CH only works when HW is on

[jgrigor]

Last week my central heating went off when it was set to be on, I
managed to restart it by powering off/on the controller/boiler.
Since last night the central heating only works when the hot water
program is active. As soon as the HW program goes off then the
central heating doesn't work, no boiler activity, pump is off.
The controller is a Siemens RWB29 but I tried the old LandisGYR
controller but the problem is still there.

The boiler is a Glowworm Ultimate, any ideas what the problem might be?

 

[Agile]

You have not given us much information on your system!

Its probably a faulty motor valve in the heating circuit.

Tony

 

[jgrigor]

Sorry for the lack of detail
Boiler is Glowworm Ultimate, system is open-vented fully-pumped,
Y plan (I think).
5 rads downstairs, 4 upstairs. Everything installed in 1997.
HW Cylinder, Pump etc in upstairs cupboard. Boiler is in kitchen.

James

 

[corgiman]

as tony says you need to change the syncron motor in the three port valve

is it a honeywell? if it is its a POP to change

 

[Agile]

I dont think its the motor as otherwise there would never be any heating.

It seems as if the microswitch has failed or the actuator is stiff or jammed and does not allow the motor to drive the valve far enough to reach the microswitch. Or the mechanism is just worn and not operating the microswitch.

Tony