Can you post a photo of the receiver wiring? It's very odd that it can't override the programmer and switch the heating off.
Programmer/stat not controlling heating - trying to make sense of wiring?
- Thread starter Jason90
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Thanks, now with the programmer back up on the wall and this time the thermostat receiver removed from it's backplate does the boiler run at all for heating. It shouldn't be able to, whatever you try at the programmer.
While its removed you should also check the voltage on the grey wire at terminal 3 of the receiver backplate both with heating set to ON and then to OFF by the programmer.
It should be 230V for ON and something closer to zero when heating is set to OFF.
While its removed you should also check the voltage on the grey wire at terminal 3 of the receiver backplate both with heating set to ON and then to OFF by the programmer.
It should be 230V for ON and something closer to zero when heating is set to OFF.
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Looking at the pic of the wiring centre, the grey from the valve (black cable) appears to connect to terminal 7, but there is nothing else connected to T7. Is this correct? It's very difficult to trace all the wires - even with it blow up.
The strange voltages, 185 on orange etc., do not mean the valve is faulty. They are quite normal and a feature of the way a mid-position valve works.
A mid-position valve always stops in the position last used. So if HW is last to turn off the valve stops in HW (port B open); and if CH was last to turn of the valve stops with Port A open. This is true eve with the valve in mid-position as, even then, either CH or HW will be last to turn off.
HW Only is no problem as the valve is not in circuit; the boiler switched live comes from the HW thermostat Call terminal. This is also true when HW and CH are both on and the valve is in mid-position But when the valve is in CH only the boiler is fed from the valve's orange wire. So if CH is last on, so the valve stays with Port A open, when CH is turned off there will still be a voltage on the orange wire. In some cases this voltage is sufficient to turn the boiler on.
Here's how to check:
1. Set CH and HW off at programmer
2. Turn CH and HW thermostats down
3. Now turn power to the heating system off (setting programmer to HW and CH off is not sufficient)
4. Turn power back on
5. Turn HW On at programmer.
6. Turn HW stat up and down. The boiler should go on and off and pipe from valve to cylinder get hot.
7. Leave HW stat turned up
8. Turn CH on at programmer
9. Turn Room stat up. Valve should move to mid-position. Pipe from valve to rads and valve to cylinder should both get hot.
10. Leave room stat up and turn cylinder stat down. Pipe to rads should stay hot and pipe to cylinder cool down.
11. Turn room stat down. Boiler should go off and pipe to rads cool down
12. Turn room stat up. Boiler should light and pipe to rads get hot
13.Turn CH off at programmer. Boiler should go out and pipe to rads cool down.
If the boiler continues to run at 11 and 13, the problem is in the boiler.
The strange voltages, 185 on orange etc., do not mean the valve is faulty. They are quite normal and a feature of the way a mid-position valve works.
A mid-position valve always stops in the position last used. So if HW is last to turn off the valve stops in HW (port B open); and if CH was last to turn of the valve stops with Port A open. This is true eve with the valve in mid-position as, even then, either CH or HW will be last to turn off.
HW Only is no problem as the valve is not in circuit; the boiler switched live comes from the HW thermostat Call terminal. This is also true when HW and CH are both on and the valve is in mid-position But when the valve is in CH only the boiler is fed from the valve's orange wire. So if CH is last on, so the valve stays with Port A open, when CH is turned off there will still be a voltage on the orange wire. In some cases this voltage is sufficient to turn the boiler on.
Here's how to check:
1. Set CH and HW off at programmer
2. Turn CH and HW thermostats down
3. Now turn power to the heating system off (setting programmer to HW and CH off is not sufficient)
4. Turn power back on
5. Turn HW On at programmer.
6. Turn HW stat up and down. The boiler should go on and off and pipe from valve to cylinder get hot.
7. Leave HW stat turned up
8. Turn CH on at programmer
9. Turn Room stat up. Valve should move to mid-position. Pipe from valve to rads and valve to cylinder should both get hot.
10. Leave room stat up and turn cylinder stat down. Pipe to rads should stay hot and pipe to cylinder cool down.
11. Turn room stat down. Boiler should go off and pipe to rads cool down
12. Turn room stat up. Boiler should light and pipe to rads get hot
13.Turn CH off at programmer. Boiler should go out and pipe to rads cool down.
If the boiler continues to run at 11 and 13, the problem is in the boiler.
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T7 is liked to T8 and T16. The link is bare copper from 7-8.
At the top, near the red links? Well spotted.
I remember getting a belt off of one of those bare links once! 
After seeing such a high voltage it sounds quite similar to this issue - //www.diynot.com/diy/threads/hive-wired-wrong.418141/page-2
Is it possible this 120v is triggering the boiler to stay on?
Is it possible this 120v is triggering the boiler to stay on?
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What make and model boiler have you got?....Worcester by any chance???
120V is quite high, the boiler sensing circuit must be rather high impedance. You didn't used to get this problem when the signal to fire directly powered the gas valve! If it is that, there are some ways around it, a snubber network can be fitted between the orange wire and neutral, this usually corrects the issue. Or the controls can be used to switch a relay on, it's contacts switching the boiler.
It's a British Gas 330 which seems to be a rebadged Glow-worm HXI something or other
Amateur hour now - what is a snubber network and when you say fit it across orange and neutral is that the orange and neutral of the mid-position valve back in the wiring centre?
Sorry, one more q - why on earth would this start happening now after the system has been installed about 9 years ago?
Snubber is just a capacitor and resistor in series, usually 100μF capacitor and 100Ω resistor. Neat wire ended versions are made. They can sort all sorts of issues. Yes for connection. Wooster have a module to correct the problem with Y plans that trigger some of their models. I've never seen the module or what's inside it though.
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A capacitor across SwL/neutral is the fix when using mid position valves (100 volt @ SwL) , Worcester now incorporate the capacitor within the control board.
If that is the cause of the problem you could try the 0.1uf 500V capacitor from Maplin linked in the above thread.
It just goes between the valve orange and blue connectors and for the sake of a few quid it's worth a try.
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