My heating only comes on when my cylinder calls for heat then shuts off when
cylinder gets to temp. There is a 2 port valve on the heating that opens and
closes with the room stat. I've tried a different programmer so its not
It sounds like you may have a S plan system.
Have a look at http://content.honeywell.com/uk/homes/systems.htm
to be sure.
If it is an S Plan then the micro switch in the heating 2 port valve has
failed (or you are lucky then its may be a loose connection in the wiring
You may be able to change the microswitch or just the head on the 2 port
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