Boiler Replacement in BISF House Loft

Boiler Replacement in BISF House Loft 1

Hi all,

Just thought I’d share our BISF House boiler replacement project, because although I’m sure it’s been done before, I have not heard of anyone replacing the back boiler with a new boiler in the loft.

In my opinion there is no really satisfactory place for a new boiler in the house itself or the out-house. It can be put in the airing cupboard instead of the hot water cylinder but that takes up valuable storage space. The kitchen has limited cupboard space without taking up another cupboard with a boiler. The out-house is OK, but it’s away from the “core” of the house where the existing hot water and central heating pipes are, especially since the steel floor beams in the house run front-to-back which would make connecting it up awkward without a lot of surface-mounted pipes.

Therefore I have chosen for it to be mounted on the gable end in the loft, so it is out of the way and it can be fairly easily connected up to the HW and CH. They have drilled two of the steel stanchions on the gable and bolted an OSB board between them to mount the boiler on. It will then be vented out horizontally through a hole cut in the steel cladding. This means that when the roof covering comes to be replaced, it will be possible to remove the old flue and chimney altogether (flashing around chimneys is where roofs always leak, if they’re going to!).

I have already rerouted the HW pipe to the bathroom and kitchen as part of redoing the bathroom. Instead of connecting up the new boiler to the old pipes in the airing cupboard next to the HW cylinder, which would make a big loop and make it take a while for the taps to run hot, I have taken it straight down from the loft inside the wall between the landing/bathroom (via a shower) to connect up with the feed to the bath, handbasin and kitchen below. I have also put the condensate pipe in the by the same route, discharging to into the bath waste under the bath. This is so it doesn’t have to go outside where it can freeze and looks unsightly.

The CH flow and return pipes go across the loft from the gable to the airing cupboard where they will connect with the existing system, but I’ve taken the opportunity to T some 15mm branches off to a towel radiator in the bathroom and a radiator in the small bedroom (which never had a radiator).

The bathroom radiator is fed by pipes dropped down inside the landing/bathroom wall on the window side of the doorway. Previously it had a radiator fed by 8mm microbore pipes but these were deteriorating. I have put all the pipes under insulation boards and then a chipboard deck so they are protected from cold and out of the way.

The only pipework I haven’t done as I’m not qualified is the gas feed. The engineer is installing a complete new pipe back to the meter as the existing cooker feed is steel and cannot be easily connected to. The new gas pipe goes up inside the wall above the meter, but like the original pipe its path is blocked by the steel beam in the top of the wall, so it has to come out into the kitchen just below ceiling level. Then it goes into the ceiling/floor space where a floorboard has been lifted on the landing, then up inside the landing/bathroom wall to the loft.



  1. New hot water pipe from boiler in the loft to the bathroom and kitchen in the bathroom/hall wall, also put the lighting cables that were surface mounted in here. The white pipe is the condensate pipe from the boiler that drains into the bath/hand basin waste under the bath.

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  2. The only part of the new gas pipe that could not be put in the wall, because of the RSJ in the top of this wall. Copper pipe is the new one to the boiler, the painted steel one is original and for the cooker. I’m planning to hide them with full height kitchen cupboards.

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  3. Quick update as it’s all up and running and I’m very pleased with the performance. The hot water pressure is obviously a lot better than the old gravity fed system and the flow rate is better too (to get a good flow rate from a gravity fed system you really need 22mm pipe which we didn’t have). It does take a little longer for the water to run hot, so I’m glad I re-routed the hot water pipe to shorten it rather than just letting them connect it up where the hot water cylinder was in the airing cupboard.

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