I put in working order my Celtic RsC Boiler for heating a couple of weeks ago, and noticed now that no matter where the boiler thermostat is, temperature goes all the way up to 85 C with high flame when first switches on, then tries to keep to that temperature with low flame or no flame at all. But I remember the thermostat did regulate the heating temperature before, operating also on the flame depending on its position, but now seems to operate on the max. settings regardless of its position. Any ideas where could I look into? PCB maybe? Thanks