Is this plan to install a Nest thermostat correct on a Valiant boiler?

10 Oct 2019
Reaction score
United Kingdom
Hello, just want to be sure I'm getting this right. Combi boiler does not currently have a thermostat and I'll be using a Nest stand.

Nest heatlink to boiler (Valiant Turbomax 242/1)

N grey (neutral) to 5
L Brown (live) to 3
3 Black (sw live) to 4
And loop wire between L and 2 on the heatlink.

Probably a daft question but I want to be sure; do I need to run power from the mains to the heatlink too or does the heatlink get powered from what is written above, ie just one 3 core cable running between the heatlink to the boiler?

Last edited:
Sponsored Links
Heat Link to boiler...

N to N
L to L
2 to 3
3 to 4

No link needed between L and 2
What you suggest is OK. You don't need a separate live, as boiler terminal (3) provides it. The only exception might be if the boiler has integral time control, in which case set it to be permanently 'on'

Just be careful if you have to open up a room sealed compartment to access the boiler wiring terminals (some boiler's you do some you don't) if you do, it's a job for an RGI, as they can do the tests to make sure it's safely sealed afterwards.

Just noticed I was pipped to the post.....Or you could do it as muggles suggests (there is more than one way to skin a cat)
Last edited:
Sponsored Links
Thanks for the help!

The boiler does have and integral timer, which I was planning on leaving in the on position yes. Does that affect Muggles' suggestion?

Also luckily the wiring on this boiler is in unsealed compartment.
Often the boiler timeswitch turns the live supply to the external controls on & off, (In your case boiler terminal 3). If it does, the boiler timeswitch will need to be 'on' for either way of wiring it to allow the Nest to start the boiler.

Therefore, with what you proposed if the timer was 'off' the Heat link would probably loose power too, with what Muggles suggests, the Heat link would stay powered but still wouldn't start the boiler.

luckily the wiring on this boiler is in unsealed compartment.
I thought it might be, otherwise Muggles would have mentioned it, he seems to know most boilers.

There is a way around it if you can safely check with a multimeter to see if the timeswitch does turn the live boiler terminal (3) on and off. But if you are happy to leave the timeswitch on 24/7 don't worry about it.
So all connected and working fine, but stuffing two wires into the each N an L terminal on the boiler was very difficult and I'm not totally happy leaving it like that, as its almost impossible to get the two wires neatly, equally in with no uninsulated wire visible.

The 3 way Wago connectors suitable for making a tidier job? Can't imagine why not, but best to check eh.
Yes, a couple of 3-terminal Wago connectors would certainly do the job

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links