Boiler size & cost

BohemianRhapsody

Hello. We need to change our old boiler and getting quotes. One of the engineers is recommending a Vaillant ecoTEC Plus 24kW High end Combi for our 4 bed 2 bath house (15 radiators). He is worried that the bigger size, i.e. 30kw, might cause issues with the pipes (currently 22mm) which would need changing to 28mm. I am unsure as when I do online sites, the suggestions are 30kw or even 35kw boilers. In addition, the quotes are coming higher than expected, just under £4k (London) and we are not changing the location of the boiler, although they have to do a flue to the roof. This includes the usual power-flush, filter, nest etc. The other option is to go for a cheaper alternative,  Vaillant EcoFit Pure 825, which comes to £3,300 but again, not sure if it's the right choice. Many thanks.  

Jeepers_Creepers

Has the plumber tested your mains flow rate and pressure? Do you know what they are?

Do you currently have a combi, and do your taps (cold) 'gush'?!

Ok, this is hard to say, and I hate saying it, but your plumber is a twit. He has got two of the most basics issues to do with combi boilers completely wrong.

1) With a combi, size is everything. Unless you live in a one-bed flat, you'd be insane to fit only a 25kW model. Bonkers. The flow rate is directly connected to the power rating, and 10lpm is pants. When you say you have a 2 bath house, do you literally mean baths? If you do want to fill even the occasional bath, 25kW will lead you to distraction; it'll be painful. Do you like showers? Do you like good showers? Ditto - the difference betwixt a 25 and 30kW is significant and very noticeable. No plumber should be recommending a smaller boiler.

2) Pipe size. You have 22mm pipes? Oh dear - they are too BIG. AAaaarrrhggghh - (realisation) - is he talking about the GAS supply pipe or the plumbing pipes? I'd first assumed 'plumbing' but now suspect it's 'gas'? In which case, I take back my insults...

Ok, yes, depending on how long the gas pipe run is, and how convoluted, you may well need to go up to 28mm for the larger boilers. This isn't rocket science, it isn't guesswork - it is easily calculable. I should know, 'cos I have dun it - and I'm a DIYer.

(If he's talking about the water pipes, then he's still an idiot, but I won't go there...)

To replace the gas pipe will undoubtedly cost a fair bit more, probably a £ew £undred. Personally, I would never ever ever have a combi below 30kW power, and would go for 35kW whenever possible (My current one is 30kW and is absolutely fine, but I wish it was slightly better :-)  )

So you need to get more quotes, I suggest, which will include the possibility of requiring a new gas pipe from your meter to the boiler. Can you give us an idea of the distance, and how many corners the pipe goes a round? And is anything else gas in your house - hob, etc? 

Rosa_Damascena

If you have a tank then why not consider a standard boiler? 24kw will do and I would imagine the price would come in at <£2k.

BohemianRhapsody

Many thanks for your replies.
Jeepers - Thank you for the detailed answer. It's one bath & one shower, 22mm is the gas pipe. Our current Vaillant boiler is 20 years old and I think is 30kw. He did test the water flow is 20l/minute I think. Does that sound right? Our current water pressure is good. We like hot showers with good pressure. So you think minimum 30kw and if needed be, change the gas pipes to 28mm and pay the few hundred? I am not sure how long is the gas pipe and how convoluted, but the gas meter is on the ground floor, and the boiler is on the second floor. 
Rosa - we have a combi so no tank.

daveyjp

20l a minute is excellent, certainly enough for a 30-35kw boiler.  Test it yourself.  Turn a tap on full (usually kitchen) and time how long it takes to fill a 1 litre container.

Vaillant do a 38kw combi which is good for 16l of hot water a minute.

Jeepers_Creepers

BohemianRhapsody said:

Many thanks for your replies.
Jeepers - Thank you for the detailed answer. It's one bath & one shower, 22mm is the gas pipe. Our current Vaillant boiler is 20 years old and I think is 30kw. He did test the water flow is 20l/minute I think. Does that sound right? Our current water pressure is good. We like hot showers with good pressure. So you think minimum 30kw and if needed be, change the gas pipes to 28mm and pay the few hundred? I am not sure how long is the gas pipe and how convoluted, but the gas meter is on the ground floor, and the boiler is on the second floor. 
Rosa - we have a combi so no tank.

Cool, BR - that sounds promising.

30kW is 30kW in anybody's money, so hopefully the current 22mm pipe will be good for a modern 30kW boiler too.

30kW is fine - that'll give you really nice showers (as I can testify). Whether it's worth increasing this to 35kW with the possible associated extra cost of renewing the gas pipe, that has to be your call. I think I'd say, if you were happy with the performance of your old boiler, you will surely be happy with the new one of the same rating - but which will be more efficient, and this will almost certainly mean a better transfer of energy to the water = a bit more flow (it should be possible to look up the spec of your old one to compare!).

