Slow pressure drop on worcester bosch boiler

[TryAgain1]

Have a Worcester Bosch oil combi boiler with a slow pressure drop (drops from 1.5 bar to 1 bar over 2 months). Boiler feeds about 12 rads. Property is a bungalow. Have checked multiple times for leaks can't see any either by rads or under floor. Pipework is clipped to joist no screed or concrete/cement embedded pipes (all pipework). Zero sign of pipe leaks . I top up with inhibitor and leak sealer regularly. Only thing I can think of is insufficient inhibitor (fernox).

 

[Mister Banks]

Have you checked for a dribble from the PRV?

 

[TryAgain1]

Have you checked for a dribble from the PRV?

The PRV inside the boiler?

 

[Mister Banks]

The PRV inside the boiler?

Check the pipe that goes to the outside.

 

[steven lee]

At that slow a rate of loss it's almost always a weep that's evaporating before it ever shows, so I'm not surprised you've found nothing visible. The quickest way to narrow it down is to isolate the boiler from the system overnight - if the boiler side holds pressure and the system side drops, the leak is in the pipework and you can work round the rad valves and joints one zone at a time. Also worth checking the expansion vessel charge, as a flat one will push a little water out of the PRV every cycle and it looks exactly like a mystery leak.