From one of the valves the pipework will lead to the HW cylinder. The heating will only come on because the CH valve is stuck. The valve can not fully open and depress the actuator that would trigger the boiler to fire up. When the HW is turned on the boiler fires up because the valves works...
Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.