Nest 3rd gen install issue

28 Jan 2017
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United Kingdom
Hi, I'm looking for some advise. I have installed a nest heatlink. when i use the wirelessly connected nest thermostat to control my heating it won't switch the heating on, it will if i select boost on hot water switch the hot water on. to complicate things (with makes me believe it is wired up correctly, mostly) when i push the large button on the front of the heat link it switches the heating on! it just won't do the heating through the thermostat or iPhone app. Who i do try to switch the heating on through the app i hear the heat link click and the valve turn in the boiler also the old existing thermostat in the hall clicks (which i have turned on to max) but the pump DOES NOT fire up with the boiler. again when i hit the hot water boost in the app everything clicks and the boiler fires up.

Any help would be greatly appreciated. thanks


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Bit more info ports 3 and 4 in the Towerchron QE2 are the water and CH calls to heat. the grey and blue are going to the nests 3 and 6. The live in the nest is linked through to 2 and 5. the remaining wiring in the towerchron has not been changed other then me pinching of the live and neutral for the power link. if i remove all of the nest wiring out of the towerchron and put the original timer back on everything works as it should. thanks
Thanks to Mark C off another forum for the solution everything now works perfectly. solution:

So, all you had to do was jumper 3 (CH ON) to 4, connect live to 6 and have (HW ON) fed off 5.
Turn on CH it also passes current to 4/5 which is "Normally ON" so kicks in the HW. Turn on "JUST" HW it bridges just 5 & 6 (4 & 5 are no longer bridged so no current to CH) Simples :)
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Agreed! Nest will no doubt want to be considered cutting edge and are probably in denial of the existence of gravity hot water systems, or think them too old to consider. Plus they are an American company and I imagine gravity systems are possibly a bit of a UK thing.
The reality is that you could have achieved a better energy saving if you had the gravity converted to fully pumped instead of the Nest.

Gravity is a very old system and most inefficient as it requires the boiler to be on for a very long time while the water is being heated.


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