boiler losing pressure?

Turn off all the rads up stairs and monitor the pressure.

If that does not help do the same on the down stairs rads

If it stops the leak, it may be a rad , TRV or lock shield check it with small pieces of tissue tied around the end valves on all your rads.

The system you describe has confused me, do you have only one or two pressure gauges within the circuit.... You say you put 12 psi in the expansion tank Why 12 PSI???

!4.7LBS = ONE BAR Most systems run on a minimum of 1 to 1.5 Bar that = 14.7 > 22.5 LBS if you where to take it up to the correct pressure you might find the problem much faster..

If I have missed something in your question ...Sorry but I think not !

Pat
December 2008

Theres got to be a leak somewhere! It may be small and slow but it will be there. Sods law says it will be under the floor boards and hard to find. Can you get under the floor to look? Also check your ground floor ceilings carefully for any sign of a damp patch from above. I had a boiler losing pressure for months, gradually got worse and worse - eventually found a fifteen year old soldered joint had given up and was dripping away slowly behind a false wall. Walking in bare feet I felt the damp on the carpet that was how I found it!

Richard
December 2008