we have a Baxi combi 800 boiler, 1.5 yrs old, and I have the heating flow temp set to 65 degrees. Today I just happened to be beside the boiler which had been sitting idle most of the afternoon due to unusual warm weather. I noticed that the water temp indicator displayed 26 degrees, and the thermostat just clicked on after a few seconds the flow temp started to rise, but when it got to 38 degrees it started to decrease down to approximately 18 degrees and then increase back to 38 before decreasing again. After about 5 cycles I turned on the hot water tap and the temp rose towards the set point of 60. When I turned off the tap, the flow temp decreased to approximately 36 before the boiler seem to kick in again and the flow temp started to increase towards the normal flow temp setting, and the radiators started to heat up. Can anyone offer an explanation, and if it occurs again I’ll get engineers out.

