Loft mounted boiler?

After 26 years, it’s probably a good time as the weather improves (!) to retire our trusty Potterton Suprima 80 gas boiler. Apart from some control unit issues a few years back, sorted after i replaced a couple of tired looking electrolytics and reflowed the relay solder joints on the PCB, it’s been a decent boiler. It’s a fairly simple system, with a hot water tank and a two zone S-Plan system with Honeywell CM series programmable stats.

No interest in heat pumps, so we’re looking to get the gas boiler and pump replaced, system flushed, stats replaced - the Honeywell CM’s are great but one is having display issues.

Ahead of getting quotes, one issue I can see is the gas supply pipe. It’s a 15mm pipe which i’m assuming would need upping to a 22mm pipe. Unfortunately the gas meter is on the opposite side of the house to the boiler, so any new supply pipe would need to run between the boiler in the utility room and the gas meter which i assume would mean an outside run of new pipe between boiler and gas meter ?

The other option i can see here is a relocation of the boiler - if it went into the loft then it’s a simple run down the outside wall for the gas supply pipe to the meter and the water pipes, control cables can run along the loft and down into the airing cupboard to where the pump, diverter valves etc are located. Condensate run is also simple here into one of the bathroom soil pipes.

Apart from access for maintenance etc, are there other downsides to locating the boiler in the loft (if we need to go for that option) ?

Some thoughts, having had a new WB Highflow 400 installed a year or so back (on a L4L basis):

1- neighbour has a condensing wall-mount in loft and no issues, save for the obvious pipe runs – I think feed piping upgrade needed, as you say.

2- system flush - a subject of enquiry with my installer as, it seems, some manu’s dictate a power-flush for warranty qualification. With much of my pipework hidden, I didn’t want this and a simple chemical flush-out was agreed – helped as my piping and bleeding showed ‘clear’.

FWIW, my new boiler casing runs far cooler than previous model (c.2004). I’ve effectively lost a rad in the kitchen!

3- external condensate pipes – the simplest, shortest path is the best, obviously suitably spec-ed to prevent freezing, with access to a mains drain/or a ground pot (filled with chippings).


Our boiler is in the loft and we have not had any issues and it is serviced annually. The only downside Is that the boiler replaced last year did create noise in the spare bedroom below. The replacement is pretty much silent.

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Perhaps one thing to check on is whether/how you will manage any settings changes e.g. most boilers have an Eco-setting for HW now – how this would work for you/whether you’d need to go anywhere near it? You’d still need to keep an eye on the pressure gauge of course.

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When I installed a new boiler for my sister-in-law some years ago, changing the system from conventional to combi, I pondered the best place and based on the layout of the house suggested the loft (directly above tge batgroom), instead of the kitchen where the previous boiler had been, that way freeing up kitchen space, and minimising noise. They were a bit nonplussed at the thought, and nobody they or we spoke to had ever come across one situated there. But it’s made every sense for multiple reasons, so that’s what I did. The Gas Board person who came to check the gas pipework before connection was somewhat taken back at having to go up the loft ladder (a proper pulldown one) but was quite happy with it. That was maybe 20-25 years ago, and when they needed a new one a few years ago they had it fitted in the same place. It’s never been a problem being located there.

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I am a gas safe Engineer.
No problem having the boiler in the loft .
My boiler is in the loft . With the cyinder .
As long as you have a purpose built ladder.
The loft is boarded out to the boiler .
As long as your exsisiting boiler is nor open vented then you should be good :+1:

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My heating engineer has his in the loft and his house all plumbed with 22mm piping. :+1:t2:


I would so it just to get the ugly lump of metal somewhere you don’t have to see it, if possible.

Do you have a suitable wall to mount it, or joists that are strong enough to support the weight? Many joists are only intended to support the plaster ceiling beneath, although mine is still capable of supporting a 250 litre tank and loads of other stuff.

How noisy will it be? If it’s above a bedroom it will need to be very quiet. Manufacturers quoted noise levels are usually based on lab. measurements. Noise in an enclosed space may be higher, in addition to any vibrations transmitted through the structure.

Make sure any controllers are accessible. I’ve had installers put switches, isolation valves, controllers etc. in the loft because it’s quick and easy for them instead of in a convenient ground or first floor location.

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It might be worth getting somebody to check if the existing 15mm gas pipe is large enough.

Presumably the pressure at the existing boiler can be checked.

A conventional (non combi) boiler might be OK, as it’s not providing instantaneous heat for the DHW.

