Installing Nest in place of danfoss TP4000/vaillant - pictures attached

[saintamir]

See attached images:


I have a danfoss thermostat. It is currently installed in the hallway - I removed it and you can see the wiring behind it. It's a TP4000/TP5000 series.

The boiler is downstairs and has a switch besides it that you can see.

Question: How should I install the Nest heatlink and thermostat.

 

[stem]

First of all there is something odd here. I'm guessing the existing thermostat isn't working as the wires in your photo are in the wrong terminals. They are in N/C and Com, but......

........ they should be in Com and N/O. Do you have an explanation for this? It would be good to hear it before you proceed. But If you don't know, I suggest you get a pro in to check it out and find out what's happening at the other end of the cable and what it's connected to. Wired as it stands the heating would normally be working in reverse. 'On' when it should be 'Off', and 'Off' when it should be 'On'.

Also, you don't specify which version of the ecoFit Pure Vaillant boiler that you have. As you don't mention any hot water controls I assume that it's a 'combi boiler' and not a 'heat only boiler' with a separate hot water cylinder that you also wish to connect to the Nest.

Assuming it's confirmed the wires were originally in N/O and Com, if you have a Nest-e which is also battery operated like the existing thermostat then the wires would go to terminals C and N/O. It doesn't matter which way around, but convention has it that the brown wire is C.

Danfoss N/O = Nest-e N/O
Danfoss Com = Nest-e C

However, if instead you have a 3rd Gen Nest

Then the wires go Heating Common, terminal 2 and Heating Call for Heat terminal 3 [aka normally open or N/O]

Danfoss N/O = Nest (3) Heating Call for Heat [normally open or n/o]
Danfoss Com = Nest (2) Heating Common

However this version of Nest is not battery operated so it also needs a 230V mains supply connecting to N & L to provide it with operating power. This mains supply needs to come from the same 3A fused mains supply as the boiler.

 

[saintamir]

Thanks for the reply.

I don't have an explanation for the wires - they predate me (purchased property). If they were crossed it certainly explains why i think the current setup doesn't work.

How do you recommend I test for this?

It is a combi boiler.

I have the third gen nest. (not the e)

It seems like i should get the e instead to simplify things.

 

[stem]

Are you able to heat your radiators using the boiler as it stands?

What happens when you turn the thermostat up and down, i.e. does the heating come on when you turn it up, and go off when you turn the thermostat down?

 

[saintamir]

Yeah I can, the heating definitely works, i can heat up the radiators no problem.

Not sure the thermostat does anything I usually just smash its buttons it i feel the radiators up.. never worked out how it works reliably, so i could believe it if it was reversed.

 

[stem]

What happens when you turn the thermostat up and down, i.e. does the heating come on when you turn it up, and go off when you turn the thermostat down?

It's important to know what it's doing. It may not even be connected to anything at the other end. In which case any wiring advice would be useless.

1. With the thermostat turned up to maximum and the flame symbol showing.

Do the radiators heat up yes or no?

2. With the thermostat turned down to its lowest setting and the flame symbol not showing.

Do the radiators heat up yes or no?

You will have to allow time for the radiators to cool between tests.

 

[saintamir]

Thanks I'll try this after work today.