Hot water prob. Anyone explain this please?

7 Jun 2009
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United Kingdom
My system - Halstead Best db40, fully pumped, CH - Zone valve & room stat,HW - Zone Valve & cyl stat, Siemens RWB9 Programmer. Problem - recently I started to hear a clicking or arcing noise from around the on/off switch area within the boiler when the programmer created a demand for hot water but which stopped after a few seconds and the boiler fired,pump started etc. But when I came back of my hols my son told me that the boiler would not give any hot water at all - CH seemed fine. On investigation I discovered that whether I pressed HW or CH on the programmer I got 240v at Terminal 1 on the boiler (coming from the switched live lead in the main wiring box) but choosing HW would NOT fire the boiler up or start the pump and there was no clicking noise.If I chose both HW & CH then all was ok. I contacted Halstead and they said if the boiler was working on CH then it was probably ok but to check all wiring of external controls and maybe the HW Zone valve. I did this and all seemed ok - I took the HW zone valve actuator head off and watched it turn and give 240v out from its endswitch , the valve itself was free with no sticking.I replaced the actuator head with a new one and the problem dissapeared. Fine- but what I dont understand is if I was getting 240v from the HW Zone valve to the boiler what was causing the problem that the new actuator fixed?Thanks in advance.
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A bad connection that you unknowingly fixed when the new head was fitted?

Could explain the 'arcing' noise.
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Yep - 240v at Terminal 1 on boiler chocolate block (switched live lead) which in turn comes from the orange lead from the HW Zone Valve.

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