Honeywell ST9100C programmer/thermostat wiring problems

[stem]

I have linked terminals 1 and 4 of the programmer backplate but still the central heating fails to operate.

If the boiler works with the link wire between boiler terminals 3 & 4 and doesn't work with a link between the programmer terminals 1 & 4, then I suspect that there is a wiring fault between the boiler and the programmer, because electrically speaking, both will achieve exactly the same thing.

I'm not a lover of volt-sticks, but could you try seeing is there is voltage (they sense voltage not current) on terminal 3 and 4 of the boiler with the link removed. I would expect 3 to be live and 4 not to be live.

 

[Kingbroady]

Thanks. Yes, 3 is live and 4 is not.

 

[stem]

OK good, How far is the boiler from the programmer?

 

[Kingbroady]

Several metres. The boiler is upstairs with the programmer in the downstairs hallway.

 

[stem]

It could be the thermostat, with everything back as per my diagram, try linking the grey and brown wires in thermostat terminals 1 & 3. You can do this by putting them both in terminal 1.

Sorry, I edited what I had previously written here I forgot about the existence of the room thermostat, which is looking more like the possible culprit. I assume that the thermostat is high enough to be calling for heat when you were trying it earlier.

 

[Kingbroady]

Thanks. I linked the thermostat wires as you described and the central heating now works via the programmer. Therefore, it appears to be a faulty thermostat. I'll order one and let you know how I get on with that.

Thanks again for all your help.

 

[stem]

Well done! You got there in the end. It's unusual for a Honeywell thermostat to fail they are usually pretty robust. At least you will have time control now.

 

[Kingbroady]

Swapped over the thermostat and that's done the trick. Thank you for all your help. It really reaffirms your confidence in the kindness and generosity of human nature on occasions such as these. Thanks again.