I have changed the air vent as it was leaking water and akso the pressure relief valve.
But if I set the pressure at 1bar when hot it goes to 3/3.5 and pushes water out of relief valve.
if I set the pressure low it is OK, but over a period of time the pressure kreeps up(over the summer it was set to just above zero now it is at just over 1bar.

stephen, September 2010

i think as the first answer try the loop if it make no different then its the dhw. your water pressure must be around 2 bars mains when it heats up it expands to 3 bar then when you cool it from 2 bars it drops to above zero then this causes the mains water to seep through slowly again increasing the pressure to within mains pressure slowly

kash, September 2010

when the central heating is on the pressure goes 3bar and it vents.
But if I bleed some out of the ragator and drop it to 2bar it stays ther until switched off, when it drops to just above 0bar.
And as I said if then left withno heating on the pressure gradualy increases to about 1bar.
I have suspected the filler loop tapbut what do you think?

stephen, September 2010

its most likely a hole in the dhw heat exchanger where the water from the cold supply is creeping into the central heating system. its the same as as leaving the filling loop open as this does the same first disconnect the filling loop pipe see if its seeping through there if not then its the above. new heat ex required

kash, September 2010