Danfoss cylinder thermostat problem

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To recap,
When my programmer is switched off at both the heating and hot water buttons the boiler will fire up on its own. The only way I can turn the boiler off is to turn the cylinder thermostat down to near zero.

What I have determined from this thread is that the dhw switch within the programmer is stuck on.
 
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Yes, that would seem to be correct.

Although in your original question -
The problem seems to be with the AT cylinder thermostat. When the temperature falls below the ambient setting the boiler will fire up even when it is switched off. I have to turn the thermostat down to near zero to knock the boiler off.
Which lead me to think that the tank stat did not function properly either.

It depends at what temperature it clicks.
 
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We're not all perfect.


If the tank stat only switches off at 'near zero' instead of the temperature of the water then it is not functioning correctly.
 
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If the tank stat only switches off at 'near zero' instead of the temperature of the water then it is not functioning correctly.
There could be a 'communications' problem here, in relation to the meaning of 'near zero'. Although there are some exceptions (albeit I don't recall ever having seen one that truly goes right down to 'zero'), they commonly only go down to 40 °C or 50 °C. That, coupled with the high degree of hysteresis one can get when adjusting such a stat, can mean that one often has to turn the stat virtually 'down as far as it goes' ("near zero"??) before it switches off.

Kind Regards, John
 
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I installed a new programmer last week and everything has been working as it should ever since.

So the problem was a faulty switch within the programmer.

Thanks to all who contributed to this thread.
 
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I installed a new programmer last week and everything has been working as it should ever since.
No, not quite everything.

I have used the earth wire for room stat to terminal 2.

I can't believe that nobody has said anything about that.

You must rewire using a cable with enough cores so that you do not need to use the G/Y one as a live conductor.
 

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