programmer problems

[miffy190]

Hi, central heating programmer packed up, so replaced it with another sunvic the same, and that one packed up! Bought a simple siemens one , and that one broke! Seems that they both worked once, turned on the pump and boiler, then burnt out during the "switch off" cycle. I'm assuming now there must be a wiring fault somewhere- but on the switch off command? Any ideas? the lights are on on the unit, and the pump is running- but boiler not firing.
Boiler is an old potterton neataheat.
Thanks

 

[gas4you]

Is the FCU 3 amp fuse blowing when these faults occur?

Usually the most common things to blow things or fuses are anything with a motor in, eg the pump or the fan.

You need to be competent to test electrics with a multimeter before attempting to diagnose this fault, as you will have to test 240V AC live electrics.

 

[miffy190]

Hi, Dave, The fuse does not blow. The pump still works, and the lights and display are on on the programmer. Just changed the actuator on the two port valve (and another programmer)- this time I left the system on, but the programmer blew again on its own sometime later.
Mick

 

[simond]

What do you mean by 'blew'?

If you were vapourising your programmers you would have got through at least three by now.............

If you have two port valves there should be nothing connected to the HW off and CH off terminals. By the sound of it you have a neutral or an earth connected here.

I would check the fusing too while you're about it. Sounds like you do not have proper protection.