Heat link wiring to Honeywell Smartfit

11 Feb 2022
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United Kingdom

I’ve read multiple posts about installing the Nest Heat Link to the Honeywell Smartfit.

However I seem to be struggling on how to physically wire it up.

The attached photo is how the smartfit is wired up currently with everything working.

Can anyone offer some advice and guidance on how to wire the heat link upto the system?




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I’ve read multiple posts about installing the Nest Heat Link to the Honeywell Smartfit
Have you read this one, saying nest isn't compatible with your Smartfit?


Another link here:


And some further information:


Basically, it seems to be a case of replacing the proprietary smartfit valve heads and starting again, or using a workaround using some resistors to create a false reading for the Honeywells thermistors.
Good luck! :confused:
Last edited:
I seem to remember that the Smartfit motorised valves were extra low voltage, seem to remember 24 volt but may be wrong, and the tank does not have a thermostat but a temperature sensor.

The major problem is the cables are for extra low voltage, and the voltage was taken from the Smartfit.

So new motorised valves and new tank thermostat plus likely new wiring.

And to swap to Nest that is out of the frying pan into the fire, Nest also seems to have been abandoned in the UK. It is about the only smart system that does not either work multi zone valves or TRV heads, I cross my fingers and hope the temperature sensors will be released in the UK, but as yet only released for USA.

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