I have a Ravenheat RSF82ET, I recently had a problem with the domestic hot water which I resolved by replacing the diaphragm and microswitch on the diverter valve. The hot water is working perfectly but I now seem to have trouble with the central heating. The boiler fires up and runs OK till the central heating gets up to temperature/pressure and then turns off. When it fires back up again it only runs for about a minute and then turns off again. Also I have noticed that there is water coming out of the auto air vent valve. Do you think I may trapped air in the system?