Possible fault with motorised valve

[JasperW]

I have had a minor problem with my central heating for a couple of years now and finally got around to trying to work out what is wrong this afternoon. The system works but the central heating only heats up if the hot water is also requesting heat from the boiler. This means that when it gets very cold the hot water does tend to run very hot. if the house is at the correct temperature then the system works as expected by cutting flow to the rads.

Anyway I had assumed it was something screwed with the rats nest of a junction box in the airing cupboard so I spend a couple of hours this afternoon tracing all the cables and checking the layout with a S-Plan wiring diagram. It all looks fine and I can see no errors in how it was set up.

I then put a voltmeter across the output of the motorised valves

Both valves on: 245v
H/W valve only: 245v
C/H valve only: 153v

I am assuming this is the cause of my problem; the 153v level is not being recognised by the boilder as a call for heat and is not switching on. A couple of years ago I changed the H/W valve but the C/H valve is the original from when we moved in 2004 (the boiler was changed to a Worcester Bosch in 2006).

I am assuming that changing the valve motor and electronics should fix this problem. I seem to remeber that if the valve is working all I need to change is the motor.

https://www.screwfix.com/p/honeywel...-replacement-powerhead-22mm-compression/326fv

I was really just wondering if anyone with more experience of these things can spot any flaws in my fault finding or has any suggestions / advice. The only thing that bothers me a bit is the 153v, could something else be pulling the voltage down but then I don't know how the switching is done within the controller.

Thanks

 

[ianmcd]

your CH zone valve actuator is faulty

 

[Alec_t]

Could be just the microswitch inside the actuator which needs replacing.

 

[JasperW]

I realised that after I posted this I might actually be able to pick up a replacement valve actuator from ScrewFix which is a two minute walk from me. Amazingly they were still open and had 8 in stock. swapping it over was a very easy and now I can have room heating without needing to have the hot water heating at the same time. I guess it was the micro switch that was on the way out.

 

[ianmcd]

you are welcome

 

[JasperW]

After 24 hours the central heating is continuing to work normally so I guess it was the actuator that was at fault.

Thanks Ian and Alec for the confirmation of my diagnosis.