Worcester boiler 24 CDI, boiler does not fire when there is demand for DHW otherwise it fires up

25 Nov 2005
Reaction score
United Kingdom
This boiler dose not fire up when there is a demand for DHW, but the it fires up when there is a demand for CH. The diverter valve works ok its head extends when there is a demand for DHW and engages with the microswitch on top of it. Also the pump is working but the boiler does not fire. I also tried to the run CH and open the hot tap and as soon as I do that the boiler stop firing. Any idea please
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I did more test on the boiler today and found out that both the fan and the pump work for a short time then they stop when there is a demand for DHW. this gave me the indication that the microswitch is working and does its job by passing the order to the PCB to fire the boiler However, when they stop, I could hear clicking noise inside the boiler as it wants to fire but it could not. this led to to think of the DHW sensor and as soon as I replaced it with one I took off Hallstead boiler, it started working as it should. happy days
You do realise that thermistor temperature/resistance profiles can vary considerably and you may have compromised the safety.
good point, however, I believe most combi boilers work on the same principle when it comes the DHW output. also it is sensor responsibility to to shut the boiler down when the temperature accedes the limit. furthermore, both sensors looks exactly the same , identical
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You believe wrong...there can be a vast difference in thermistor profiles...at 20 degrees some might be only 10s of ohms others 100,000s of ohms.
Fit the correct part.

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