Mid position valve faulty?

[mickey dee]

Afternoon all

I would really appreciate some help on this if possible. I Recently fitted Honeywell timed Y plan pack- ST9400 programmer and V4073A mid position valve, HW and CH work independently, the problem is when they are both on together, when the HW is satisfied it also knocks the CH off as well even though it is still calling for heat, I have tried turning room stat off and back on again but cant get the boiler to fire, I have to do a mains reset to de-energise the valve and start by switching CH on again which fires the boiler.I have checked all wiring which is correct and also done some voltage testing on the white,grey and orange wires from the valve:

HW and CH off 0v white 240v grey 0v orange
CH on 240v white 240v grey 240v orange
HW and CH on 240v white 148v grey 240v orange
HW satisfied CH still calling (boiler not firing) 240v white 240v grey 0v orange

Am I right in thinking that the orange wire should be energised to switch the live for the boiler to fire and if so would it be switch that is at fault within the powerhead?

 

[Bolty123]

Have you fitted a brand new complete valve or just the head. Sounds like it's getting stuck which is common on old valves not on new ones though

 

[mickey dee]

Have you fitted a brand new complete valve or just the head. Sounds like it's getting stuck which is common on old valves not on new ones though

Yes, fitted brand new valve that came in the pack along with both stats and programmer

 

[AWheating]

could well be the valve. you have voltage on white and grey which indicate the controls are calling for central heating only.

 

[mickey dee]

could well be the valve. you have voltage on white and grey which indicate the controls are calling for central heating only.

I just wondered where the live would come from to ignite the boiler as there is no 240v on orange wire, just looking at Y plan diagram, that's what got me thinking it was the switch rather than the valve

 

[neily01]

Faulty prog by the sounds of it, have had loads.
which ever channel calls first works, the other channels light comes on but the tell tale click off the relay switching dosent happen. Can turn the second on and off as much as you like relay wont click until first channel turned off. Always the st9400's and usually that fault but have see other faults.

 

[mickey dee]

Thanks neily02 thats just got me thinking cause it has been intermittent, a couple of times I did notice if I put CH on first then HW then switch the HW off the CH does stay on but very rarely it happens so you could have a point, I should be covered under warranty as it only 6 month old

 

[Bolty123]

With the voltages you have the orange should have 240 on it when the valve motors over to ch only it should make a switch to get your voltage on the orange.

 

[mickey dee]

With the voltages you have the orange should have 240 on it when the valve motors over to ch only it should make a switch to get your voltage on the orange.

Thanks Bolty got it wrong way the valve moves to then switch the switch, i'm swaying towards the programmer as my first port as doing a bit more reading and what neily said alot of similar problems caused by the ST9400

 

[mickey dee]

Are there possibly any checks or links I can do to be certain it is the programmer or valve?

 

[Bolty123]

240 white and grey programmer is doing its thing. Take the head off spindle and see what happens.

 

[AWheating]

if the programmer was faulty and not switching you would not get voltage to the room stat and then the valve.

 

[mickey dee]

I have done some tests to elimate valve, I connected white and grey to PL and switched power on, valve moved over to CH and boiler fired and CH got hot. I then disconnected grey and white and connected to spare terminals then connected cylinder stat common from T6 to PL and switched on valve went to HW open boiler fired and pipe got hot
For CH and HW test connected white to PL put T6 back in original place, left grey in spare terminal, swiched on valve moved to mid position both HW and CH pipes hot. As these tests were pretty conclusive its gotta be programmer do you think?

 

[AWheating]

link out at the programer, if it works then change it.

 

[mickey dee]

Eventually got it sorted, it was a faulty head on the valve, got it replaced under warranty so happy to put it to bed, thanks all