Hi, I think my boiler thermostat is faulty (called out of calibration)? What happens is the heating takes ages to heat up now, the system is clean though the water is not sludged up at all. How can I check for the boiler thermostat being the cause. The hot water cylinder water seems OK though (maube it is less noticeable than the radiators) The boiler is old, Potterton: Flamingo II RS50. The pump is fine I have only had it fitted under a year ago, it is Grundofs 15-50. We have a 3 bed house. The probelm has been this way for about 4 days now.