Prime Day on July 11th saw a big drop in the price of a Nest v3 system to £135. I’d been thinking of getting one for a while, so this discount was too good to refuse – especially as I’d received a £20 Amazon voucher from work, so it ended up being £115 of my own money.

It arrived yesterday.  I had a quick look over the instructions that evening and searched Google for help setting it up for my boiler, but I didn’t find anything helpful.  I know they say it’s meant to be installed by a pro, but from reading it seemed it was quite simple once you understood what activates what on the boiler.  It took me a while to get that understanding – but once I’d looked at the back of the existing programmer that’s built in to the heating system it fell into place.

Given I’ve worked it out and successfully installed it I thought I’d share what I did for anybody else who struggles to find the help they need.

My existing system is an Ideal iStor HE260 and HE325 system boiler, and it turns out installation is pretty simple, particularly in my case as I’m using the Nest thermostat on a stand, rather than replacing my existing thermostat in the hall.

This wiring diagram from the manual shows how the thing puts power to the boiler, which is essentially what the heat link will do; it’s a glorified power switch:

The Link on the right brings in the mains to the Programmer.  The programmer then provides the power to the Central Heating and Hot Water as it’s a switch that activates according to the programmed schedule.

Remove the link and the programmer has no power to provide, instead your wire the Heat Link to the CH and DHW terminals so it controls the power provided.

As mentioned, I didn’t remove my old thermostat from the equation, so the caveat above is that the Central Heating power can still be interupted by the old thermostat breaking the circuit.  In my case I’ve just turned the thermostat to maximum, so it will never break the circuit.  The alternative is joining the wires that go to the thermostat, but it’s a bit awkward to get to so I didn’t bother; leaving it as is also makes it simpler to reverse the installation in future.

Tools for the job

Make sure you’ve got everything ready… you’ll need some additional 2-core cable as that isn’t supplied with the Nest system.

Installation Steps

  1. Switch off the mains fuse for the boiler and switch it off at the wall too, just to be sure!
  2. Take the cover off the heat link.  Using a pencil mark where you need to drill screw holes on your wall where you’ll be attaching the Heat Link.
  3. Drill the holes using a 55mm or 60mm drill bit and insert your rawlplugs.
  4. Fully-loosen the screws inside the Heat Link on the following junctions:
    – N (neutral)
    – L (live)
    – 2 (Common – the live in to Heat Link to control Central Heating)
    – 3 (Call-for-heat – the live out from Heat Link to your Central heating)
    – 5 (Common – the life in to Heat Link to control Hot Water)
    – 6 (Call-for-heat – the live out form Heat Link to your Hot Water)
  5. Connect the neutral terminal and live terminals on  the Heat Link.  Neutral goes to “N” while live goes to “L”, “2” and “5”.
  6. Connect the output terminals “3” and “6”.  I bought 10m of 2-core cable so used the same one.  Remember which you’ve wired to where, and it’s a good idea to label these at the other end as Live, given the blue isn’t neutral as it might be expected.  I used blue for the Hot Water here, because blue = water, so easy to remember.  I didn’t trim the cable at this point, so as to ensure there was enough to threat it into the boiler as required.
  7. Attach the heatlink to the wall.
  8. Wire the Neutral and Live cable from the Heat Link into your mains switch (also shown above).
  9. Open the top section of your boiler by removing the top two screws at the front on the left and right.  Lift it off.
  10. Unclip the bottom section of the boiler.  Unscrew the screw at the bottom of the plastic control panel, then push the panel up to unclip it and remove it.  (not shown here, as the screw wasn’t attached to mine so it just unclipped).
  11. It’s not necessary, but it simplifies the next bit of wiring if you unclip the plastic wiring clip that connects the panel to the boiler.
  12. Remove the loop wire (the red wire below) from the input terminals.  This was what took the mains feed into the built-in programmer.
  13. Now connect the Central Heating and Hot Water live feeds from your Heat Link; in my case blue was Hot Water, brown was Central Heating.  I’d threaded the cable into the boiler so cut the cable to an appropriate length as I did this.
  14. Reconnect the panel to the boiler wiring clip, then slot the panel back into place.
  15. Reattach the boiler panels.
  16. Attach the front panel to the Heat Link.
  17. Turn the boiler socket on, then flip your mains fusebox switch to power up the boiler.
  18. The Heat Link should power on.  Push the central button to “boost” both Central Heating and Hot Water to confirm it works.
  19. Now set up your Nest thermostat following the instructions on screen.