for the hot water demand like a combi .
Get a Vaillant or Viessemann or similar. Don’t get a Worcester-Bosch.
But in your position I would avoid boilers altogether and get an ASHP. I’d not expect any cost savings, but the reduction in CO2 emissions would be great. The elimination of highly flammable gas and its associated standing charges from the house would be nice extras.
but having a constantly warmed up hot water tank is VERY innefficient, verses a modern combi boiler.
I've just went from a combi to a system.
I'm not finding this at all. If anything my bills have come down.
Been able to turn my boiler right down as a result. It's also much smaller as it doesn't need instantaneous flow. Combi was 28kw
15 years ago I fitted the combi . It was good for my needs a t the time but now I have the space a system is the better option.
Hooked up to PV and solar thermal -cant do that effectively with a combi. Worst of all worlds
A new boiler will be more efficient than your [edit] 35 [/edit] year old one
It will but even if it's 20% more efficient (doubtful but I'm not a heating guy) that's what, £200 a year saved?
That would take a long time to repay the cost of a new new boiler plus fitting.
Heat loss of a modern cylinder is pretty low.
1.87kw/24hr
So it's not negligible. But it is low especially since your tanks rarely going to be static for 24lhr
We went combi a few years ago.
Pros: Freed up cupboard space from cylinder, pump, zone valves, etc. Freed up loft space, no tanks.
Cons: No "airing" cupboard. DIY repairs more difficult, everything is in the boiler case. Heat exchangers more efficient and so more sensitive to blockage (this may be true of all modern boilers??). If the boiler breaks, everything breaks. Shower cartridges needed changing, new shower if you can't get the parts. You wait an age for hot water as mentioned^^ and it's inefficient during that time.
£££ dunno, never made a comparison
Balance: not convinced either way
I personally would be moving away from gas, looking at ASHP, solar and batteries.
I know it's a leap, but....
We've a 7 year old boiler and are saving and planning for the day it dies.
Trail rat - that’s not a huge amount when you look at how many kw you lose through heating…..
You could off set that loss by spending some money draughtproofing and cutting the heating load.
also if that heat is lost indoors then it contributes to the heating so it might be lost from the hot water but it partly warms the house…..if you are being really pedantic and look at things in passivhaus ways!
Unless you are noticing massive bills due to your current system I wouldn't change it. Yes a new system will be cheaper to run but you'll never save anything like the replacement cost. It's possible a new system might even encourage longer showers and put your bills up. I'm generally a fan keeping what you have and avoiding constant upgrades.
@scuttler - We have that same boiler, if you do replace it can you send me pictures of the vent as it might be the same version as ours and I'm looking for spares to keep ours going.
Some top insights here - thanks y’all. OP.
that's what, £200 a year saved?
I’d put the CO2 emission saving above nonsense like reduced running costs.
Trail rat - that’s not a huge amount when you look at how many kw you lose through heating…..
You could off set that loss by spending some money draughtproofing and cutting the heating load.also if that heat is lost indoors then it contributes to the heating so it might be lost from the hot water but it partly warms the house…..if you are being really pedantic and look at things in passivhaus ways!
I wasn't insinuating it was i was quantifying the typical losses
well looks this place has had the reddit upgrade.... not how i expected that response to enter the chat....
that's what, £200 a year saved?
I’d put the CO2 emission saving above nonsense like reduced running costs.
Is that lifecycle calculated from conception to disposal or just considering gas used.
There's a reason combi/condenser boilers are the most popular.
there sure is - they are space efficient. They are a compromise in every other way.
Whilst running costs are part of the decision, so are CO2 emissions, as are the tangible and intangible costs for the unscheduled failure of a 35 year old boiler. Definitely not doing this for the LOLZ.
[not relevant to OP, but]
Just to complete the picture, a combi can act as a system boiler too. I did a top-floor flat refurb where the combi had been recently replaced but wasn't going to have the oomph for a decent shower so had a full break tank, pressure pump and megaflo put in the roof space for the shower but the combi still served the kitchen. With a bit of zone valve trickery, the heating side of the combi was used to heat the megaflo. Shower is completely unaffected by kitchen taps going on as a bonus.
[/]
Not a combi if only for the fact that when it goes wrong your spotless wife won’t be spotless.
won't it be old boilers that might go wrong?, mine is an Ideal Vogue (12 yr warranty) and has only needed a call out once in 10 years, that was for an issue that didn't stop us using the boiler and the Ideal guy was out to us the same day.
We swapped our system boiler with tank to a combi boiler 3 years ago.
