Nest Wiring issues 3rd Generation

[Dan Bate]

I have a Nest 3rd Generation heatlink and thermostat which is connected to a y plan system that includes a Baxi solo boiler, grundfos pump and a Drayton mid point actuator all wired as labelled through a Drayton LWC1.
My issue is that regardless of what I do the heating is on. The thermostat is wired with two wires out of the T1 and T2 terminals and is on but the heating ring has no effect on the heating. If I turn the fuse on the pump immediately fires up and the heating comes on. If I boost or schedule the hot water to come on it moves the mid point actuator to the middle (which isn't labelled but I suspect is for HW and CH).
Then if I stop the schedule or boost for HW the pump switches off and then fires straight back up continually for the CH.
I have tried all sorts to fix this and the problem I think comes from the heat link. The terminal for 3 'Heating Relay Normally Open' is continually live regardless of what the temp is set at in the app or if it turn the system off and on manually. I hear the click of the relay but the live doesn't change. To my mind the heatlink is constantly asking for heat?? I may be wrong.
Any help is more than appreciated.
Thanks

 

[jackthom]

You are correct that terminal 3 should only be Live when heating is called for.

I would be inclined to temporarily disconnect the wire from that terminal and then see if the heating remains On or goes Off.

It’s possible there is a wiring problem somewhere and the wire you remove from heat link #3 may still be getting a permanent Live from elsewhere.

 

[Dan Bate]

Pictures of the heatlink showing live on terminal 3

 

[Dan Bate]

Heat Link Wiring

 

[jackthom]

If the Heatlink terminal 3 is still permanently Live with its wire removed the problem is with the Nest itself.

 

[Deleted member 267285]

3 comes from the white wire from your 3 port, have you checked this? Can you post photos of wiring center?

 

[Dan Bate]

The wiring centre,
1 = Empty
2 = Links with 3 to remove the old thermostat
3 = As above
4 = Goes to the actuator - white wire
5 =Empty
6 = Goes to the actuator - Orange wire
7 = Goes to the actuator - Grey Wire
8 = Hot water off goes to terminal 4 on the Heatlink
9 = Central Heating On goes to terminal 3 on the heatlink
10 = Hot water on goes to terminal 6 on the heatlink
11 = Boiler L Goes off to the boiler
12 = Boiler switched live.Goes off to the boiler
13 = Pump live. Goes off to the pump
14 = Cylinder wire.
15 = Cylinder wire.
16 = Cylinder wire.

 

[Dan Bate]

Wiring Centre

 

[stem]

If I boost or schedule the hot water to come on it moves the mid point actuator to the middle (which isn't labelled but I suspect is for HW and CH).

The mid position does indeed indicates that the controls are asking for both CH and HW.

Then if I stop the schedule or boost for HW the pump switches off and then fires straight back up continually for the CH.

That will be the boiler switched live [which is also directly connected to the pump live via the link between WC 12 & 13] switching off, and then a slight delay whilst the motorised valve moves to the heating position at which point it operates a microswitch and the switched live is restored.

To my mind the heatlink is constantly asking for heat??

That is the usual conclusion I would make.

Having followed the wiring centre connections, the live to the motorised valve white wire (Heating On) does come directly from the Heat link terminal 3 as it should, albeit via a rather tortuous route:

HL 3 -> WC 9 -> WC 3 -> WC 2 -> WC 4 -> MV white wire

I can't see another wire connected to any of these terminals from anywhere else that could introduce a rogue live, so as has already been said, try removing the grey wire from HL 3. If the heating doesn't come on with the wire removed, there is a problem with the HL. If it doesn't, the only other possibility I can think of is that there is a wiring fault inside the motorised valve that is somehow introducing a live on the white wire from one of the other wires internally.

Based on your photo and descriptions, the rest of the connections at the wiring centre are as I would expect them to be. However, I notice that the wire you describe as "Boiler L" [in WC 11] isn't actually connected to anything, which could be OK; older Baxi Solo's certainly should have a permanent L, but maybe your model doesn't. In any event, it wouldn't produce the symptoms you describe.

Did everything work correctly before the Nest was installed? and are the only changes you have made been the addition of the brown link between WC 2 & 3 and moving the brown, grey and black wires that originate from WC 8, 9 & 10 from the original programmer to the HL?

Have you blown any fuses during the installation process? A short circuit can sometimes cause 'switching contacts' to weld together.

 

[Deleted member 267285]

@stem could boiler switched live and heating call (NO) be the wrong way around at heat link? At the WC there is sleeving at 12 and not at 9, I know it might just be wired like that, but was just wondering?

 

[Dan Bate]

@stem
If I remove 3 from the heatlink the heating doesn't come on and I can control the hot water.
The Boiler is picking up a permanent live in 11 from a red wire hidden behind in the photo. Its coming from the vertical junction box from the feed into the wiring centre
There wasn't a fuse blown.
The heating was working with its previous system and I can get the hot water to do what I want but not the CH.
I will post a photo taken before I began doing anything

@CBW
I believe that is the same wire it just doesn't have the black cover at the one end for whatever reason. The core doesn't have two grey wires in it and I can trace from the Heatlink to the wiring centre.

Both Thank you for your help. Its all really appreciated

 

[stem]

@stem could boiler switched live and heating call (NO) be the wrong way around at heat link? At the WC there is sleeving at 12 and not at 9, I know it might just be wired like that, but was just wondering?

I wouldn't have thought so, the 'heating call' grey wire in 9 is contained in the same cable as the brown and black wires going to the Heat link and the grey wire in 12 is in the same cable as the other boiler wires.

 

[stem]

If I remove 3 from the heatlink the heating doesn't come on and I can control the hot water.

Then the problem is with the Heat link. Terminal 3 should only be made live when the Nest tells it to switch the heating on.

 

[Deleted member 267285]

Then the problem is with the Heat link. Terminal 3 should only be made live when the Nest tells it to switch the heating on.

Sorry, I’m lost with this. The heating isn’t coming on if the wire is removed (I understand that), he can control the hot water from Nest (i understand that), issue with the Nest (I don’t understand that).

 

[Deleted member 267285]

@stem
If I remove 3 from the heatlink the heating doesn't come on and I can control the hot water.
The Boiler is picking up a permanent live in 11 from a red wire hidden behind in the photo. Its coming from the vertical junction box from the feed into the wiring centre
There wasn't a fuse blown.
The heating was working with its previous system and I can get the hot water to do what I want but not the CH.
I will post a photo taken before I began doing anything

@CBW
I believe that is the same wire it just doesn't have the black cover at the one end for whatever reason. The core doesn't have two grey wires in it and I can trace from the Heatlink to the wiring centre.

Both Thank you for your help. Its all really appreciated

On this photo, the crimped wire is going to number 10 in WC, yet number 6 on other photos?