Thermostat only turns on heating after I set temperature below room temperature

[Aaronjiang]

Hi I recently moved in to a flat where it only got a nest heat link so I bought a nest thermostat. But after I configured everything it turned out that it only turns on heating when I set the temperature below room temperature and turned off heating when I set temperature above room temperature. I have a combi boiler. What should I do?

[Frustratedddd]

This can be a tricky one.

What is the reading on the display before you change the setting to call for heat? Low for example like 10 - 14?

The base plate for the display, was that in the flat also or did you buy that to? Was it an ebay purchase?

[Aaronjiang]

Thanks for your reply. My current reading displays current room temperature. For example if the current room temperature is 24 C, if I set the target temperature to below 24, heating would be turned on while if I set the the target temperature to above 24, heating would be turned off. I bought the whole unit on eBay

[Frustratedddd]

Just to confirm, the heat link was in the flat when you arrived, nothing touched on the heat link, then you purchased the display and base plate from ebay correct?

Can you confirm the connections on the heat link, terminals 1 - 2 - 3, or better still a picture of the connections. This might be as simple as incorrect wiring.

[Aaronjiang]

Yes that’s correct. The heat link was here when I purchased the flat and I only bought the thermostat (black round thingy with display) and connected to the heatlink wirelessly.

I don’t know how to insert a picture here can I send you an email? Or if I describe it there is a blue one goes into N, brown one goes into L, grey one goes into 1 and black one goes into 2

[Frustratedddd]

That sort of sounds OK, except  1 - 2 terms might be an issue

I think you are switching the wrong contacts.

Term 1 should be into term 3 - BUT show me a picture before that is done. You also need to prove which core is the live feed out of term 1 or 2. A simple neon screwdriver can prove that, or any form of simple tester will do. Be aware it is live in there!!

Upload a picture by clicking on the camera icon, you have to be logged in to do that.

[Aaronjiang]

 thanks! Please find the photo attached!

[Frustratedddd]

Wired wrong!

I don't really know where to start, but whoever installed that needs shooting! Disgraceful.

1st. The cable feeding the heat link is NOT visible, just the cores are held by the clamp. Wrong!

2nd. The cores are not covered outside the heat link. Wrong!

3rd. No Earth connection or any visible Earth protecting the main cable visible. Wrong!

4th. Bare copper showing in the terminations. Wrong!

5th. Connection incorrect, wired in the wrong termination. Wrong!

Other than those few items I cannot see any problems with the installation.

Assuming you can rectify the above, and assuming the Black core is a permanant live feed. Swap termination 1 into termination 3.

These are assumptions, and as mentioned before, you need to prove Black is a permanant live feed. Should Grey be the permanant feed then that would be another configuration.

Oh dear, who wired that, as I would check ALL of the install if I was you? I would put money on the terminations being loose also. Sorry to be harsh, but the amount of bodgers about today is shocking! Or could be!

[Aaronjiang]

Have no idea who installed this maybe this is why the thermostat was not installed in the first place! Think I might just try to rectify this myself. So how to prove whether black is live? Is it like if I put the neon screwdriver to the copper bit and if it is glowing then it is the live one and if it does not glow then it is not?

When I reconfigure this, do I just unscrew the screw on the grey one so that I can pull out the copper and insert that into 3 then screw? Many thanks! 

[Frustratedddd · Accepted solution]

😂😂Oh dear this is worrying!

How are you going to get the most important connection to the Heat link, the Earth wire? The other wires only make it work.

You shouldn't be able to see any copper which is the main point, but if you place the neon onto the termination screw, then you can test for live. Make sure the heat link just has the one light on, and the thermostat is NOT turning the boiler on. Your case would be to turn the thermostat up to above room temp. This proves that term 1 should be no power, and term 2 should be live. To confirm that is correct, Term 3 should also be live in that state.

Neon has light = Live

Neon has NO light = No Power

Yes, just swap from Term 1 to Term 3.

Like I said, sorry for being harsh, but bad wiring can cause fires. let this be a lesson for all the people who read this post, and who congratulate themselves for getting the thermostat working, but is it safe?

I have also added a picture of the correct wiring. This is a very simple job, but leaving the setup as you have is NOT good. Yes you can connect and it will work, but is it correctly installed, NO?

[Aaronjiang]

Thanks man, it works now!!

[Frustratedddd]

Oh well so long as it works, may not be safe but works!!! 🔥