Zone valve fails to close when OFF if other valve is open

[kevnurse]

The subject title says it all, but to simplify:

If the dual controller switches either the CH or DHW on, while the other system is off, the the associated zone valve opens and, stats permitting, the boiler then fires up and the pump runs. The required system then operates as normal. When the controller switches the operating system off, the system shuts down and the associated zone valve closes. I know the zone valve operates as required because I can see the indicator pin moving from A (close) to B (open). No problem there.

However, if both systems are on and both CH and DHW zone valves are open and the controller switches off either system, the associated light on the controller goes out but the zone valve remains open (the pin does not move). Given that the other system is still on at this time, this means that both systems will continue to receive boiler and pump output although the controller indicates that only one system is on. The rads remain hot and the DHW remains hot until the controller switches off the remaining desired "operating" system and then both zone valves close and both systems cool down.

Thoughts anyone?

 

[D_Hailsham]

Wiring fault.

Check that the grey valve wires go to a permanent live (usually terminal 1 in the junction box) and the orange wires go to boiler live or switched live (depends on boiler).