Pressure problem with alpha cb25

[Gary80gas]

From cold boiler pressure shoots up in seconds and dumps through prv whether hot water or heating. If you persevere with heating and get it running even on very low heat all settles down and boiler works fine, heating and hot water. Let system go cold and run hot water and system dumps again. I don't understand why it all runs ok with as little as 20deg of heating or higher. Puzzling. Any advice appreciated.

 

[Chalked]

What’s the ex vessel charge?

 

[Gary80gas]

The vessel is charged to 1 bar

 

[Gasmk1]

is the feed tube to the ex vessell blocked had this on a boiler once

 

[Gary80gas]

Im not sure if its blocked or not. Once the heating is running even at the lowest possible temp for a few minutes it all operates ok. Let it go cold and call for heat and the pressure flies up and discharges.

 

[Gary80gas]

I got invited back again and solved it. I took the plug out the pump front and this time the pump would spin and stop, spin and stop. I checked power was continuous and so changed PUMP. I can only guess that the pump was warming up before and this is why it always worked once it was running. Also I should mention our favourite friends with penguins, it was under contract, had said they were not touching it because it definitely needed a power flush and extra air vents above boiler cutting in, all for bargain price of nearly £1400. Needless to say the water was clean and all it needed was a pump head change. Second occasion this year Ive found them making a serious misdiagnosis and profitable work for themselves. Not good enough.