My parents boiler has started to play up, the heating side works great. The problem is with the hot water. When I turn the taps on, the boiler lights up for a few seconds and the water runs hot for a very short period, then starts to run cold. After about 20 seconds the boiler fires up again warms the water for a short time then turns off again :? . The cycle continues. After downloading the fault sheet from Ravenheat I tested the 10k resister switch and this checks out ok, the only other thing I tested was the thermocouple. With the water cold it read about 14k ohms. Does anyone know if this sounds like the problem? Does anyone have the engineers test sheets. Any help would be appriciated, or if this is all wrong can you steer me in the right direction.
The thermocouple is to sense the pilot flame - nothing else.
It's the DHW sensor you need to be checking, maybe a scale build up or just the age of the sensor. A sensor with a build up of limescale on it, will retain the heat longer than a new one, therefore telling the boiler the hot water is at the correct temperature.
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