Horstmann C21 replace with Nest Gen 3 Heat Link

[CharlieDIY]

Hi,

I'm trying to replace my Horstmann C21 with the Gen 3 Heat Link.

Feeling slightly confused right now and was hoping for some help.

I've got N L 1 3 4 connected on the Horstmann, where would these connect onto the Heat Link?

Please see attached picture of current setup!

 

[stem]

It's quite straight forward, you simply identify each wire from where it is presently connected at the Horstmann and move it to the corresponding terminal at the Nest Heatlink

If you look at the Horstmann C21 the wires are identified as below. They connect to the terminals at the Nest that have the same function.

Horstmann N Neutral goes to........Heatlink Neutral N

Horstmann L Live goes to.......Heatlink Live L, and it should also go to the two common terminals 2 and 5

Horstmann 1 'Hot water off'' goes to...... Heatlink 'Hot Water Satisfied' 4

Horstmann 2 NOT USED

Horstmann 3 'Hot water on' goes to......Heatlink 'Hot Water Call for Heat' 6

Horstmann 4 'Heating on' goes to......Heatlink 'Heating Call for Heat' 3

The Nest thermostat can either be wired to T1 and T2 of the Heatlink for its 12v supply, or powered by a separate plug in power supply.

You don't mention any existing room thermostat, but if you have one, that will need to be removed from the existing system wiring, and the live switching wires that went to it need joining together at a convenient point. It can't just be disconnected, otherwise the wiring to the heating will be permanently 'open circuit' and the heating won't operate.