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Where better to ask for advice on central heating than a bike forum. I have a gravity fed CH and HW system fed by an Potterton Profile boiler that must be over 30 years old - a bit like me. It's still running OK but I expect that in the next year or two it'll get to the point where it becomes beyond economic repair.
At that time am I best simply replacing it with a more efficient modern boiler (and perhaps replacing the HW tank which I suspect is getting a bit scaled up by now) or should I go for an unvented system while I am at it? What are the pros and cons for the two systems?
I am not a heating engineer.
Just to check first, mains gas, good water pressure and a regularish sized home of close to conventional construction? If so..
My advice: Pt 1, there are so few parts in the Potterton, and they are still stocked that an old school engineer should be able to keep it going as long as you choose. Efficiency gains are possible with something newer though.
Pt 2, if you aren't doing some other eco mods such as wet solar, photovoltaic solar or some wood burner with a back boiler that can be used to add heat to your tank over and above your boiler's input, then when you do come to change, rip the lot out and put a combi in. Boxt can have you a new one in at 48hr turnaround or less.
Unvented is smaller, so can fit in more places, and is less likely to get issues like dead rats clogging up the tank etc. but when the pressure tank fails (and they do more often than you might think) not only do you face a few £100 bill, but you also get to test the installation quality as a very light pressure tank full of air isn't nearly as light when it fails and fills with water.
Personally unless I had good reason to change, I would stick with vented. The boiler is a bit trickier. You'd probably squeeze 15% more efficiency maybe more from a new boiler, which is quite a lot, but if your gas bill is only say £1000, thats still a long time to pay back, and new boilers, like all things are more expensive to repair and more prone to going wrong (as I understand it, have works ongoing with a friend who is a plumber so we were chatting on this subject just this morning).
Just to check first
Mains gas, ok water pressure, 4 bedroom semi.
On our £1400 annual gas bill 15% efficiency could save us £200 pa which of course is a long payback on a new boiler. And a couple of plumbers have told me these old boilers are less efficient but worth repairing as long as parts are available because they are generally more reliable. So I’m not keen to change but recognise at some stage I’ll have to.
Do modern combo boilers work ok with pumped showers and with filling baths vs HW tanks?
A combi won't generally be compatible with any additional pump between it and the shower. If shower pressure is a priority for you, I would think about the unvented system.
It’s not just the boiler efficiency to consider, it’s the controllers as well. Putting in weather compensation at the same time will likely save even more money.
Our switch from a floor standing 35 year old boiler to a modern condenser with weather comp [b]halved[/b] our gas consumption.
I’ve also found plumbers are the worst people to talk energy efficiency with. They like what they know and they know what they like for the most part. Mine is brilliant but I had to very clearly specify for him what I wanted based on heat loss calcs and he wanted to install something a lot bigger. He was surprised when it heated the house and the water just find for a lot less gas. Great plumber though.
Yes, modern combis fill baths plenty quick. As for showers, if your water pressure is decent, you get a good shower without needing a pump. That said if you already have a pump, you’ll need to bypass/remove it, they don’t play nice together. Usually the valves installed for a power shower will be happy fed from a combi.
As bensales says, a boiler that can ration the use to the needs through modulation for outside temperature and lower demand due to adding zones or individual room controls can save you a packet, if that is your situation. If you have an ancient relative or newborns around and need the whole house 25 degrees all the time, you need shares in British Gas.
We also made big gas savings going from a 40 year old Baxi to a modern combi. Better controls obviously as well. Use around 40% less gas.
I set it up years ago to have separate zones for upstairs and downstairs. But modulation based on outside temperature sounds an interesting new feature.
Boxt can have you a new one in at 48hr turnaround or less.
They don't offer the all bells and whistles boilers necessary for weather compensation. They are a practical demonstration of @bensales maxim of they know what they know.
then when you do come to change, rip the lot out and put a combi in
10 years ago I'd have agreed with you. When I ripped out a tank and s plan system for a combi.
In today's world. - terrible advice.
