Google Nest can’t connect to Heat Link – ‘failed to connect to Heat link’

The Google Nest thermostat dial can have a wired connection and/or a wireless connection with the Heat Link base. A loss of wireless connection is a rare event and it usually fixes itself. In my experience a power cycle or a wait or at most a soft restart (press for 10 seconds) puts things right.

But should you do something like swop in with new unit, or do a ‘hard reset’ because you’ve bought a s/h one or you think a ‘hard reset’ will freshen it up, you will need to pair one with the other. A few forum posts, suggest that re-pairing is sometimes tricky – and it presents as error h71.

Background: Using Nest is not only good for conserving fuel it’s intuitive and full of features. The Google Nest thermostat 2nd & 3rd gen consist of a ‘Heat Link’ which connects to the boiler or aircon. In addition a most excellently designed thermostat dial sits in the room measuring the temperature and tells the Heat Link to turn the heating or aircon on or off. (There are many versions of Google Nest – some don’t use a Heat Link; some are low voltage, some use mains – so you ought not expect to mix and match parts or import them).

The Thermostat menu (eg under Equipment) will have a HEAT LINK option which tell you if the current connection is wired or wireless or both. The 3rd gen Heat Link can connect directly to the Thermostat with a 2-core flex that carries 12v on connectors T1 and T2. This connection is optional because the Thermostat is wireless and can be placed anywhere in the home as long as it’s powered by a USB lead and charger.

Nest Heat Link pairing tips

Put aside any desperation to pair the Heat Link to the Next thermostat in order to keep warm. The central override button on the Heat link can turn your heating on and off. The thermostat can always control the Heat link when they are physically wired together (run a twin-core flex between T1 and T2 terminals on each device).

The Heat Link has a fixed, unique six digit code which is printed under its plastic cover (aka Entry code; Heat link code). The code is also printed on the plastic cover near the cover retaining screw. These codes will be identical – unless like me you had muddled up two kits. The code must be the same code as the code shown by the dial thermostat under eg Technical info > Heat link. If not, at the appropriate time during setup or pairing you’ll be able to ‘REPLACE HEATLINK’ and enter the code that you have.

to reset the Nest thermostat (aim not to!)

You can do a restart, or shall we say ‘soft reset’ on the Thermostat if you press the dial down for 10 seconds. However there’s a ‘harder’ reset and you’ll know if you’ve done a hard reset because the thermostat starts up asking you what language you use and what wifi SSID you have. To ‘hard reset’ the Thermostat you need to be able to reach its RESET menu. Resetting everything requires that you re-pair the devices so it’s wise to reset just some of the settings. A hard reset of the Thermostat may occur when the dial is removed from its base and then long-pressed. The thermostat will want to be USB powered while you’re doing that.

to reset the Heat Link (aim not to!)

A green light means the Heat Link is paired. A yellow light means the Thermostat is out of range or starting up or having problems – but the yellow light means it’s at least paired. To reset the Heat Link (while powered) press and hold the centre button for about 10 seconds; wait for the light to change or flash blue before you release.

To do a harder reset on the Heat Link (while powered) press and hold the centre button; notice the light change or flash and continue holding until this happens again – about 45 seconds overall. When you release a blinking blue light means the Heat Link is waiting to pair. This is the best moment to get the thermostat looking to pair with the Heat Link.

to pair the Heat Link with the dial thermostat

the Thermostat will tell you that it needs to pair wirelessly with a Heat Link, or it’ll refer to error h71 or you’ll see messages to the tune of ‘can’t control this equipment’. I’ve always found this message to be more alarming than is the situation. Try this: press the Heat Link button for 10 seconds and/or press the Thermostat screen for 10 seconds.

When pairing fails it helps to recall your experience pairing the more tricky Bluetooth devices:

• at the moment of pairing the Thermostat to the Heat Link either turn off everything with a radio signal (BT; wifi; phones) or somehow move away from interference. This was a key factor for me in my house of gadgets.
• at the moment of pairing the Thermostat to the Heat Link place the Thermostat actually on the Heat Link. This worked for me.
• I had pairing success when the Heat Link and Thermostat dial were temporarily wired together ie run a twin-core flex between T1 and T2 terminals on each device.
• if pairing fails check in the Thermostat menu (eg TECHNICAL / EQUIPMENT) to see that it has the correct Heat link code/Entry code. If you need to change the code shown in the Thermostat first reset the Heat Link and only enter the code as the Heat Link starts its flashing blue pairing LED.

the drastic Heat Link pairing process

1. if my bullet points above fail you do a hard/full reset: remove the thermostat from its base; press the screen holding the back for 10 seconds. As the thermostat restarts reset the Heat Link.
2. you’ll be asked to put the thermostat back on the base and enter details. As you have hard reset the Thermostat do check its menu holds the Heat link code that you’re pairing it to.
3. restart the Heat Link (eg long press for 40 seconds) to get to the blinking blue LED – then at that point get the thermostat looking for it.