Variable hot water, heating works fine.

[booke23]

I have an old Ideal Classic NF50 boiler on an open vent system with a hot water tank.

The radiators are always very hot but the hot water seems a bit variable. A lot of the time, no matter how long I run the boiler to heat the water, the water in the tank only gets warm....perhaps 50C. Then sometimes the water gets up to high temperature.....75C.

There is a tank thermostat, but that is turned up high, and as far as I can tell the boiler fires continuously when hot water is selected on the controller.

I suspect the 3 port motorised valve is sticking, but are there any other possibilities worth considering?

 

[booke23]

Been investigating this further today. The tank thermostat gets hot when the system is running....even though the water in the tank is cold. I now suspect this is at fault and may be cutting the boiler when as it gets hot.

Slightly worrying that it should get hot all by itself!