Grant Combi Max - pressure loss problem

[petes7457]

Hi,

Changed the fill loop and associated leaky valves on the above boiler. Drained boiler and refilled. Checked expansion vessel pressure at 1 bar when system full but at zero pressure. Re-pressurized to 0.75 bar and checked. System run in CH mode for 1 hour and worked fine. HW fine also.

Switched boiler off today to see what cold system pressure went to and found it had dropped to zero after a few hours. No apparent leak through over-pressure or air-vent valves. Re-pressurized and everything okay again.

I'm a little stumped as to what is happening here. Pressure when hot is around 1.5 bar - not sure what this should be.

Please advise, Pete

 

[adlplumbing]

check the pipe at that goes outside and see if it wet

 

[petes7457]

No, not that I can see.