Failed central heating valve?

[Roger Mills]

There's something wrong with that wiring!

The functions of the actuator wires are as follows: Brown - Live to the motor. Should be live when the programmer/room stat are calling for heat Blue - Neutral to the motor Grey - Permanent live to the micro-switch Orange - Switched live. Provides feed to boiler/pump when the valve is fully open

The 4 wires from the programmer to the actuator need to fulfill the same functions. I cannot say which is which because it depends on how they are connected at the other end.

The fact that manually operating the micro-switch makes the boiler fire suggests that the two wires connected to that (brown/grey and black/orange) are ok. On that basis, the blue wire should be connected to Neutral in the programmer and the other black wire should be live when the programmer/stat are calling for heat. My hunch is that there's discontinuity in one or other of those wires.

[binnsroad]

Apologies for the two year delay! Very briefly, for the last two winters I have just used the little switch on the side of the valve to turn on heati ng for that zone, which is fine as long as another zone is already calling for heat.

Taking Roger's point, I checked the cable coming from the controller today, and yes, of the four wires, one is dead whether or not the controller is o n or off. Removed the controller from the wall then had a (very late) brai nwave. Four zones, all with identical controllers, so swapped a known work ing controller, and all works perfectly, so it is the control box (programm er) which is not working. Tried cleaning the contacts, no change.

Why didn't I think of that, two years ago?

The programmer (Drayton LP711) has changed in appearance since ours was fit ted 14 years ago, although the connections look the same. Is it likely a m ore modern version of the same model number will be a simple plug in replac ement?