Back boiler .heating wont switch off

[spanners1967]

hi... went to look at a job where was told that the heating did not switch off during the night as it was programmed to do. the system has a 2-port valve on the heating side and no controls for a room stat. it's a baxi bermuda back boiler and a five year old programmer.. i was thinking it was the programmer at first but now suspect the zone valve... how do i prove which one it is??? any advice gratefully received

 

[diamondgas]

Hi spanners 1967 .... The way I check is to remove the programmer from its back plate and turn the fuse spur back on. If the boiler fires up I'd suspect the valve! How is the hot water controlled?

 

[aggis]

The zone valve has a permanent live to the micro switch, if the m/s is jammed on, it'll put a live thro' to boiler. Turn off power at fuse spur, open junction box that connects the zone valve, there should be no continuety on orange & grey if working correctly.
If there's continuety the valve req's changing.