With regards to installing a boiler in the loft. My father in law had a boiler in his lost, which was fine when he was an agile 80 year old, when he got into his 90s, he struggled getting up and down to the boiler. He was obviously told not to go in the loft, but very rarely listened to advice. :flushed:

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Yes, I missed that: I very much doubt 15mm would be large enough. IIRC the boiler I installed in a loft used 22mm, though it might have been 28. (Its a long time ago and I’ve only done oil since) A combi will need bigger than a ‘system’ boiler.

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We have a Vailant boiler in the loft. It is supposed to be a certain distance from the hatch opening, but ours isn’t. But on the other hand the engineer can stand on the loft ladder and get at it easily. It’s fixed to a piece of plywood fixed between roof and loft floor joists. It’s all worked out fine.

The gas pipe was a slight faff because the pipe went through an inaccessible place as 15mm but as all of the rest was already, or could be, changed to 22 mm, that worked out ok. The condensate drain was a bigger faff because they ran it into a pipe that picked up the drain in our bathroom, but the condensate seems to age plastic quite fast and I have had to replace a complicated piece of piping three times, the last time because a heavy cat had fallen off the washbasin and broken the pipe comprehensively :scream_cat:

Anyway overall it was the right place to put it, but if I were replanning the house from scratch, I wouldn’t put it there!

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I’m guessing another factor would be other gas appliances in house.

Gas oven/rings and gas fire all turned on full could cause reduction in pressure at boiler, making 15mm unsuitable.

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I think that would depend on where things ‘tee off’, larger pipe before.

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Morning all - I thought i’d get some useful responses from posting here and appreciate all the replies to my question. I’d rather the new boiler stays in the same location, but just wanted to check if there were any significant downsides to a loft location if we need to explore that route, which from the responses seem to indicate not :+1:

Thanks again.


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That shouldn’t happen because the gas supply is at a higher pressure in the supply pipe and regulated at the point the gas leaves the meter. But of course it does still require the house to be piped with 22mm pipe to the point where other things are connected.

The issue with 15 mm pipe to the boiler is that the maximum gas that can be delivered over 15mm is quite limited and most modern boilers are sized for at least 22mm. For example our Vailant which was sized to supply a four bedroom house with a tanked hot water supply specifies that a 22mm supply pipe must be used but up to a metre of 15 mm pipe is permitted where the pipe connects to the boiler.

Our plumber bought my suggestion that the 200 mm of 15 mm being allowed to remain implied by not pulling the house apart to replace the existing 15mm pipe could be anywhere in the length of 22mm pipe and didn’t need to be at the end by the boiler.

Isn’t is strange how our inefficient 1970 boilers were quite happy using 15mm, but now our ultra efficient 2024 boilers which use less gas now require 22mm.

One thing I would say, is check that the new boiler is correctly sized. It is very common to oversize Gas Boilers, because whilst a little more inefficient, it generally doesn’t cause any problems that the user will notice (IMO).

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When we had our boiler fitted in the loft, I got a quote from British Gas and a quote from an independent plumber who was a registered Vailant installer. I had worked out what size I thought we needed.

The independent guy agreed with me and quoted accordingly. British Gas said that the boiler I wanted was a two man lift and so they couldn’t fit it in the loft, but they could fit in the loft one size of boiler down which they thought “would do”.

British Gas were about £1000 more expensive too, so I went with the. Independent guy. I asked him about the two man lift and he just laughed. I noticed that he had no problem getting it up there on his own, even though he had a mate doing work on the radiators at the same time, who could have helped if needs be.

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To be fair, the British Gas guys were probably trained to work within a risk assessment covering the Manual Handling and Work at Height regulations where an independent installer would be far more likely to fly under the radar.

A few years ago we got a phone call from the owner of an Indian restaurant in London, (we’d installed a gas fired hot water generator control panel a couple of years earlier).

The boiler kept switching off and the engineer Potterton sent to look at the problem diagnosed a control panel fault. I asked him a few questions and it turned out the boiler was showing an error code for low gas pressure. Presumably the Potterton engineer thought the control panel was closing the gas safety valve.

During further questioning he mentioned that recently two additional gas ovens had been installed in the kitchen.
I suggested he doesn’t use the boiler when all the ovens are working and he refuses to pay the £500 Potterton wanted for sending out an engineer.

We didn’t hear from him again.

I’ve just looked at a Baxi training video on youtube, advising what to do if low gas pressure error code displayed.
If other gas appliances are in the home, turn one of them on full, turn the boiler on full, and then check the gas pressure at the boiler.


A combi boiler requires more gas, as it’s providing instantaneous heat for the DHW.

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