Halstead Ace High - Pressure drops

[Frazz]

I've had problems with the pressure dropping in my system when the CH is running. Pressure remains constant with no heating on. Set it to about 1.5. After heating has been on, and cooled down again pressure has often dropped below one. Halstead suggested either that the pressure vessel may need repressurizing with more air or a faulty pressure relief valve. My money is on the PRV since when pressure gets to about 2.5 max (but only once in a while - usually stable at around 2 when CH is running) you get some venting of water from the system - pressure has never reached 3 which is what the valve is rated at. Plumber (good mate and honest guy) thought vessel might need topping up with air as well based on what Halstead had suggested. Anyway he managed to vent air from vessel rather than topping it up (!) and then wasn't too sure what air pressure it needed to be topped up to so guessed (!!). It was air that came out and not water suggesting the diaphragm is intact. Also cleaned out the PRV. Seemed to work OK, but now I'm getting water venting again as before. So a) do you reckon it's a problem with the PRV which needs replacing b) would a pressure vessel fault look like this c) what air pressure should the vessel have been topped up to and can you use the guage on the bolier to measure this or do you need a separate guage?
Cheers - Frazz

 

[Frazz]

Any suggestions? Any would do - am reluctant to go down the route of changing the pressure vessel unless I'm sure that it's faulty as this looks like a BIG job, but no-one I've talked to can suggest a way of diagnosing what exactly the problem is.

Cheers - Frazz

 

[Mikeyboy]

To test the correct air pressure of the expansion vessel within your boiler , you must first drain your system , until the pressure gauge reads zero . Then take a pressure reading of the air within the vessel .Should be within 0.8 to 1.5 bar , dependant upon the water content of your heating system .Check your manufacturers recommendations .

 

[Frazz]

Thanks for the info. Might have to call Halstead again as installation manual gives no indication of what pressure should be in the tank. Any ideas whether this does sound like a vessel problem though as it definitely is pressurized, but still venting through the PRV at less than its rating?

Cheers - Frazz