Central heating not being triggered by control panel

[stem]

Firstly with the originally wiring as the motorised valve never goes to H.

If it never goes to 'H' then it will never trigger the microswitch, so the microswitch is probably OK, just not being operated as the valve doesn't reach it. Which is why I said before doing the test to first....

check that the valve has moved to the heating only position.

So sorry, if I have confused you with a red herring, I got a bit muddled about what was happening with the positioning of the valve from the earlier posts.

If the valve doesn't go all the way to H. Then as has been mentioned I would check for a live on the motorised valve's grey wire (hot water not required) whilst the hot water is 'off' and the heating 'on'. The live on the grey wire is the signal that is responsible for moving the valve from the 'mid position' to 'CH'. If that live is present, and the valve is still in the mid position, then the valve is faulty, probably SW1.

 

[Harry Bloomfield]

Yes CH works when i call for both.. The boiler and pump just won’t fire when CH is requested by itself.
What tells the boiler to fire up? I assume the programmer and room stat, then the boiler and actuator/valve react? Or am I misunderstanding?

You are misunderstanding - This is the order programmer > room stat > valve actuator > boiler + pump. The valve actuator is the last link in the chain and needs to move to the CH position. Actuators are the weakest item in the chain and often fail. I always keep a spare to hand, ready to swap out. Motors fail, the mechanisms can stick, the microswitches can fail.

 

[ianmcd]

You are misunderstanding - This is the order programmer > room stat > valve actuator > boiler + pump. The valve actuator is the last link in the chain and needs to move to the CH position. Actuators are the weakest item in the chain and often fail. I always keep a spare to hand, ready to swap out. Motors fail, the mechanisms can stick, the microswitches can fail.

There is nothing wrong with the motor read the whole post

 

[Harry Bloomfield]

There is nothing wrong with the motor read the whole post

I didn't suggest there was, read my post.

 

[D_Hailsham]

Both the HW and CH have worked fine and independently up until yesterday evening.. Now the HW works fine, turns on as it should and fires up the boiler and I have hot water. However if I turn the HW off and just turn the CH on the boiler doesn’t fire up.

For heating to work on its own there must be voltage on both white and grey wires. The white wire is powered from the programmer CH on terminal, via the room thermostat. The grey wire can be powered in two ways:

1. From the programmer HW OFF terminal
2. From the programmer HW ON terminal via the cylinder stat 'Satisfied' terminal, i.e HW has reached the required temperature.

You appear to be testing CH only by turning HW OFF at the programmer, i.e method 1. However it's not unknown for systems to be wired so only option 2 works (only requires a 2-core cable to the cylinder stat).

You need to test option 2 by leaving the programmer HW ON and then turn the cylinder stat down to minimum. If CH turns on the valve is OK; there is a problem with the Programmer HW OFF terminal or a missing wire between HW OFF and the valve's grey wire.

This FAQ has more info about how a mid position valve works and how to test it.

 

[Benillsley]

Ive attached images of the programmer wiring, junction box and results of testing the actuator voltages.

 

[Benillsley]

You need to test option 2 by leaving the programmer HW ON and then turn the cylinder stat down to minimum. If CH turns on the valve is OK; there is a problem with the Programmer HW OFF terminal or a missing wire between HW OFF and the valve's grey wire.

This FAQ has more info about how a mid position valve works and how to test it.

Just tried this and having both CH and HW on the programmer, turned the cylinder stat right down and the boiler turned off.

Also checked the output with only CH on from the Programmer In the junction box and got 240volts

 

[Benillsley]

post a pic of the wiring of your programmer, when the programmer is set to CH only the valve should motor to H, and then the microswitch will power the boiler, but you need a HW off signal for this to happen, so either your programmer is not switching the HW off terminal or more likely it has never been wired in and that is why the valve was latched in the first place

With only CH turned on the HW off terminal (pin 8 on junction box) is showing 240v

sorry for the multiple replies, just trying to cover everyone’s very helpful suggestions!

 

[Benillsley]

Because the HW off is not wired correctly

Pin 1 (HW off)from the programmer goes to number 8 on the junction box and the grey wire (HW off) from the valve goes to number 7. These are as per the attached wiring diagram.

Or am I still missing something?

 

[stem]

Thanks for the pictures, however, if it used to work OK and you haven't changed the wiring, I wouldn't expect anything to be amiss. I'm, still a bit confused by a couple of your posts, but it will probably be me not grasping the sentiment.

So here's how I test a 3-Port valve, only do it if you are able to try it safely. If in any doubt don't proceed. It will only work if you follow the instructions in the order given, to the letter & skipping those you are asked to. Don't rush. As the valve has been moving during your previous trials, I have not included testing of the motorised valve neutral. [For best results, the tests should be done with a multimeter & not a voltage stick.]

1) Turn off the mains power to the entire heating system at the fused spur (not just at the programmer) The valve should be in the hot water position, is it?

• If no, the valve is faulty
• If yes, is go to 2

2) Make sure the heating and hot water are 'off' at the programmer and that the cylinder thermostat is 'on' before restoring the mains power. Then check the grey wire going to the motorised valve, is it live?

• If no, there is a wiring fault somewhere, or the programmer is faulty, report back
• If yes, proceed to 3

3) Now turn the cylinder thermostat 'off' and the hot water only 'on' at the programmer. Check the grey wire going to the motorised valve, is it live?

• If no, there is a wiring fault somewhere, or the cylinder thermostat is faulty, report back
• If yes, proceed to 4

4) With hot water only 'on' at the programmer turn up the cylinder thermostat high enough so that the boiler fires. The valve should still be in the hot water position. is it?

• If no, there is a wiring fault somewhere, report back
• If yes, proceed to 5

5) With the boiler running from the previous test, now turn on the heating at the programmer, and make sure the room thermostat is also 'on'. The valve should move to the mid position. Does it?

• Only if it remains in the hot water position, check for a live on the motorised valve's white wire. If it is live, the valve is faulty. If not, there's a fault with the programmer or room thermostat. Report back
• If it's moved to the mid position, proceed to 6

6) Leave the heating on at the programmer and room stat, and turn off the hot water at the programmer and cylinder thermostat. The valve should now move to the heating only position. Does it?

• Only if yes, go to 7
• If no, go to 8

7) Without changing anything, check for a live on the motorised valve's orange wire. Is it live?

• If yes, the valve is working as it should be.

8) Without changing anything, check for a live on the motorised valve's white and grey wires. Are they both live?

• If yes, the valve is faulty.

 

[Benillsley]

Thank you for the comprehensive reply and advice!
I’ll test when I’m home tonight and report back.
I actually have a new actuator/valve head now too which I can try after carrying out your tests.

 

[Benillsley]

So following the above steps my results were:
1.Yes
2.yes
3.yes
4.yes
5.mid
6.no
8.yes

Fortunately I had ordered a new actuator earlier in the week which I’ve just fitted and I have heating again! All working as it should.
Huge thanks to everyone for your help especially you @stem, your fool proof step by step really helped, thanks a bunch mate!

 

[Harry Bloomfield]

Fortunately I had ordered a new actuator earlier in the week which I’ve just fitted and I have heating again! All working as it should.
Huge thanks to everyone for your help especially you @stem, your fool proof step by step really helped, thanks a bunch mate!

Having saved yourself a nice wedge of cash for an engineer - rather than it being a urgent distress purchase next time, buy yourself a spare actuator.