Replacing Salus RT520TX wireless thermostat with Google Nest

14 Oct 2020
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United Kingdom
it's a Alpha E-Tec 33 combi boiler.

We have a Nest 3rd generation thermostat waiting to be installed and I was considering having a go installing it myself but just want to ask opinion on here first then decide whether or not to get a professional to do it.

There is a fused spur going into the Salus which then goes onto the boiler shown below.
Will all these cables fit into the Nest? And which slots do the COM & NO wires go into on the Nest?

My theory is: (Please see the attached images)
- existing blue/brown wires going into Salus L/N will go into corresponding L/N connectors of the Nest Heat Link
- single yellow/green wire going into NO/normally-open of Salus will go into connector 3/call-for-heat of Nest Heat Link
- jumper wire between L and COM/linked-live of Salus needs to be replicated, so put a jumper wire between L and 2/common of Nest Heat Link

Thanks in advance!
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20 Jul 2005
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United Kingdom
Sounds about right to me:

Salus N = Nest 3rd gen N

Salus L = Nest 3rd gen L

Salus NO = Nest 3rd gen 3 (heating call for heat) Note: It's not good practice to use a green / yellow wire as a live conductor, and as minimum it should have a brown sleeve over it.

Add a link between Nest 3rd gen L and 2 (heating common)

If you are going to connect the Nest Thermostat to T1 & T2 to provide it with operating power, the Heat link will also require and earth connection making to the earth terminal to the left of T1

Provided the Salus was connected correctly to the boiler, there's no need to change any wiring there. If the boiler has integral time control, it needs to be set to be permanently on 24/7.

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