New Boiler, and 15mm pipe?

[chrisdicko]

Am I right in thinking that a 15mm gas pipe going in to a combi boiler is illegal now?

Just my current 20 year old (ish) combi boiler is on its way out, and I need a new one. One plumber came round, and didnt check the existing pipework, and quoted £1700 which I though was far too much for a straight (ish) swap, even he said it wouldnt be too hard to do.....except maybe the flue to the roof, as its high.
The second plumber came, and checked pipework, pulled the washer etc out, and he said that there is 15mm pipe going in to the boiler which is now illegal. Plus wouldn't give me the required flow of gas, which I'm not sure he's right as at the moment I can have the cooker on, run a bath, and have the heating on with no problems. He checked the meter which is two grounds below, and said it starts in 22mm, so obviously changes to 15mm at some point. Its going to be a real pain taking the carpets and floor boards up, especially as its communial stairs etc.

Is there an easy way round this, or is he being a good plumber?

Also, as a rough estimate if you dont mind from the plumbers......how much for a new boiler for a 1 bed flat, with 4 rads. I thought maybe £1200ish, but the 1st quote I got was for £1700 which seemed quite steep.

 

[DP]

I would suspect the boiler will need 28mm pipe let alone 22 depending on number of bends on the gas line.

Your present boiler does not have to work hard to heat water. A combi needs power to heat water instantaneously, therefore a correctly sized gas line. Undersize it and your boiler will not only not give you hot water at the temperature it is set for, cooking while asking for hot water will effect cooking too.

Go for heat only boiler. Gas line may then be possibly correctly rated.

 

[kirkgas]

couple of things from your post, i won't comment on a price of £1700 being too expensive as i have not see the job, but you say you can cook, run bath and have heating on at the same time so you think your gas pressure is ok, with a combi hot water has priority over heating even when on at the clock so you will NEVER have heating and hot water on at the same time, the clock will be on but will only go through rads when you shut tap, again without checking i can't comment if gas pressure at boiler is satisfactory while you have cooker on, but i will say the potential for a problem lies when you are cooking and then run a hot tap, IF the gas pressure is borderline there is a chance the cooker might be starved of gas and go out while the tap is running, when you close the tap the unburnt gas will flow through the cooker.
you also said the gas pipe will be awkward to change as it is in a communal stair, if a gas pipe goes through a communal stair i think it should be MI pipe, (although you seem to be saying it is under stairs, so this will need clarified)

 

[mickyg]

Just my current 20 year old (ish) combi boiler is on its way out

what are you 2 on about?

 

[chrisdicko]

Thanks for the replies.

DP, what do you mean? I have a combi at the moment, and it runs ok (for its ages etc).

kirkgas, I've tried having all four rings, the oven, heating and running hot water, (although like you just said the heating wont be on when the hot water is) and there is never anything wrong.
The plumber did mention maybe having to change some pipe at the meter to 28mm. I dont know what M1 pipe is to be honest. But Im sure the pipes run up the wall in a box, then when it gets to my floor, it goes under the floor boards (i think) in to my flat....this is where the plumber thinks it might change to 15mm.

 

[mickyg]

to answer the question. Your gas pipe may well be adequate if you size the new boiler the same as the old one. There is still a chance it may not be suitable due to the way new boilers operate, but there's a fair chance it may be fine. 1200 is unrealistic for a good boiler and a quality installation job, but then maybe you don't want that............

 

[chrisdicko]

Oh, I do

Just dont want to be ripped off really. As the 1st quote I had, he named the boiler, so i googled it and it came out at £800....so he wanted £900 labour for a day (he said it would take a day).

Having a quick read, it seems its illegal to use 15mm pipe now? So the floor boards will have to come up and be changed to 22mm what ever happens?

 

[mickyg]

Its not illegal, thats nonsense. If you have no more than a 1mbar drop from the meter in working pressure at your shiny new boiler then it does not matter what the size of the pipe is. It is true that quite often 22mm pipe is required to obtain this, but in my experience if you have a 28kw combi with the correct working pressure and replace it with another 28kw combi there's a reasonable chance it will be fine.

 

[chrisdicko]

Oh right, Im sure the plumber said it was against the regs......20years ago it wouldnt matter, but he said it would now. So if he tested the pressure and it was ok, he wouldnt have to changed the pipework?

 

[tonybhoy]

Oh right, Im sure the plumber said it was against the regs......20years ago it wouldnt matter, but he said it would now. So if he tested the pressure and it was ok, he wouldnt have to changed the pipework?

Yep. But if he fits the boiler and the WP is no good then'll he'll have to change the pipework. Sounds to me that you will need it replaced.

I'm now increasingly replacing 22MM with 28MM pipework these days ,mind you I'm fitting 37 & 42 KW boilers although having said that I fitted a 37 KW boiler to an existing 22MM gas supply of about 6mts recently and the WP was borderline.

A 30KW boiler requires 3.4M3/hr of gas. Twelve mtrs of straight 22 MM pipe with no bends discharges 3.9M3/hr so a 28KW boiler will be slightly less at say 3.0M3/hr but 20mtrs of straight 22MM pipe can only discharge 2.9M3/hr of gas.

Each elbow adds 0.5 mtrs to the length of the pipe so 10 elbows will add another five mtrs to the pipe and this reduces the gas discharge to 2.5M3/hr.

 

[chrisdicko]

Yeah, its quite a long run, with quite a few bends to be honest.

There is a valve one the 15mm pipe, just before it enters the boiler. Could he test the flow there or wouldnt it work really?

I agree though, sounds like it might be a bigger job than I expected.

 

[tonybhoy]

Yeah, its quite a long run, with quite a few bends to be honest.

There is a valve one the 15mm pipe, just before it enters the boiler. Could he test the flow there or wouldnt it work really?

I agree though, sounds like it might be a bigger job than I expected.

He needs to check the WP (working pressure) with the boiler working on hot water,i.e. full demand and all other appliances on at the same time.

He can use the old boiler but that will only tell him about that boiler not the new one.

Tony.

 

[Agile]

He can use the old boiler but that will only tell him about that boiler not the new one.

Tony.

Yes, but knowing that he can calculate what the pressure loss would be with a different powered boiler.

Tony

 

[tonybhoy]

He can use the old boiler but that will only tell him about that boiler not the new one.

Tony.

Yes, but knowing that he can calculate what the pressure loss would be with a different powered boiler.

Tony

True

 

[mickyg]

He can use the old boiler but that will only tell him about that boiler not the new one.

Tony.

Yes, but knowing that he can calculate what the pressure loss would be with a different powered boiler.

Tony

True

and so back to my original point that if you replace a 28kw combi with another 28kw combi there's a fair chance it will be fine, especially bearing in mind that the input will actually be lower on the new one.