My boiler is very reluctant to switch from DHW to CH. When both DHW and CH are in operation when I run the hot water the green indicator remains lit and the boiler will not return to supply the CH demand - only if I run the hot water tap once again to the point that the boiler fires up to meet the demand will the green indicator light begin to flash - once the tap is turned off, a little while later the CH will then operate - during the switch over I notice a ticking sound towards the left site of the boiler which then stops and the CH operates. I suspect the diaphram in the 3 way valve assembly - any ideas ??
If the diaphram is the cause would I need to drain the boiler to carry out the replacement ?? - I replaced the DHW diaphram approx 6 month ago.
Tnks