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ok.. So got called to this boiler as it was losing pressure, firstly checked for any leaky pipes / rads and nothing appeared at fault. Then inside the boiler on closer inspection i noticed that the manifold pipe around the pressure switch prv was slightly weeping and quite a large ball of limescale had built up around this area. Rather than just mearly cleaning the area i replaced the manifold pipe and re pressured the system and left.
6 weeks later i get a call again to say it has lost some pressure again, i am now thinking of replacing the expansion vessel as there is not much else on the circut. The boiler in question is a firebird combi. does anybody agree or have anyother suggestions as to where the pressure could be going.
Cheers alex
 
The low presure switch on these leaked and the o ring was changed to a red one because the black ones werent man enough. You dont say how old the combi was.
All combis always leak eventually thats why I always recommend and unvented cylinder and boiler. I wouldnt touch a combi with a barge pole and I certainly wouldnt fit one in my house.
Luckily most combis that are fitted now you can get a 5 yr warranty for.
I take it you have checked the expansion vessel for charge and that the prv is not letting by, also check that the Exp vesel hose is not blocked
 
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I'm surprised you did not check that the PRV was not leaking when you checked the rest
of the system.

Press in the valve on the vessel and if water comes out then it is knackered and needs
replacing.

Check the pressure in the expansion vessel when the rest of the system is at zero pressure.

Top up pressure to about 0.8 bar or whatever the manufactures instructions advise.

If the PRV is letting by (dripping) then this could very well be the problem.
 
The low presure switch on these leaked and the o ring was changed to a red one because the black ones werent man enough. You dont say how old the combi was.
All combis always leak eventually thats why I always recommend and unvented cylinder and boiler. I wouldnt touch a combi with a barge pole and I certainly wouldnt fit one in my house.
Luckily most combis that are fitted now you can get a 5 yr warranty for.
I take it you have checked the expansion vessel for charge and that the prv is not letting by, also check that the Exp vesel hose is not blocked

Hi Kimbo, thanks for the reply, i also replaced the pressure switch and prv so both new and checked. I did check the exp vessel and seemed to have charge, but not ruled it out ! It belongs to a housing estate, so know they wont put a new system in on the basis that all combis leak. Im sure that i saw something with 2007 on it last time i went as an indication of age
 
I'm surprised you did not check that the PRV was not leaking when you checked the rest
of the system.

Press in the valve on the vessel and if water comes out then it is knackered and needs
replacing.

Check the pressure in the expansion vessel when the rest of the system is at zero pressure.

Top up pressure to about 0.8 bar or whatever the manufactures instructions advise.

If the PRV is letting by (dripping) then this could very well be the problem.

Hi, yes i did check prv . was replaced as part of the manifold. No water came from the schrader valve on the expansion veesel when i checked pressure,, seems to have been an ongoing problem for over a year now, just my look i get the maintenance contract and get lumbered with this !
 
went today, pressure in CH was down to around 0.5 BAR so drained off the excess pressure and got my little gauge and tested the expansion vessel, IT didnt even reister.....flat as a fart. Was going to replace it as part of caution but not a stock item, up to 10 days delivery and just a squueze over £100 for vessel and connecting hose, NO THANK YOU! so got out my foot pump and jacked it back up to 1 BAR. Tested no water leakage by releasing a little. Waited 20 min or so then re check, still got its pressure so top up water and away she goes. Lets see how long it lasts ! Hopefully cured it.

I obviously didnt check it properly the 1st time !!
 
Also check the hose between the vessel and the boiler - I have had these get blocked with debris. Push a screwdriver into the hole in the boiler to check.

If the vessel loses pressure again, take the Schrader valve out of the Expansion vessel and fit a new one (or ask Kwik Fit to do it for you), sometimes they leak from there, rather like a car tyre.

Generally when this happens with Firebirds (yes it always seems to be Firebirds I have problems with) I recommend a strip down and replace all the seals, washers and gaskets on the boiler. Takes about 4 hours but at least you go through everything.

The washers they use on the heat exchangers are really poor and I often find these are a source of leaks. The pump valves are the screwdriver in slot types and those leak too so they get replaced.
 
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