I really need help with replacing this current danfoss thermostat with a new nest thermostat e heat hub. I'm in the UK.
Below is the new heatlink just need to know what wires I need to wire and what ones I need to isolate.
Thermostat Wiring – Replacing Old Danfoss with Nest Thermostat E Heat Link
central-heatingdiy-vs-prothermostatthermostat-c-wirewiring
Related Solutions
This has been idle a while, but my guess is you need to connect the Nest to the R terminal of thermostat 1 on the controller instead of R1.
It looks like your control system was designed and wired for a heatpump but you no longer have one (there are only 4 wires on the lower left block which I think is the output to the furnace/AC compressor). If so the O and B wires are unneeded and can be removed from the control panel.
So what I would try:
- Zone 1 R to Nest Rh (24VAC Hot)
- Zone 1 C to Nest C (24VAC Common)
- Zone 1 W to Nest W1 (Heat)
- Zone 1 Y to Nest Y1 (Cool)
- Zone 1 G to Nest G (Fan)
Only thing I don't understand is how the fan gets turned on by the second thermostat in Cool mode. (In cool usually the thermostat has to tie both G and Y to R (24VAC Hot), in heat only W has to be tied to R (+24VAC Hot)... Since it works it must be something the controller does automatically.
By connecting the Nest to the C terminal it gets access to 24VAC without trying to power it self from "leakage current".
It you want to test, jumper Zone 1 R to Y for a minute and see what happens. Does the compressor come on outside? Does the interior blower fan?
Double check this against the manuals..
I fixed it myself. In the manual (page 18) there is the following image.
As shown on the photo in the question:
From left to right: The red "bridge cable" is meant to close the circuit in order for the next two (bus +/-) to work. But the bus connectors only work with with an eBus system. Which is not compatible with the Nest Heatlink.
The two wires that are used to connect the boiler to the heat link (the left brown/blue wires) should be connected to the 4/3 connectors instead. So after removing the red bridge cable and connecting the heat link to 4/3 of the boiler, it worked fine.
Disclaimer for those with the same problem: I'm not a electrician, although I did check the solution with one. Try this at your own risk.
Best Answer
If this is the Nest E UK thermostat (the same designation is used for completely different products in the USA. Nest's own documentation is not always clear which product is being referred to.)
On the Nest, there are terminals for Common, NO (normally open) and NC (normally closed). In addition to these terminals you can also see the OT1 and OT2 terminals, which are used for OpenTherm.
Ignore OT1 and OT2.
Connect Danfoss L Brown to Nest Common
Danfoss 3 ON (black?) Sleeved Brown to Nest NO.
Make sure that Neutral (Grey sleeved blue) and Earth (green/yellow sleeve) are tidied out of the way and cannot connect to anything.