Okay i'll see if i can contact someone who's more familiar with this unit, generally its the diaphram which goes first as its in up and down mode all the time. followed by sensor in chimney, they are a reliable model and NOT known for o-ring failure...as are some models...
There is a small leak from a pilot hole just below where the tiny copper tube from the pressure gauge enters the boiler.....the boiler is about 10 years old and fuctions really well apart from this...any ideas how to cure this...
thanks Jim tylee