Boiler not lighting when divert valve in 'Mid' position

[Ukdodger]

Hi, I changed this divert valve like for like.

ACL Drayton (Invensys) MA1/679-3 Mid-Position Motorised Valve

When only heating is required the valve moves to 'H' as it should and the boiler lights.

When only hot water is required the valve moves to 'W' as it should and the boiler lights.

But when both water and heating are required the valve moves to 'M' as it should but the boiler doesnt light.

I've checked and double checked the wiring from the valve to the junction box. They are correct. When I changed valves I changed each wire one for one. So I took orange out from the old divert valve connector and replaced it with the orange from the new valve and so on for each of the four wires. I dont think the problem is with the wiring. Any help greatly appreciated. Thanks

 

[stevetheplumber]

faulty valve?

 

[Ukdodger]

Unlikely I thought as it's new and isnt it the Controller that turns the boiler on/off not the valve?

 

[REDSAW]

does the pump run in 'm'?

 

[Ukdodger]

Yes it does.

 

[REDSAW]

give the valve a whack, had one just before xmas. hit on the side made it work again?

 

[Ukdodger]

give the valve a whack, had one just before xmas. hit on the side made it work again?

Thanks Redsaw. I'll give it a try. But is there a diagram anywhere that details the circuitry between the Controller, Valve, heating and water thermostats. For the pump to operate it must get a signal from either or both thermostats and the Valve. If I knew which wires were which I could check for a voltage?

 

[stevetheplumber]

just search for honeywell y plan wiring diagram like this Wiring Diagrams - Honeywell UK Heating Controls

 

[Ukdodger]

Excellent Steve just what I want. Thanks.