Hot water off – intermittent fault

[skatesy]

I have an Alpha conventional boiler with Y Plan. Up to recently, both CH and HW worked fine but the HW would go off occasionally. Switching the main supply off and on seemed to fix that for a while.

But now the HW seems to have packed up completely. I have checked the wiring and have done as many checks as I can. Both room and cylinder thermostats seem OK. I have checked the power to terminals under different condition and there always seemed to be an anomaly that did not match the circuit diagrams. After much checking, I found that, T6 (from HW-on, going to C on cyl stat) and T7 (from HW-off, going to 2 on cyl stat and grey to motorised valve) were both powered. Perhaps T7 (HW-off) is cancelling T6 (HW-on)?

I disconnected the lead from HW-off to T 7. The motorised valve went to the mid position (A+B) but the boiler did not fire. I reconnected the lead, CH came on the valve motored to the B position, CH came on but no HW.

With heating and water calling I get power on Terminals 4,5,6,7 and 8. All this seems to indicate that the programmer is at fault and sending out both HW off and on signals but I would like to confirm this before paying £90 for an Alpha programmer.

Initially I thought that the motorised valve or motor were faulty but they seem to be moving OK and I would rather not waste £100 on replacing them without curing the problem plus the bother of draining the system.

Any help or advice gratefully received

 

[diamondgas]

Where's the valve when calling for hot water only? What make 'y'plan valve do you have installed?

 

[skatesy]

Where's the valve when calling for hot water only? What make 'y'plan valve do you have installed?

Honeywell Y Plan.
I wound down the room stat and checked that the cylinder stat was calling. Valve was in position A. However, I then switched off the main supply, the valve went to position B but the bouiler did not fire.
I then wound up the room stat so it was calling for heat, valve went to positionA, the boiler fired, Terminals 4,5,6,7 and 8 became live.

There must be an explanation but I can't think of it!!

 

[diamondgas]

Position B is hot water only, A is heating only, AB shared! No idea what you're on about regards terminals to be honest, however for the valve to move to 'A' requires a live to the white (r/stat) and grey (h/w satisfied).... Sounds like you have some dodgy wiring or a diverter actuator fault IMO