Combi boilers with 15mm gas inlet valve

[trevorbayliss]

I have an ariston combi which is coming up to 15 y/o. It works, but has been a pig of a boiler due to a design fault. This was finally sorted out 7 years ago. Prob a well known issue so won't go into it.

Anyway i am looking at boilers to replace it.

Has to be cheap to mid range. £500-600 is a good price for me.

I have spoken to my engineer and he says to use the Ideal instinct because it is set up to take the 15mm gas feed and not 22mm. We do have a 22mm gas feed near the boiler on the ceiling (joisted ceiling in cellar and so all accessible) which changes down to 15mm.

So we could go back to 22mm easily, but using what we have is quicker and easier.

So are there any other boilers i could use are do i get the ideal. OR would it be better to swap the reduced section of copper for the full 22mm?

 

[Gasguru]

Get yourself another "engineer" the guys a clueless muppet.
Gas regulations (the law) dictate the maximum pressure drop from gas meter to boiler...the inlet size on the boiler has absolutely no relevance.
Manufacturers often put a 15mm fitting on their boilers in order to save money.

It's quick common to find pipework of 28mm feeding combis where the pipe run is tortuous, larger domestic properties may have meter to house pipework of 50mm diameter....nothing to do with boiler inlet size.
Gas pressure is very low and to comply with the maximum pressure drop the pipework must be of appropriate size...straightforward calculations can be done to predict the requirement. During commissioning the pressure drop is checked.

What boiler have you got...Microgenus HE? The only real issue was the early recuperator design could be problematic, otherwise easy simple boilers to repair.
Given your Ariston was a cheap boiler and they are often poorly installed it would not surprise me if your existing gas pipework was undersized and will require upgrading.
Any length of 15mm feeding a combi will drop significant pressure.

 

[trevorbayliss]

The ariston has been fine all these years except for the air flow issue. So eventually a restrictor was removed and all has been good since.

The engineer is good and a mate. He wants to make life as easy as possible, hence not changing the 15mm piping. The house is tiny with 5 rads, so i don't think the sizing of the gas pipe is an issue.

The meter is in the opposite corner of the kitchen to where the boiler is. So the 22mm gas feed travels about 6m and then reduces down to 15mm and this runs for about 3m to the boiler.

 

[Gasguru]

There's a well known saying in the trade...never work for family or friends.
He knows full well what the requirements are and that the gas pipe is likely to require upgrading.
He wants an "easy life", really?

The house size is irrelevant (the maximum gas flowrate occurs with a hot water demand) but you're determined to make up your own rules to justify the bodge.
Just that section of 15mm pipe (including a few elbows) will result in the maximum permitted pressure drop let alone the rest of the gas carcass.
Your new boilers manufacturer will void the warranty if the gas pipe is incorrect, and of course you new building control notice (if he actually notifies) will be pointless.

 

[ianmcd]

As has been correctly advised the diameter of the gas inlet valve to a boiler means absolutely nothing regarding pipe sizing, some manus do specify a minimum size of pipe to the gas valve and I have seen clowns using smaller diameter pipe and then increasing it before the connection to the boiler

 

[muggles]

The engineer is good and a mate.

Sorry but if he's prepared to cut corners and ignore gas safety regulations "because it's easier" then he is neither of these things.

The house is tiny with 5 rads, so i don't think the sizing of the gas pipe is an issue.

Irrelevant. The size of the gas pipe must be calculated based on the gas requirements of the boiler when it is running at full power, not on how big your house is or how many radiators it has.

The amount of gas your current pipe can carry, and therefore what size boiler can be fitted to it (regardless of make) can be easily calculated. This calculation can then be used to determine whether the pipe requires upgrading or not

 

[fixitflav]

The amount of gas your current pipe can carry, and therefore what size boiler can be fitted to it (regardless of make) can be easily calculated. This calculation can then be used to determine whether the pipe requires upgrading or not

Agreed, but perhaps the OP's mate has already done that. If not he should ask him to.

 

[gasbusters]

Change the pipe to 22mm, gives you many more options. The Biasi advance boilers at about £500 are great, my boiler of choice although Main duo techs are also good, though aboit 650'ish

 

[ianmcd]

Quite acceptable in some circumstances.
Only a clown would suggest that a reduction in pipework diameter must be carried out downstream and not upstream.

Well you should know CoCo

 

[Gasguru]

Agreed, but perhaps the OP's mate has already done that. If not he should ask him to.

We've been given sufficient details about the pipe size/length to know it's undersized...his mate doesn't care.

 

[fixitflav]

We've been given sufficient details about the pipe size/length to know it's undersized...his mate doesn't care.

I can't see where he's given us the boiler rating hence gas maximum flow. If it's 24kW as one Ariston model I get pressure loss on existing just below 1mb, but it's down to the installer to confirm.