New thermostat, old problem (wiring issue?)

[Karolisko]

On reflection, you may have to have the whole T4 unit assembled (with batteries). So remove it and connect two bits of wire to terminals A & B, reassemble it, turn up the heat setting to get the flame signal on and test for continuity (o) with the M.meter connected between the two wires, turn the setting down to check that the contacts open, M.meter reading 1.

This one is a bit unclear on reflection. There was a buzz when I tested for continuity on a plugged in unit so looking good here as well. But it's just backplate and wires I am testing. If I put a unit into back plate there's no way to test

 

[Johntheo5]

OK, will try again, when you want to install the stat you have to split it to enable it to be wired in? you then put it back together. so can you (or maybe this is what you are saying) connect any two bits of wire to A&B then with the unit all together+batteries move the setting up and down to get the relay to open/close with the M.meter on resistance, connected between these two bits of wire which will then tell you if the stat itself (forget about the wiring just now) is working correctly?

 

[Karolisko]

OK, will try again, when you want to install the stat you have to split it to enable it to be wired in? you then put it back together. so can you (or maybe this is what you are saying) connect any two bits of wire to A&B then with the unit all together+batteries move the setting up and down to get the relay to open/close with the M.meter on resistance, connected between these two bits of wire which will then tell you if the stat itself (forget about the wiring just now) is working correctly?

Yeah, that's impossible. In the old model the backplate and unit were one piece so I could have done the measuring just by removing the front plate. In the new thermostat front plate and thermostat are one, so after I connect thermostat to the back plate to fully assemble it I don't have an access to connectors or wires anymore.

 

[Johntheo5]

The plot thickness or maybe I'm thick, surely you can remove that new stat complete by disconnecting the wires and removing a few screws, I mean it was out of a box originally, and test it as suggested above??.
If you can access the A&B terminals (with mains wires (both) disconnected to test it then OK.

 

[Karolisko]

Ha ha.
If you are talking about testing disconnected unit I already done it (and attached photos) - see post #20.

 

[Johntheo5]

Well, if you probed the TOP TWO terminals (A&B) which I think you subsequently did and getting OC with relay clicking on/off the only conclusion is that you have a faulty stat, get a replacement and recheck.

For interest, probe between A&C this should switch as well but in the opposite sense.