high pressure on alpha boiler

[davegirtch]

Recently the pressure in our boiler dropped to zero. I re pressurised the system and removed the fill loop. checking the pressure vessel it was also at zero. I pressurised this to 1 bar, which put the system pressure up to 2 bar. dropping the system pressure back down to 1.5 all seemed ok. Turning the boiler on caused system pressure to rise over 2.5 bar and the pressure relief cut in. system pressure wnet to 1.5 and then began to rise to 2.5 again. I turned the boiler off and the pressure dropped to zero. turning the boiler on and re pressurising the system goes through this same cycle of too high pressure then cooling down to zero. I have drained and refilled the boiler and bled all the rads but to no avail. Can anyone help please? is the pressure vessel faulty?

 

[Blake]

You need to isolate the boiler, drain it and then check the Exp Vessel pressure against the manufacturers specifications.

It may be perished inside so no longer regulating the natural pressure increase when the heating is on.

 

[bengasman]

That does sound like a defective expansion vessel.

 

[bobgarden]

Sounds like a nice cost of a new vessel too. If you can you could fit an external vessel from the boiler to do the job and at a lower cost of the boiler vessel.

 

[diamondgas]

Hi davegirtch,
Did you re-pressurise the vessel with the heating system open? If all you did was drop the pressure to zero then pumped the vessel to 1bar you may not have actually re-pressurised the exp vessel... Depending on the size of the vessel you can expect to pump a good few pints out of the exp vessel to pressurise it! ...

 

[davegirtch]

Ordered an external vessel at less than a quarter of the price of the Alpha one. Just minor alterations to pipework to do. Thanks for the tip!