Replacing 2 boilers with 1 larger one. Pros and cons please.

silvercar

We currently have two boilers serving different parts of the house:

1. Boiler A is 22 years old. non- condensing conventional boiler. In the original part of the house, serves 14 rads and the tank serves the hardly used main bathroom that has an electrically pumped shower.

2. Boiler B is 12 years old. non- condensing combi boiler. Serves 2 en-suites and 4 rads.

Both are nearing the end of their lives, possibly boiler A will need replacing soonest.

Option 1

Replace Boiler A now with another conventional boiler. Gas pipe to it is only 15mm and current regs mean that will need updating to 22mm.
Replace boiler B in a few years time.
Downside is we will always have 2 boilers to maintain.
Downside is it is not good practice to have one condensing boiler with one non-condensing.
Downside is we will always be heating a whole tank of water for a small amount of hot water for the kitchen tap and sinks as the bathroom it serves is hardly used.

Option 2
Replace Boiler A now with a combi boiler. Gas pipe to it is only 15mm and current regs mean that will need updating to 22mm.
Replace boiler B in a few years time.
Downside is we will always have 2 boilers to maintain.
Downside is it is not good practice to have one condensing boiler with one non-condensing.
Is it good practice to have 2 combis in the same property.

Option 3
replace both boilers now with one larger combi boiler.
Advantage, only one replacement to pay for. Only one to insure.
downside, anyone in a shower notices drop in pressure when another source is put on. At the moment the problem is avoided by eg using a toilet that isn't on that side of the house.
Disadvantage, the two current systems need linking. Not sure how good the service to 18 rads will be off one boiler.

Grateful for any opinions.

Generali

Can you change the shower to one which heats its own water?

I'd definitely be inclined to go down the single boiler road.

michaels

I would always use a system boiler rather than a combi, heat loss in storage tanks nowadays is minimal and you have much more energy available quickly for multiple, showers, hotting up bath etc plus you need a smaller boiler overall - we have a veissman that modulates down to 4kw or less and only needs to go up to 20kw for our 170sqm 4 bath house.

silvercar

michaels wrote: »

I would always use a system boiler rather than a combi, heat loss in storage tanks nowadays is minimal and you have much more energy available quickly for multiple, showers, hotting up bath etc plus you need a smaller boiler overall - we have a veissman that modulates down to 4kw or less and only needs to go up to 20kw for our 170sqm 4 bath house.

The one hot water cylinder we have only serves the main bathroom and can only support one shower and then not for too long.

can't have a megaflow as that would need a new larger water supply pipe and that is not accessible for various reasons.

michaels

silvercar wrote: »

The one hot water cylinder we have only serves the main bathroom and can only support one shower and then not for too long.

can't have a megaflow as that would need a new larger water supply pipe and that is not accessible for various reasons.

Mega flow would be best option but as you say, requires decent water pressure and flow rates. However you could still have a traditional vented system with a decent sized tank - I think ours is about 190l at 60 degrees and replenished at 20kw gives us pretty much non-stop hot water - we have certainly never run out.

silvercar

michaels wrote: »

Mega flow would be best option but as you say, requires decent water pressure and flow rates. However you could still have a traditional vented system with a decent sized tank - I think ours is about 190l at 60 degrees and replenished at 20kw gives us pretty much non-stop hot water - we have certainly never run out.

Our tank is 100l and there is no room for a bigger one and it is not sited anywhere the bigger single boiler could go.

Plumber90

I think your best bet is to get someone out to have a look. Much easier than fiving advice over a computer.

fezster

The main question is - do you need independent control of your two heating zones (i.e. the 14 rads and the 4 rads)? If the answer is no, then a single boiler makes sense. However, a combi (as you rightly say) means that if someone uses another hot water outlet, your shower may go cold. You can get combis with storage tanks, which can alleviate this problem somewhat. I'd look to get your mains flow and pressure tested to see if an unvented cylinder is suitable. With multiple showers, this is the best option.

If the answer is yes, then the problem is more complex. Having a single (large) boiler running 2 zones, especially where one is much smaller than the other, is problematic. You can range rate the boiler, but it has to be able to cope with a small zone (4 rads), large zone (14 rads), and both zones (18 rads). In my experience, Vaillant boilers do not cope well in this situation, and Im sure other manufacturers' boilers are the same.

silvercar

fezster wrote: »

The main question is - do you need independent control of your two heating zones (i.e. the 14 rads and the 4 rads)? If the answer is no, then a single boiler makes sense. However, a combi (as you rightly say) means that if someone uses another hot water outlet, your shower may go cold. You can get combis with storage tanks, which can alleviate this problem somewhat. I'd look to get your mains flow and pressure tested to see if an unvented cylinder is suitable. With multiple showers, this is the best option.

If the answer is yes, then the problem is more complex. Having a single (large) boiler running 2 zones, especially where one is much smaller than the other, is problematic. You can range rate the boiler, but it has to be able to cope with a small zone (4 rads), large zone (14 rads), and both zones (18 rads). In my experience, Vaillant boilers do not cope well in this situation, and Im sure other manufacturers' boilers are the same.

I don't need separate zones, we inherited 2 boilers because the previous owner built an extension and just put a new boiler in the extension rather than integrating the whole house into one heating system.

I think your best bet is to get someone out to have a look. Much easier than fiving advice over a computer.

I get that. The problem is distinguishing between salesmen wanting the work and doing what is best.

phil24_7

Personally I would go with 1 system and find the system that best fits your needs.

HappyMJ

For such a large property with multiple demands for water I really would not consider a combi boiler.

But that's my view. I like the smaller quieter boiler with instant hot water at very high flow rates. I also like that I have hot water using an immersion element when the boiler isn't working so need ever to call an emergency engineer. It'll mean losing the airing cupboard to put the bigger cylinder in so the water doesn't run out as you've described. 100 litres is too small.