Danfoss cylinder thermostat problem

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OK. I stuck a mains tester screwdriver in terminal 10 with the programmer switched off and the atc cylinder stat at zero. I am getting power.

So I switched wires 4 and 8 on the junction box and physically switched heads on the motorised valves to check if the hot water valve was sticking.

This did not change anything. The hot water still fires up when the programmer is off and the thermostat is below ambient temperature.

The heating is working fine too. Terminal 10 is still reading live.

This would appear to discount the sticking valve theory.

Faulty programmer?????
 
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OK. I stuck a mains tester screwdriver in terminal 10 with the programmer switched off and the atc cylinder stat at zero. I am getting power.
A mains test screwdriver is not reliable enough.
Terminal 10 should be at 240V to earth when the programmer is calling HW ON.
The boiler still should not run with the tank stat open.

So I switched wires 4 and 8 on the junction box and physically switched heads on the motorised valves to check if the hot water valve was sticking.
Good idea.

This did not change anything. The hot water still fires up when the programmer is off and the thermostat is below ambient temperature.
Right.

The heating is working fine too. Terminal 10 is still reading live.
Ok but even if the programmer was not switching off HW ON it should still be controlled by the tank stat.

This would appear to discount the sticking valve theory.
It would.

Faulty programmer?????
If T10 is always (properly) live then yes but the tank stat must be stuck on as well.

Bearing in mind the neon screwdriver may light spuriously -
Are terminals 8, 14 and 15 also permanently live?

You really need a reliable voltage detector.
 
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A neon screwdriver isn't really a reliable tool for proving live (and especially not for dead) but if terminal 10 is live with the programmer switched off then it definitely suggests the programmer is at fault.

Can you post a photo of the programmer wiring diagram just to confirm it's not a wiring error there? It should be shown on the back of the programmer.

Also, does terminal 10 go dead if you physically remove the programmer from its back plate?
 
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I stuck the screwdriver in as requested.

8 dead, 14 dead, 15 live.

I removed the programmer from the back plate and 10 and 15 are now both dead. (I did remember to turn the power back on at the spur after removing the programmer from the face plate)

Faulty programmer looks more certain now???
 
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It looks like you do need a new programmer but If 8 and 14 are dead then the tank stat would appear to be working properly.

However, something else must be wrong.
If 8 is dead the HW valve will/should not operate to turn on the boiler and pump.
 
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When I got the dead readings at 8 and 14 the cylinder thermostat was turned down to zero.

I just turned the thermostat up until I heard an audible click in the thermostat.

Checked 8 and 14 again. Both were live. (and the boiler fired up)
 
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Before digging too deeply into the external wiring go back to the boiler and check the wiring connections in there.

Many new boilers have a link (links) between the main live and switched live terminals so the boiler will run out of the box. This link (links) needs removing as they effectively over-rides some, or all, of the external controls depending upon boiler configuration.
 

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