Combi boiler stat not turning off heating

[Matt0029]

If the stat is not shutting off a combi boiler (analogue stat Honeywell) even though the stat is clicking when turned up above the room temperature. What are the likely causes. Unless it's never been wired right from the start up. Thanks.

 

[Deleted member 120897]

Thanks so testing neutral to live in. With a reading of 240vac between the ports. Shows I am getting 240vac to the stat.

Yes correct, but doesn’t prove it works properly, hence the additional testing and don’t forget the link.

 

[Deleted member 120897]

Does testing neutral to switch live on demand with a reading of 240ac show that switch live is sending power to the boiler. Making a circuit when there is a call for heat?

Yes

 

[ShaunCorbs]

Test terminal 3 to earth or neutral with stat off should be no voltage

If there is 240v check 1 if that’s got 240v aswell stats dead

 

[Matt0029]

Yes correct, but doesn’t prove it works properly, hence the additional testing and don’t forget the link.

Thanks yes I will make sure it's wired in to the boiler.

 

[Matt0029]

Thanks just trying to find the wiring diagram. I think Live is 1. Neutral 3. Switch live 2. ?

 

[Deleted member 120897]

Thanks just trying to find the wiring diagram. I think Live is 1. Neutral 3. Switch live 2. ?

No:

1 should be live in
3 should be switched
2 should be Neutral

Wiring diagram usually on the reverse of stat cover.

 

[Matt0029]

Thank you

 

[Matt0029]

No:

1 should be live in
3 should be switched
2 should be Neutral

Wiring diagram usually on the reverse of stat cover.

Thanks what Shaun said to test makes more sense now!

 

[Matt0029]

Test terminal 3 to earth or neutral with stat off should be no voltage

If there is 240v check 1 if that’s got 240v aswell stats dead

To to check I'm on the right track. Testing 3 (switched) to earth or neutral with the stat off. A reading of 0v. Shows that no volts are passing though the circuit i.e no call for heat at the boiler?

 

[ShaunCorbs]

Correct but I have seen them wired backwards eg 3 live 1 switch

 

[Deleted member 120897]

Correct but I have seen them wired backwards eg 3 live 1 switch

Yep, me too. Had one recently, set to a mid point, so in winter it’s fine. The way it was wired max was off and low (5 degrees) on the VRT30 was off.

 

[Matt0029]

Correct but I have seen them wired backwards eg 3 live 1 switch

Thank you!

 

[Matt0029]

Correct but I have seen them wired backwards eg 3 live 1 switch

Thanks of wired backwards at the stat it would still work? I know if get the wires wrong when swapping a boiler at the boiler side the stat comes on when turned down and off when turned up.

 

[Matt0029]

Test terminal 3 to earth or neutral with stat off should be no voltage

If there is 240v check 1 if that’s got 240v aswell stats dead

If that stat was dead, would that cause it not to knock off the heating. As is happening. Thanks

 

[ShaunCorbs]

Yes they can stick eg on all the time