Low pressure on combi boiler

[mg_graham]

I find that the pressure constantly drops below 0.5 when the central heating is switched off.

I have to always open the valve to increase the pressure. When CH comes on the pressure rises as normal. When CH switches off it drops down to 0.

I have tried bleeding the radiators but they seem fine.

Any ideas.

Thanks

 

[Bahco]

You are losing water somewhere.
Check all joints etc. If no leaks evident suspect your PRV is leaking

 

[mg_graham]

Thanks - don't seem to be laking internally so will check outside - what is a PRV though

Thanks

 

[IanDB]

Pressure Relief Valve. This lifts at 3 bar.

When CH comes on the pressure rises as normal.

The pressure should stay fairly constant at around 1 bar (if that's what it's set to). If you are saying that the pressure is increasing as the boiler warms up it could be that your expansion tank needs recharging/replacing. If the pressure is building to 3 bar the hot water will be vented off through the PRV. When everything cools down the pressure will drop back - as some water has been released from the system it could go to 0.

 

[Bahco]

Pressure Relief Valve is what lets the water out of the boiler either manually or automatically.
It is attached to the pipe going outside. Check there is no water leaking out.
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