HELP....No mid position on Honeywell 4073A

[icarte01]

Right....

Heating works fine......
Water works fine...
But if the boiler calls for water when the heating is on, the water does not heat up.
Basically we have to turn the heating down for the water to warm up. I have check the mid position valve and it seems that I am not loosing the 240V on the Grey wire that sends the valve to Mid position. There is always 240V on white and grey when heating is on. If I remove the grey wire the valve does move to the Mid position

Any helps would be greatly appreciated

Thanks

Ian

 

[stem]

Basically, I think you've answered your own question. The grey wire should only be live when hot water is not required. When the central heating is on, a live on the grey winds the motorised valve over to the central heating only position. This live on the grey comes from two places.

1) The' hot water off' terminal from the programmer which is live except when the hot water time setting is selected on.

2) The changeover contact on the hot water thermostat, it puts a live on the grey when the hot water is selected on, but is up to temperature.

Assuming that it is wired properly and has worked in the past, you need to find out which one of the two is keeping it live. If you can do it safely, isolate the electricity and then disconnect the 'hot water off' connection from the programmer. (Be careful because the disconnected cable could still be live if it's being fed from the cylinder when you turn the power back on) If the grey is still live when you turn the power back on, repeat the process for the hot water satisfied contact from the cylinder thermostat.

Whichever results in the loss of the live on the grey, that's where the fault lies. If neither result in a loss of the live, you likely have it wired wrongly.

 

[icarte01]

Thanks for your time

I was thinking about the tank stat but will also check the programmer

Ian

 

[oilhead]

I have the same with a customer, but replacing the cylinder stat with a connector block looped, and disconnecting the HW off from the junction box has not solved the problem. One of Honeywell technical staff says there could be a problem with the circuitry in the valve, another says not. Changing the head has made no difference!!

 

[stem]

Oilhead, I think in this case, the valve is working OK, when the central heating is 'on' and grey is not live, the valve does take the central position, as it should. It's why the grey wire remains permanently live that is the problem.

icarte01, reading your post again something is strange here. It is unlikely to be the 'hot water off' at the programmer that is at fault, because if it was live all the time, switching the central heating thermostat down wouldn't have any effect on that.

On the other hand, if the cylinder thermostat was stuck in the satisfied position, when the central heating was turned off, the cylinder stat wouldn't switch on the boiler and you still wouldn't get any hot water either.

So it's going to be a matter of tracing that grey and finding out where it's getting its live from. When you do find out what's causing it, can you post back on here what the problem was please, I'm intrigued.

 

[DeltaT]

This link may help you both understand better;
http://octaveblue.co.uk/c_heating/index.htm