System pressure fluctuates between 1 bar (cold) and 1.8 bar (hot)

[philbury]

I have recently had three episodes of my 8 month old Vaillant installed Ecotec832+ losing pressure overnight and being below operating pressure (.3 bar) form a normal pressure the day before. Vaillant have been out to check but find do fault with the expansion vessel or the PRV. There are no apparent leaks in the system which is 13 years old and mostly plastic pipe. The system ran without the need for any secondary expansion vessel the last 13 years with a Glow worm Cxi80. Is it normal for the pressure to go up and down .8 of a bar between hot and cold? Any ideas what's happening?

 

[Scott_D]

Could be a leak that only shows when hot
Best to pay the installer for a few hours to come back and run some tests

 

[philbury]

I'm definitely calling Vaillant out again, I've just been trying to gather info here to counter their previous diagnosis that there was no problem with the boiler or their installation.

 

[Scott_D]

Top up the pressure to 2.5 bar
Turn off boiler
Shut the flow and return valves under boiler
Leave for 24hrs
See if the boiler has lost pressure
Open flow and return valves and see if the system lost pressure

 

[philbury]

Thanks - useful tip.

 

[ShaunCorbs]

In that time don't use the boiler eg heating or hot water

 

[philbury]

I could surprise the family on Christmas Day