Nest installation question - wiring

[Amit Gohil]

Hi All,

First of all, thanks to all who can assist in my project of replacing current controller/thermostat with Nest.

To set the scene
- New build house which has an Ideal Logic Heat H24 Boiler (OpenTherm compliant)
- Danfoss FP715 controller at the boiler
- Wired Thermostat in the hall way
- Wireless Danfoss thermostat on the second floor master bedroom
- Megaflo tank in airing cupboard

I think i understand what i need to do, however, i wanted to clarify before i run in to trouble

Wiring at the controller (As is)
L - Live - 3 wires (3 brown)
N - Neutral - 3 wires (2 blue and 1 grey)
1 - DHW Off - No wires
2 - HTG Off - No wires
3 - DHW On - 1 Black wire
4 - DHTG On - 1 Brown wire
5 - Remote sensor - 1 wire (blue)
6 - Remote sensor - 1 wire (brown)

Assumptions
- 5 and 6 - are the 2 wires that go to the thermostat in the hallway.
- L - has 1 wire from boiler, 1 from fused main, 1 from upstairs Megaflo?
- Wires (Grey and black) combine in terminal block

Wiring at the Nest Link (To Be)
L - Live - All Live wires
N - Neutral - All Neutral wires
1- DHW Off - Nothing
2- HTG Off - Nothing
3 - DHW On - Nothing
4 - DHTG On - Nothing
5 - Remote sensor - 1 wire (blue)
6 - Remote sensor - 1 wire (brown)
OT1 - OpenTherm wire 1 - Black wire from old connection 3
OT2 - OpenTherm wire 2 - Brown wire from old connection 4
Earth - for T1 and T2 (If used) - Add a earth cable and wire to back box
T1 - 12V DC Power - Wire from connection 5
T2 - 12V DC Power - Wire from connection 6


I have attached a image of the current wires, sorry if it not too clear but i have tried to provide as much information as possible. Going of the manuals, since the system is OpenTherm i have assumed since i only have 2 possible wires (Negating Live, Neutral and Thermo stat) that i need to wire in to the OT1 and OT2 connections on the Nest.

Also, i guess the wireless thermostat i have on the second floor would need to be replaced with another nest thermostat and becomes redundant.

Thanks in advance again to anyone that can help.

Much appreciated.

Bob.

 

[Amit Gohil]

ok guys....so have done more reading...

Looks like i connect as below....

L - Live - All Live wires
N - Neutral - All Neutral wires
1- Satisfied (Heating) - Nothing
2- Common (Heating) - Loop Live to here
3 - Call for Heat (Heating) - Wire from old connection 4
4 - Satisfied (Hot Water) - Nothing
5 - Common - (Hot Water) - Loop Live to here
6 - Call for Heat - (Hot Water) - Wire from old connection 3
OT1 - OpenTherm wire 1 - Nothing
OT2 - OpenTherm wire 2 - Nothing
Earth - for T1 and T2 (If used) - Add a earth cable and wire to back box
T1 - 12V DC Power - Wire from connection 5
T2 - 12V DC Power - Wire from connection 6

Hopefully someone is able to confirm..thanks all.

 

[shambolic]

Be very very careful what you are doing as a lot of new build fitting logics have outside temp sensors and HW off from cyl stat needs to be wired to boiler switch live 2.
If you are removing the boiler cover to alter wires you need to take a gas rate, an inlet pressure, test FSD and carry out a high and low flue performance test.

 

[Amit Gohil]

I don't believe there is an outside temp sensor. Not one which I was made aware about. Is there anything I can check or take photos off that could clarify?

Otherwise, is the wiring suggested above sound correct?

 

[D_Hailsham]

Why are there two thermostats?
Is the house zoned?
If so, you need two nests, one for each zone. (See the Tip on page 10.)

Why no connections to OT1 and OT2? Have you decided not to use Opentherm?

 

[Amit Gohil]

Why are there two thermostats?
Is the house zoned?
If so, you need two nests, one for each zone. (See the Tip on page 10.)

Why no connections to OT1 and OT2? Have you decided not to use Opentherm?

Hi. Thanks for your reply.

Yes the house has additional zone and thought as much that I would need a second nest.

Ot1 and ot2 - I don't know whether just putting wires in to ot1 and ot2 from the 2 existing wires (heating / water - connection 3 and 4 from danfoss ) will just work. I assume the wiring would have been more specific to be able to use ot1 and ot2? Or are you asking because I can just connect existing wires in to ot1 and ot2 since I have a opentherm compliant boiler?

Thanks.

 

[Amit Gohil]

Why are there two thermostats?
Is the house zoned?
If so, you need two nests, one for each zone. (See the Tip on page 10.)

Why no connections to OT1 and OT2? Have you decided not to use Opentherm?

Which tip are you referring too? Is it a different post?

 

[D_Hailsham]

Which tip are you referring too? Is it a different post?

Page 10 of the Nest Installation instructions.

Opentherm cannot be used if you have more than one zone as they could be asking for different flow temperatures from the same boiler!

 

[Amit Gohil]

Page 10 of the Nest Installation instructions.

Opentherm cannot be used if you have more than one zone as they could be asking for different flow temperatures from the same boiler!

I guess that clears it then. Will connect to 6 and 3. And link live in to 2 and 5.

I think the second thermostat is wirelessly connected to the original controller so don't know (battery power) so don't know whether it is a true 2 zone? Not sure how to check.

 

[sparkymark75]

Be very very careful what you are doing as a lot of new build fitting logics have outside temp sensors and HW off from cyl stat needs to be wired to boiler switch live 2.
If you are removing the boiler cover to alter wires you need to take a gas rate, an inlet pressure, test FSD and carry out a high and low flue performance test.

@shambolic Would an outside temp sensor in an existing central heating setup be an issue for an installation of Nest?

 

[Dan Robinson]

It shouldn't, but it could.

You'd have to talk to Nest.

But heed Shambo's second sentence....This dude knows where he's at with Logics.

 

[sparkymark75]

It shouldn't, but it could.

You'd have to talk to Nest.

But heed Shambo's second sentence....This dude knows where he's at with Logics.

My Ideal boiler wiring all runs to a junction box so I don't go near the boiler itself. I also don't have a water tank which also simplifies things.

 

[Dan Robinson]

Edit.


Just realised there were 2 Op's.

The very reason why post hijacking is frowned upon.

 

[DP]

I suppose everyone reading or responding has his/ her own take on what it is all about
Proffesionals have responded to this often asked query, two of whom have immense knowledge of the subject, one who perhaps knows more about ideal boilers than collective knowledge about that appliance among a group of part changer calling themselves heating engineers.

DH. If the boiler was running on low burn for CH and HW, HW demand would never be satisfied. Think about it. Hence what Shambolic wrote. It is stuff like this, casual Nest/ hive installer may not be aware of as one needs to have better understanding of the appliance

 

[Dan Robinson]

My Ideal boiler wiring all runs to a junction box so I don't go near the boiler itself. I also don't have a water tank which also simplifies things.

Start your own thread.