Please help with Nest Thermostat E that always calls for heat

Joined
19 Jul 2007
Messages
42
Reaction score
3
Location
London
Country
United Kingdom
Hi,

I'm trying to install a Nest Thermostat E but I can't get it to work properly - it always calls for heat. Its replacing a Danfoss RMT230 wired like this:

PXL_20220116_154933236.NIGHT.jpg


PXL_20220116_144001428.NIGHT.jpg


I wired in the Heatlink following the guide on this page:
https://support.google.com/googlenest/answer/9247634?hl=en-GB
PXL_20220116_104214020.jpg


Where it says terminal 1 on the Danfoss goes to C on the Heatlink, and terminal 2 goes to NO, so the Heatlink is wired in like this:
PXL_20220116_143940335.NIGHT.jpg


The old programmer is set to 'On' for Central Heating. Its a Danfoss FP715.

If I put the old thermostat back in the CH turns on and off depending on the temp setting as it should.

If I disconnect one of the wires from the Heatlink the CH stays off.

I've factory reset the Heatlink and the Thermostat E and re run the installation process, but it made no difference.

Any advice would be very gratefully received as I've no idea what to try next! Thanks for reading!
 
Sponsored Links

CBW

Joined
26 Sep 2019
Messages
11,510
Reaction score
3,210
Location
North
Country
United Kingdom
Could be a duff Nest? Do you have any test equipment?
 
Joined
15 Aug 2010
Messages
24,920
Reaction score
11,119
Location
Livingston
Country
United Kingdom
you have wired it correctly so more likely to be a setting that is telling the nest E to bring the heating on
 

CBW

Joined
26 Sep 2019
Messages
11,510
Reaction score
3,210
Location
North
Country
United Kingdom
I've got a multimeter, but that's about it.
That would work.
  • Select Volts Ac (sometimes denoted by a ~), and test between com and the blue (which appears neutral)
  • Then without demand test between the NO and blue
 
Joined
19 Jul 2007
Messages
42
Reaction score
3
Location
London
Country
United Kingdom
you have wired it correctly so more likely to be a setting that is telling the nest E to bring the heating on
Even with it set to 'Off' on the Thermostat E the heat remains on. Are there any other settings I should check?

That would work.
  • Select Volts Ac (sometimes denoted by a ~), and test between com and the blue (which appears neutral)
  • Then without demand test between the NO and blue
So swap it back to old Danfoss thermostat and try that? Will do, thanks! I'll report back with the result.
 
Joined
15 Aug 2010
Messages
24,920
Reaction score
11,119
Location
Livingston
Country
United Kingdom
remove the wires from NO and COM and test for continuity between the terminals with no demand for heating, if open circuit Nest is fine , if closed circuit nest is where the fault is,
 
Sponsored Links
Joined
19 Jul 2007
Messages
42
Reaction score
3
Location
London
Country
United Kingdom
remove the wires from NO and COM and test for continuity between the terminals with no demand for heating, if open circuit Nest is fine , if closed circuit nest is where the fault is,
Got it, thanks. I disconnected the wires from the Heatlink and did as you suggest. At the Heatlink there is always continuity between NO and COM regardless of whether the Thermostat E is asking for heat or set to off.

I can hear a clicking noise from the Heatlink when it changes to off - but there is still continuity. So it's knackered?
 
Joined
15 Aug 2010
Messages
24,920
Reaction score
11,119
Location
Livingston
Country
United Kingdom
Got it, thanks. I disconnected the wires from the Heatlink and did as you suggest. At the Heatlink there is always continuity between NO and COM regardless of whether the Thermostat E is asking for heat or set to off.

I can hear a clicking noise from the Heatlink when it changes to off - but there is still continuity. So it's knackered?[/QU
disconnect everything, if you still get continuity then yes the contacts are fused
 
Joined
19 Jul 2007
Messages
42
Reaction score
3
Location
London
Country
United Kingdom
disconnect everything, if you still get continuity then yes the contacts are fused
Got it, that's what I did. Looks like I'm sending it back.

@CBW @ianmcd Thanks very much to you both for your help with this its really appreciated! :)
 
Joined
20 Jul 2005
Messages
7,027
Reaction score
1,741
Location
Nottinghamshire
Country
United Kingdom
If you created a short circuit at some point during the installation, usually resulting in a blown fuse; what often happens is because of the excess current, the internal control contacts can weld together and create a permanently 'on' situation. Should this be the case, then you are responsible for the damage and the reason for the failure will be obvious should it be internally inspected when you send it back.

If nothing went wrong during the installation, then yes it's faulty, so send it back.
 
Joined
15 Aug 2010
Messages
24,920
Reaction score
11,119
Location
Livingston
Country
United Kingdom
If you created a short circuit at some point during the installation, usually resulting in a blown fuse; what often happens is because of the excess current, the internal control contacts can weld together and create a permanently 'on' situation. Should this be the case, then you are responsible for the damage and the reason for the failure will be obvious should it be internally inspected when you send it back.

If nothing went wrong during the installation, then yes it's faulty, so send it back.
@stem agree completely with what you say, but my experience with nest is they dont have anyone to check anything and they just send out a replacement, if you call as an installer they dont even want you to send the faulty one back, throw away culture these days
 
Sponsored Links
Top