Stat / Wiring Problem


Postby Parts Man » Sat Nov 24, 2007 5:43 pm

Moved into our house in the summer and all fine. Now winters here and we have a problem.
The central heating will only work / run until the hot water tank reaches temp. then the boiler and pump shut off. Next door neighbour says his does the same.
I can 'make' it come back on by running off the hot water but it shouldnt be like that and now its bugging me.
Have checked the system as follows - With boiler / pump running turn room stat down - mid position valve moves to h/water only. Turn stat back up valve moves back to mid position.
When the tank is fully heated the mid position valve stays in mid and the pump and boiler shut down till the tank cools.
As far as i can tell it all seems to be running correctly so i looked into the wiring in the junction box.
I seem to have a grey wire from the mid position valve which is not connected to anything the end of which is insulated with tape :?:
Any ideas
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Postby marrtin » Sun Nov 25, 2007 12:05 am

Obviously, there are several different wiring systems for central heating so it is difficult to be exactly sure how it needs wiring.

The grey wire supplies 230v to the mv when the water has reached temperature, which in turn moves the valve to the CH only position. I would have thought that if this connection was omitted, the hot water would have continued to be heated whilst the room stat was calling for heat.

This suggests that the wiring may not be a true Y plan. Check the wiring with the Honeywell website.


The grey would normally connect to pin 2 of the cylinder stat and the N/O contacts of the programmer.

Remember that all these circuits are at 230v mains voltage. Please do not attempt any alteration unless you are confident at working with electricity.
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