alpha cb28 combi problem

[loyd30]

Hi
looking for some advice on this boiler,its nearly 15 years old now & has had parts replaced in the past ie thermistors / divertor / sensors / & pressure vessel recharged etc but has developed a fault now when the ch is on sometimes the pressure rises very high, it normally sits a 2 - 2 1/2 bar but once went to nearly 4 bar & the prv never cut in & released any water outside (had some dripping from the inside though ) it also seems to lose pressure over a few days even though i cant see any leaks anywhere . any advice appriciated as to what the problem could be & is it worth spending money on ? heating & hot water fine except for that.
regards laurie

 

[Gasguru]

It should be around 1 bar when the radiators are cold.

 

[loyd30]

sorry meant to say that when its off & cold it sits at 1- 1.2 bar rising to 2 - 2 1/2 bar when on but occasionally reaches 3 - 4 bar

 

[ianmcd]

you have an expansion problem, could be the vessel, could be the communication hose/pipe, the leak was probably coming from the PRV outlet pipe before it went outside, you would be surprised how many leak as they are seldom tested when installed and there is only water in them when they actually operate

 

[terryplumb]

You also have a problem with the PRV ,if the system pressure gets to 4 bar and no water is released from the PRV pipework outside.

 

[loyd30]

Thank you for replies,had expansion vessel recharged today & all seems well so far but told that it might not hold its charge & if so will need a new vessel, but my boiler is in a cupboard & no rooom above to remove it plus flue goes through back wall so i would need a stand alone vessel fitted somewhere in the cupboard,can anyone reccomend a decent fair priced 8ltr vessel that would be suitable.
regards l

 

[ianmcd]

Wait untill you see if you need one, more likely the shraeder valve than the vessel if it could be re-charged