I came home after new year to find the central heating not working. I traced it to the microswitch in the CH zone valve (Honeywell V4043H) failing to close when the valve opens. I've ordered a new powerhead for the zone valve and while waiting for it to arrive I'm wondering if there's anything I should know about fitting it. It looks like just two screws to remove it and replace it. Is there any more to it than that?
In the meantime I've rigged up an override switch to the pump, bypassing the controller and room stat. When I want heat I open the valve manually and flick the switch. I'm very careful not to switch the pump on unless the valve is open, but I wonder what would happen if the pump was switched on with both zone valves (CH and HW, both less than a foot from the pump) closed? Would there be damage?