Automatic Air Vent

[HiQ]

Hello
I have a newly installed closed central heating system that has a difficult to find pressure loss problem.
The boiler is a Vaillant ecotec 612 which has an internal auto air vent - AAV.
I notice the installer has also included two further AAVs one the main supply and return pipes, about 4 metres from the boiler and before the motorised valves.
I am wondering if the extra AAV on the return pipe could have anything to do with the pressure loss problem?
BTW the pressure loss appears to be random and overnight when the system is not running.
Any ideas much appreciated.

 

[muggles]

The AAV could be causing pressure loss if it's venting air, maybe it's at a high point in the system and overnight air bubbles track along the pipe and are released?

 

[HiQ]

The AAV could be causing pressure loss if it's venting air, maybe it's at a high point in the system and overnight air bubbles track along the pipe and are released?

Yes, the AAV's are at a high point.
Could the system still be venting small amounts of residual air 2 months after first installed?
Many thanks.

 

[muggles]

Possibly, but unlikely, it's more likely that you have a leak somewhere. Did you have a sealed (pressurised) system prior to boiler installation or was it sealed during the installation?

 

[HiQ]

Possibly, but unlikely, it's more likely that you have a leak somewhere. Did you have a sealed (pressurised) system prior to boiler installation or was it sealed during the installation?

It was a vented system prior to the new boiler. I have searched and cannot find any evidence of a leak.
Many thanks.