I think I've managed to solve the issue of CH not functioning outside of the HW time periods when using weather compensation by using the changeover contacts of the HW timer.
The modified wiring is
here if anyone could give it a once over?
Conventional setup operates as follows:
1. HW demand (time + temp) = Valve sprung to HW, boiler runs at full output (not weather compensated)
2. CH demand (time + temp) and HW demand (time + temp) = HW gets priority (valve sprung to HW), boiler runs at full output (not weather compensated)
3. CH demand (time + temp) and no timed HW demand (but cylinder stat satisfied) = CH gets flow (valve activated to CH through satisfied cylinder stat), boiler runs in weather compensated mode
4. CH demand (time + temp) and no timed HW demand (and cylinder stat not satisfied) = HW gets flow (valve spring to HW) but boiler runs in weather compensation mode and may never satisfy cylinder stat hence CH won't ever get to function [This is the problem scenario]
The revised setup operates as follows:
1. HW demand (time + temp) = Valve sprung to HW, boiler runs at full output (not weather compensated)
2. CH demand (time + temp) and HW demand (time + temp) = HW gets priority (valve sprung to HW), boiler runs at full output (not weather compensated)
3. CH demand (time + temp) and no timed HW demand (but cylinder stat satisfied) = CH gets flow (valve activated to CH), boiler runs in weather compensated mode
4. CH demand (time + temp) and no timed HW demand (and cylinder stat not satisfied) = CH gets flow (valve activated to CH), boiler runs in weather compensated mode
The key benefit is proper function of scenario 4 i.e. even if the cylinder stat is not satisfied outside of timed HW demand then the CH can still function, even in weather compensated mode. An additional benefit is that the valve does not remain energised when there is no CH demand and the HW temperature demand has been satisfied (but is still within the HW time period).
Mathew