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Message: <blockquote data-quote="Reptech" data-source="post: 559383" data-attributes="member: 38266">Good thinking on that, yes that could well be. I hadn't considered that.So the lunchtime test went off without incident. The fan cut off as it should although it was only a relatively short 'Comfort On' period. I've set it to come on again at 18:05 and to go off at 19:30 rather than 22:40 as it was originally before this trouble started. Lets see what happens with that one.Around 20:00 I'll manually turn the boost on for 2 hours (setting to fan only, no element) and see if it turns off on that setting.This might sound a bit 'out there' but these heaters make a slight twittery power supply noise all the time. Its very very faint but they do...I've noticed when I used the 'Advance' to cycle the comfort periods on and off at the end of the day when the fault appears for real I can hear the sound change slightly. It takes on a slightly buzzy character. Turn comfort on and that buzzy sound disappears but the fan runs the same through it all at what seems to be probably the slowest speed.So the command to turn off seems to be doing 'something' even though the fan carries on. Most of the switching on these for the elements and so on is done through solid state circuitry using Triacs but there is a single small relay on the board. I read somewhere that was for the boost element which is just the lower one of the three fitted.I have some pictures of the control board which I can post for interest.</blockquote>

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