Expansion vessel

[Julian]

Hi
I have a 6 year old Potterton puma 100 that keeps depresurising when it cools down, I fill to one bar switch on and as the boiler heats up the pressure rises to 3 bar, pressure relief blows etc. If I leave the boiler running I can keep it running for days at about 2 bar. If I switch off pressure drops top zero. My first thought was a leak but now thanks to the forum I recon the expansion vessel has gone. How can I check and should I replace with same or fit external vessel? If so any recomendations

 

[oilman]

Search the forum for "expansion vessel" or "PRV" or "filling loop". There's loads of recent posts. Try looking at my posts as well.

 

[Julian]

Hi
I thought you might like to know that the problem is now sorted and I will give a brief desciption of the fault in case anyone else ever experiences something similar. I checked the air pressure in the vessel and it was 0.2 bar, handbook says 1 bar so I thought this may be the solution, pumped up to 1 bar same problem as the water heated up it expanded and went out of the PRV.
I then thought why is the expansion vesssel not doing its job so I checked the flexible hose joining it to the boiler pipework ..... it was jammed solid with black oxide, cleaned it out and all is now well .... and yes there is corrosion inhibitor in the system, I think I will flush it out and re-dose it

 

[oilman]

Make sure you check the expansion vessel air pressure with zero water pressure. 0.5 bar will do if you have a two storey house. This reduces the stresses on the expansion vessel. Then set the water pressure to 0.2 bar above the air pressure when the system is cold.

 

[Julian]

Hi

Yep, set the pressure with the system empty, so far so good, the system has been up to full temperature, back to cold and back to temperature and the pressure seem Ok

Very useful forum !!