expansion vessel in combi boiler not coping..

[Dave£]

The central heating system I installed in my house has worked fine for

5 years or so. Then, last sumer, I installed a larger radiator in one of the rooms (a double rad, measuring 6' x 18" approx. Since then, the expansion vessel in the boiler has stopped coping with the expansion of the heated water. I think the new rad is the problem, beccause if I isolate that rad, the boiler works ok, and water pressure is sustained. If I un-isolate that rad, and fill the system to 1.25 bar, it blows water out of the relief valve as oon as it gets hot, and then the guage on the boiler soon reads 0 bar, and the boiler starts making a sort of moaning noise, kinda like an incoming 18" shell from a battleship, just before it hits you. (At least that's wht my vivid imagination cooks up). As soon as you increase the pressure ot above 1 bar, the noise stops.

I guess the solution is (a) to switch back to a smaller rad, or (b) to fit a larger expansion vessel. Do you agree?

Does anyone know if a larger expansion vessel can be fitted to a Britony 80 combi boiler, and if so, how much one costs, and is it an easy job to fit it? I'm a bit woried by the manual which says the expansion vessel is part of the boiler's chassis.

Thank you, Jake

[John Rumm]

How about (c) fit an additional expansion vessel?

Assuming your current one is working fine and has not lost air pressure, it sounds like the volume of water in your system with the bigger rad is too great for the size of vessel built into the boiler. The simple solution would be to fit another one somewhere else on the system. They are not that expensive as a stand alone item.

[Christian McArdle]

Yes, although there is no need to remove the old one. Just stick an additional one on in a convenient location.

Leave the built in one alone. An additional expansion vessel will cost a few tens of pounds and is easy to fit. Indeed, I would regard it as a particularly suitable project for someone interested in learning a bit about plumbing. It can be installed just about anywhere on the system, but preferably not zoned off.

Christian.

[Dave£]

Thanks John and Christian. It's good to learn that stand-alone expansion vessels are available. I didn't know they existed before you enlightened me. I'll try to source one.

Dave

.

[Ed Sirett]

See FAQ. I expect the existing unit has failed. Adding a new one elswhere _may_ be the easiest course of action. Sub-£50 certinaly for all the bits probably sub-£30.

[John Rumm]

Try:-

smallest is under 15 quid.

[Dave£]

Thanks John! All I need to do now is determine what size I need...

Dave

[John Rumm]

Assuming that the first one in the boiler is working OK, then then smallest will do since you are only "one radiators worth" of water over what it can cope with.

[Ed Sirett]

Assuming that the one in the boiler is dead or dying then the same size again. Likely 10 litres (could get away with 8 for a small [1] system).

[1] I mean numbers of radiator ==> low volume of primary circuit.

[John Rumm]

Assuming you don't know whether the one in the boiler is dead or alive, go for one big enough to cope with the whole system, since too little expansion room is a problem, whereas too much is not. ;-)