Currently reinstating my tank.
They don’t offer the all bells and whistles boilers necessary for weather compensation
I just checked and the first boiler on the list they offered me has weather compensation...
Isn’t anyone opting for a combi now, lining themselves up for a higher bill later on when heat pumps are almost mandatory?
Isn’t anyone opting for a combi now, lining themselves up for a higher bill later on when heat pumps are almost mandatory?
Given the average age on here it'll be the next owner they are setting up but yes that's the changing world I was on about.
Big bucks but solar , battery pack and ashp could be an option?
Or solar, battery and bulk water tank, utilizing octopus flex to heat the heat storage tank. Sell electric back to the grid when your battery is full, then use battery to trickle heat the bulk tank of an evening. Gives option of car charging too.
Probably wrong side of £10k after the ashp grants so a long payback period,
"" Imo/ ime you need to massivly overspec a combi to get a decent shower unless you have a decent sized house so need the power for heating. Look at the flow rates that can be achieved with a decent hot water""
Yes and no . Modern combi boilers have the ability to turn the flame right down once the heating system is up to temperature. So a 6:1 boiler will run at roughly 5kw output, giving 1kw per room, but can deliver around 10 LPM of hot water for showers / baths. Dependent on incoming water temp and desired hot water temp
Probably wrong side of £10k after the ashp grants so a long payback period,
That's obscenely optimistic
I didn't say how far over £10k though. And even with the grants it will be near £20k after all the bits and bobs have been added plus labour.
Our switch from a floor standing 35 year old boiler to a modern condenser with weather comp halved our gas consumption.
I think this is the reason for having plumbers say don't change the boiler. OK so the boiler can have smarts, but generally there's usually way better ways to save on the heating bill before you chop in a boiler that works well. Check out the warranty too, some of these quick install / funded ones have a 2y warranty on them! When my 15yo boiler broke* Worcester came round and practically rebuilt it with new parts.
Example of energy saving for me only this week. At the moment Im doing some work in the utility on my thermal store set up. I removed a ceiling (single story extension with traditional rafter/joist roof) and found that while the pipes were laid below the (terrible) insulation, the pipes at one end where they enter the older house rise up above the insulation (its a wonder they never froze) then dived through a large hole in the wall. This large hole goes into the ceiling/floor void of the main house, and was open to the cold part of the roof space in the utility. So for the longest time Ive been exchanging warm air from downstairs in the main house into the roof space! God knows how much thats cost me over the years in lost energy.
* It had a burner viewing window that broke and set fire to the wiring loom. OK so thats bad but still, it was 15 years old.
If you need to replace it then maybe take advantage of the £7,500 heat pump grant? It might not be as bad as others say here. You could try running it during the day with the flow temperature down at around 40 degrees. This might be the last chance this year to test this before it warms up properly.
*gazes angrily at sleet*
@TheFlyingOx that's a pleasant change as they weren't when I bought new around 3 years ago. I haven't been back as once there's a new boiler installed you're not in the market anymore!
I think this is the reason for having plumbers say don’t change the boiler. OK so the boiler can have smarts, but generally there’s usually way better ways to save on the heating bill before you chop in a boiler that works well. Check out the warranty too, some of these quick install / funded ones have a 2y warranty on them! When my 15yo boiler broke* Worcester came round and practically rebuilt it with new parts.
Well, it does depend on the boiler. If you’ve got a very old, non-condensing one, that can’t modulate, then change it. Otherwise modern controls won’t make any difference. Even fairly recent boilers can’t modulate down as far as current ones. And that’s the trick, finding something that can modulate down to almost off when controller via weather compensation but doesn’t actually turn off and start cycling.
Bensales +1.
Engineer quality is important too. There are loads of plumbers out there that know how to stuff a box on the wall and connect pipes and know bugger all about energy flow and efficiency.
I went through 7 before I found one that was knowledgeable enough to have a proper conversation about it. Most just wanted to spec an over powered boiler and rely on 'modulation'. So they didn't have to think about it.