I presume you will be getting at least one other quote? If so, ask them to price for both - 30kW and 35kW - and whether the gas pipe will need upgrading. (It's a very simple formula - basically how many metres of pipe, how many bends and elbows, what other calls are there on gas and where this will 'tee' off the pipe, etc. Basic 'rithmetic. Most GasSafes, tho', have a quick look and determine that '22mm will do...') Armed with 2 quotes, you make your call. If the guy is certain - and can show on the back of his fag packet - that a 35kW will be fine on the existing pipe, then I would personally go for this.

Is your boiler located roughly above the gas meter?

fezster

What's wrong with your current boiler? Has it broken down and uneconomical to repair?

BohemianRhapsody

daveyjp said:

20l a minute is excellent, certainly enough for a 30-35kw boiler.  Test it yourself.  Turn a tap on full (usually kitchen) and time how long it takes to fill a 1 litre container.
Vaillant do a 38kw combi which is good for 16l of hot water a minute.

Thanks, will did test it, and it looked like 14-15l a minute. I did it in the kitchen, he did it in the garden tap. So I think 35kw probably the max capacity. 

BohemianRhapsody

Cool, BR - that sounds promising.

30kW is 30kW in anybody's money, so hopefully the current 22mm pipe will be good for a modern 30kW boiler too.

30kW is fine - that'll give you really nice showers (as I can testify). Whether it's worth increasing this to 35kW with the possible associated extra cost of renewing the gas pipe, that has to be your call. I think I'd say, if you were happy with the performance of your old boiler, you will surely be happy with the new one of the same rating - but which will be more efficient, and this will almost certainly mean a better transfer of energy to the water = a bit more flow (it should be possible to look up the spec of your old one to compare!).

I presume you will be getting at least one other quote? If so, ask them to price for both - 30kW and 35kW - and whether the gas pipe will need upgrading. (It's a very simple formula - basically how many metres of pipe, how many bends and elbows, what other calls are there on gas and where this will 'tee' off the pipe, etc. Basic 'rithmetic. Most GasSafes, tho', have a quick look and determine that '22mm will do...') Armed with 2 quotes, you make your call. If the guy is certain - and can show on the back of his fag packet - that a 35kW will be fine on the existing pipe, then I would personally go for this.

Is your boiler located roughly above the gas meter?

Thanks. I just got a new quote. Option 1 Vaillant EcoFIT 830 Pure boiler  £3,090, or Vaillant 832 Plus for £3,500. Both 10 years warranty. Yes the boiler is located roughly above the gas meter, the gas meter on the ground floor while the boiler on the second. So the pipe might not have many bends, but as you say, that's just a guess. 
The extra complication is that we are planning to potentially get a Megaflow system in 2 years time if we manage to build a utility room on the ground floor but apparently the combi can be converted into a system boiler connected to the Megaflow, so we wound't lose money. 

BohemianRhapsody

fezster said:

What's wrong with your current boiler? Has it broken down and uneconomical to repair?

8 weeks ago it started loosing pressure. I need to increase it every week or so. Also, it's what they call 'cycling', i.e. it gets to a certain temperature and then goes down to protect itself from overheating. Apparently something to do with dirt in the boiler. They couldn't service it because of that as couldn't measure the gas flow I think.  One gas engineer recommended us changing the pressure valve (cost ca £120 including the part) and see if this sorts out the pressure issue, but he said that it could also be a leak on the system. He thinks that if fixed, the boiler could get us through another year or 2 until we have the utility room ready so we can then install directly the Megaflow system, saving money. I am hesitant as keep throwing money on an old boiler doesn't make sense but on the other hand, it might be worth trying. 

Jeepers_Creepers

BohemianRhapsody said:

Thanks. I just got a new quote. Option 1 Vaillant EcoFIT 830 Pure boiler  £3,090, or Vaillant 832 Plus for £3,500. Both 10 years warranty. Yes the boiler is located roughly above the gas meter, the gas meter on the ground floor while the boiler on the second. So the pipe might not have many bends, but as you say, that's just a guess. 
The extra complication is that we are planning to potentially get a Megaflow system in 2 years time if we manage to build a utility room on the ground floor but apparently the combi can be converted into a system boiler connected to the Megaflow, so we wound't lose money. 

That sounds good.

Are you generally happy with the performance of your existing boiler, or have you been left feeling you'd like a 'bit more'? If 'happy' then go with the 30kW. If you want a bit more, then you know what to do - go 35kW.

Almost certainly, from what you describe, the existing 22mm gas pipe will be more than ok with either, and even more.

If you are planning 'mega' later on, and if it's been confirmed that either combi will be fine to use as a 'system' boiler, then perhaps stick with 30kW, 'cos the extra 5kW will just not be needed.

EcoFIT versus EcoTec 'Plus'? Now, that's the 6 million dollar question! Wanna know the difference?

Me too. (Let me know when you find out)

What I WOULDN'T do, is go 'plus' and only 2kW more. What's the point for £400? First decide on power - 30kW or 35kW. Then chose the model - Eco or Tec. Once, of course, you find out the bludy difference betwixt them :-(