One of the main reasons for doing this, was so we could move the boiler out of the kitchen & into the airing cupboard as part of work to remove a brick-built cupboard with chimney above it that housed the system boiler. We couldn't have the chimney down until the boiler was moved.
We ummmmed and aaaaaaahed for ages about whether to stick with a system boiler or combi, but virtually everyone I spoke to seemed to recommend a combi. I had my doubts, but that's what we went with.
Our old boiler was a clattering old mess of a thing and parts were becoming hard to get for it. No idea how old it was, but I would guess at least 20 if not 25 years old.
The new boiler is not noticeably cheaper to run than the old one. I mean, it must be better (it doesn't have a permanently lit pilot light for a start), but the difference has not been enough to really notice on my energy bills. The change did coincide with the energy crisis and spike in costs caused by the Ukraine war, so perhaps if I dug into the annual kwh amounts, it would be more obvious.
So - cost benefit - not noticeable.
It takes longer for hot water to come through the taps. Just long enough to be annoying & quite wasteful.
With the old system, we had a immersion if required, for when the boiler went wrong. We now don't have that redundancy which does play on my mind; however rarely we actually needed to call on it.
In hindsight, I feel it would have been better for us to have gone with my gut instinct and stuck with a system boiler.
For reference, it's a 30Kw Ideal boiler we've gone with. It's what the fitter recommended.
Not a combi if only for the fact that when it goes wrong your spotless wife won’t be spotless.
won't it be old boilers that might go wrong?, mine is an Ideal Vogue (12 yr warranty) and has only needed a call out once in 10 years, that was for an issue that didn't stop us using the boiler and the Ideal guy was out to us the same day.
old boilers tend to be simple and robust, minimal electronics and heavy componants not lightened in the name of efficiency
Not a combi if only for the fact that when it goes wrong your spotless wife won’t be spotless.
won't it be old boilers that might go wrong?, mine is an Ideal Vogue (12 yr warranty) and has only needed a call out once in 10 years, that was for an issue that didn't stop us using the boiler and the Ideal guy was out to us the same day.
old boilers tend to be simple and robust, minimal electronics and heavy componants not lightened in the name of efficiency
Presumably an unvented tank runs from mains pressure and so doesn’t need any tanks in the loft?
And so if I want to replace a combi with one the only extra space needed is for the tank?
FWIW my Combi does my head in but I think it’s an issue with ours rather than a general combi issue. Ours doesn’t kick in unless the tap is nearly fully open, so if you turn the tap down a bit it shuts off and you get a cold blast which then takes ages to get hot again once you turn the tap back up.
(it also takes ages for water to get to the bathroom but there’s not much I can do about that without putting the boiler in a bedroom).
OP here, getting strong vibes for a system boiler, dump the shower pump and stuff in the loft but keep the assurance of a tank (which works for our circumstances) and immersion back up. Presumably as well as the boiler itself I’ll need or benefit from a new cylinder to go unvented??
35 y/o boiler is surely going to run into spares availability at some point. Running costs won’t change that much - especially as most boilers in UK are set up with high flow temperatures so they’re rarely in condensing mode anyway. Whatever you fit get a good fitter who will fit weather compensation controls
Personally, I would not fit a gas boiler now. If you’re doing remodelling/rework it’s the perfect time to move to ASHP.
but if you’re set on keeping gas then a tank that can be fed by an ASHP will mean less rework when one is fitted in future (and e radiators can work at low flows temps will make gas more efficient).
your other option, which I have now, is a storage combi - We’ve a Viessmann that’s been faultless for 10 years. No issue running multiple taps at once at mains pressure. No wait time as hot water comes from the (small) tank. Modulates very low for heating.
https://www.viessmann.co.uk/en/products/gas/vitodens-222-f.html#vorteile
- 35 y/o boiler is surely going to run into spares availability at some point.
Ours is around that age (Potterton Netaheat Electronic), fan died this week and found no shortage of spares online. Had one delivered next day and back up and running an hour after that. I intend to keep it going until the heat exchanger finally rusts through...
Our glow worm ultimate is 26 years old now and the only issue it has is the fan bearing sticks sometimes but I can free it up with about ten minutes work. Replacement fans and PCBs seem plentiful still.
Presumably an unvented tank runs from mains pressure and so doesn’t need any tanks in the loft?
And so if I want to replace a combi with one the only extra space needed is for the tank?
FWIW my Combi does my head in but I think it’s an issue with ours rather than a general combi issue. Ours doesn’t kick in unless the tap is nearly fully open, so if you turn the tap down a bit it shuts off and you get a cold blast which then takes ages to get hot again once you turn the tap back up.
