Nest E wiring for zoned heating

12 Dec 2022
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United Kingdom
Hello, hoping someone can help. First time wiring a thermostat.

I currently have 2 zone heating (downstairs & upstairs). My setup is as follows:
System boiler (valliant)
Megaflo hot water tank
Honeywell valves for each zone
Programmer for heating and hot water where the heating is set to constantly 'on'
2 Heatmiser touch thermostats to control each zone - upstairs and downstairs

I am looking to replace the upstairs thermostat with a Nest E but I am not sure which of the wires need to be connected to Common and NO ports on the nest e thermostat.

I have attached an image of the current wiring to the heatmiser thermostat and a screenshot from the heatmiser manual with wiring guide.

Based on this should A1 be connected common and A2 connected to NO with L and N being terminated?

Apreciate any help. Thanks!


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looks like you have sussed it.

A1 = COM
A2 = NO

Nest-e is battery powered, so the 230V supply in N & L are not required and should be safely insulated and isolated. They should not be connected to the Nest.
Thank you for your help confirming this

I was thrown by the Nest website which suggests different connections for replacing Heatmiser thermostats and really confused me (screenshot below highlighted in blue).

I assume this my apply when the Heatmiser is wired for a different type of heating system setup

The clue is in the diagram on the back of the thermostat. A1 & A2 are simply an on/off switch. When the thermostat is 'on' the two terminals are electrically connected by the internal switch.


Which corresponds with Nest-e C (Common) and NO (Normally Open) which are the electrical terms for an on/off switch. When the Nest-e is 'on' C and NO are electrically connected by an internal switch.

I suspect your Neostat is the one underneath, Version 2.


As it's a simple on/off switch it doesn't matter really which way around the two wires go, although convention dictates that the contact that moves is the common and the one that is fixed is NO. So actually I told you the wrong way around when I said

A1 = COM
A2 = NO

But in reality it doesn't really matter it will work either way around.
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Thank you again this is really useful and makes sense to me now :)

My Nest E is on order and should arrive in the next few days. Will get it setup as suggested.

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