I have a Potterton Performa 28i boiler with a top up valve fitted below it. The boiler constantly increases in pressure to about 3.5bar. I have bled all radiators and even bled the main outdoor valve. There appears to be no air in the system and the top up valve is switched off. HELP!
I'll bet a crisp fiver that the top up service valve is not as switched off as you think it is. This is not uncommon - it only needs to be open the tiniest little bit and with 50 (or so) psi mains behind it up goes your pressure. Alternatively it could be faulty.
Another distinct possibility is the pressure vessel throwing it's legs in the air.
Too high pressure for too long will start blowing some joints or damage the boiler. Let some out - CH must have a drain valve somewhere. Fix it soon.
I think you should get someone in for a boo at it.
I know you've already said it is, but firstly ensure the filling loop is turned off. And should be disconnected and blanked according to water regs.
Sounds like a fault on the pressure vessel, or plate heat-exchanger leaking.
You can test this by turning off the cold water to the boiler and operating the heating, set pressure at 1.0 bar if the pressure rises alot (it will rise abit around 0.5 - 1.0 bar) then it's the pressure vessel at fault.
If the pressure is rising when the boiler is not being uses, then it's probably the plate heat-ex at fault.
How old is your boiler ?
The pressure will only go to 3.5 - 4.0 bar, then the pressure relief valve will open.
Both of you are spot on. It seems the top up valve was not completely off. I drained more water out of system down to 1.5bar and adjusted the valve. It is now sitting at 1.8 and dropping to 1.5. Thanks to you both. Well done.
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