(it also takes ages for water to get to the bathroom but there’s not much I can do about that without putting the boiler in a bedroom).
Soooo… we now need a new boiler, it’s pissing water out of the bottom from the main burner / heat exchanger.
Had a quote this morning for basically like for like replacement with another combi. I asked about fitting a storage Combi which he didn’t really seem keen to quote for…
Is it just not a common thing or does the company not want to fit one because it’s more hassle.
I realise they’re probably mainly for bigger homes but surely it fixes the main annoyance of waiting for the hot water to kick in?
First house with an unvented cylinder here (Megaflo) and only heat water once daily. It seems to stay hot forever ie after 21 hours the water is still hot enough for washing up.
I'd be going pressurised system boiler. You can probably get rid of the shower pumps.
this
having a constantly warmed up hot water tank is VERY innefficient, verses a modern combi boiler.
is nonsense. A modern, insulated tank costs about 5p/day to keep warm (0.7kwh lost per day on this model -> https://modbs.co.uk/news/fullstory.php/aid/18567/Viessmann_92s_A__rated_hot_water_cylinders_.html ), and that lost warmth is just going back into the house, where for half the year you use it.
I wouldn't bother with the boost button either. Just run the hot water on 24x7 and you always have hot water. If the boiler is big enough you'll never run out. Due to the efficiency of a modern tank, the difference between heating 24x7 and once a day is approx 1p/day
If you have the space, a modern unvented cylinder is a great thing, near limitless supply of hot water, if the boiler breaks it doesn't matter , can supply multiple showers at once.Very fast Re heat time.
The only reason to go combi is if you don't have the space for the cylinderand/or on a tight budget.
You definitely don't need to set times when the hot water is heated, just leave it set for 24/7 and the cylinder thermostat will just call for heat when the temperature of the water in the tank drops below the set point.
We swapped from a 38 year old heat only boiler and very old small 100litre vented cylinder, to a new heat only boiler and 250 litre unvented cylinder, and it's been great. We Never run out of hot water anymore, aNd it costs nothingto heat the hot water, about 10kwh of gas per day to heat enough water for our usage.
I’m currently heating 340 litres of water for less than £1 with a heat pump every day.
Storage combi’s are a pain to work on and in my experience not very well made and also expensive!
And combos are not the answer to big loads of hot water they just can’t cope with flow rate.
they can. mine will run two really good showers at once
mine will run two really good showers at once
Then it's vastly oversized for your heat requirements.
Two showers isn’t necessarily high flow though. Also what combi have you got to run that? Often the high flow, Worcester 440 etc are more expensive than a boiler & cylinder set up. Some of the storage combis are actually a cylinder and combi combined and again are often more expensive.
With a combi you will always be limited to the maximum flow rate it can deliver, unvented you can deliver a lot more if you need.
I realise they’re probably mainly for bigger homes but surely it fixes the main annoyance of waiting for the hot water to kick in?
I think it's also important to mention that the wait for ho****er you experience. Isn't you waiting for the combi to kick in. You'll have to wait regardless of combi or tank unless you have a circulation system fitted.
Our Viessmann has been trouble free for 10 years but yes, it wasn't cheap. However, it does give effectively unlimited hot water at mains pressure while only storing 100L of hot water rather than the 350 you might typically have on a tank (that spends most of its time just gradually losing it's heat to your house).
However, large tank and heat pump would be where I'd be going if I was fitting now.
I realise they’re probably mainly for bigger homes but surely it fixes the main annoyance of waiting for the hot water to kick in?
I think it's also important to mention that the wait for ho****er you experience. Isn't you waiting for the combi to kick in. You'll have to wait regardless of combi or tank unless you have a circulation system fitted.
This is true, I'm hoping to get the pipework shortened to the bathroom at the same time which I hope should help the initial heat to the tap time. It currently runs a slightly convoluted route via the 22mm pipework.
Do modern combis keep running at low flow rates? Because compounding my issue is that if I turn the tap turn to say half way it will go cold and then I have another 90 seconds waiting for the hot water to come back again.
Vitodens storage owners...
What happens when the 46l tank is emptied? Presumably it just acts as a "normal" Combi and supplies hot water at a lower flow. It doesn't go cold until it can heat itself back up again... does it?
I don't think it does but it's difficult to find details!
And will it still provide hot water from the tank with the tap barely turned on, for when you just want a trickle of hot? So below the flow that the boiler would fire up for I can still get hot water out the tap?
