My heating system comprises new(ish) boiler (Potterton Suprima 100), hot water cylinder (with cylinder jacket), 2 port motorised valve, pump and control unit (Lifestyle LP522).

There is currently no cylinder thermostat and adding the wiring for one would be a pain.

Is it reasonable to fit a cylinder thermostat and have it prevent the CH pump from operating if Hot Water only selected AND water in cylinder is at the desired temperature?
I realise that the cylinder thermostat SHOULD be wired back to the controller to prevent the boiler from operating in this case.
My questions are
1) can I isolate the pump instead of the boiler for HW only? (the pump is next to the cylinder)
2) If I can - is it sensible and HOW can I do it?
3) Will it be inefficent (how wastefull in money terms)?
4) Will it damage the boiler - I presume that it would only fire up if the water temperature dropped significantly, which it shouldn't do if its not circulating.

Stephen Clark, March 2008

T,

I have just had the motorised valve replaced and it now works correctly. It shuts off the flow to the rads when HW only is selected which is what I want. Heating operation is fine, my concern (over the summer particularly) is for HW only operation.

As there is currently no cylinder thermostat, the pump is running all the time that the HW is selected on the timer, even when the water in the cylinder is up to temperature. The boiler then only fires up if it detects a drop in temp of the circulating water.

In an ideal system, I would fit a cylinder thermostat and wire it back to the control pannel so that it can electrically switch off the boiler until it detects a drop in temp. This is clearly the most efficient solution. It is this connection that would be a pain (I don't want to re-decorate just yet!).

My question is can I switch off the pump if the thermostat is recording the appropriate water temperature. And will that safely prevent the boiler firing up?

Stephen Clark, March 2008

Is your motorized vavle not allowing you to select between HW and CH? or is it there to zone the house?

T, March 2008

Water MUST circulate through your boiler. end of.

T, March 2008