Nest Thermostat Y-Plan Install

[jay83]

Hi,

I've recently bought a Nest 3rd Gen Thermostat and I'm looking to install it myself. I know how the system works but I'm unsure about a few things.

Currently, I've got an Ideal Classic Boiler and Danfoss FP7801/FP715si Programmer on a 3A spur in the Kitchen, Danfoss RMT230 in the Hallway, Danfoss WC4B Wiring Centre in the Airing Cupboard with Cylinder and 3 Port Valve.

I'm wanting to blank off the old Programmer in the Kitchen using connector blocks and blanking plate. Install Heat Link in Airing Cupboard next to Wiring Centre using 3-core cable for Live/Neutral/Earth and 4-core for HW ON/HW OFF/HTG ON and install Thermostat in Hallway using 2 wires of existing Thermostat.

Am I right in thinking I can -

Use 3A connector blocks for terminating wires (Live/Neutral/HW ON/HW OFF/HTG ON) from old Programmer (keeping existing wiring arrangement the same) in the Kitchen and then put blanking plate over?

Use 0.75mm 3-core 3A flex for Live/Neutral/Earth from Wiring Centre to Heat Link using Live/Neutral/Earth terminals in Wiring Centre?

Use 3A connector blocks to terminate redundant wires from HW ON/HW OFF/HTG ON from Wiring Centre?

Use 0.75mm 4-core 3A flex for HW ON/HW OFF/HTG ON from Wiring Centre to Heat Link?

Use 3A connector blocks to terminate redundant wires (Neutral/Earth) from Thermostat and Wiring Centre?

Use 3A connector blocks to extend 2 disconnected wires of current Thermostat from Wiring Centre to Heat Link?

 

[stem]

You have provided the information that you need. But I think you are making it more complicated than you need to. The wires now going to the existing programmer are connected as per the diagram you posted as below....

All of the wires presently connected to the programmer are simply moved to the Nest Heat link terminals that have exactly the same functions. So...

Wires in N = Heat link N
Wires in L = Heat link L
Wire in DHW OFF 1 = Heat link 4 Hot Water Satisfied
Wire in DHW ON 3 = Heat link 6 Hot Water Call-for-Heat
Wire in HTG ON 4 = Heat link 3 Heating Call-for-Heat

Links are then required between Heat link (L) and the two 'Common' terminals (2) and (5) so that the 3 terminals are electrically connected.

The old thermostat needs to be decommissioned. It can't just be disconnected, otherwise the heating wiring would be left 'open circuit' and would not operate. This is done by tracing the old thermostat cable back to its origin. The live thermostat wires should go to terminals 2 & 3 as below, but please check that they do....

.....if they do, disconnect all of the wires from the existing thermostat and remove the old thermostat cable from the wiring centre. Then insert a link to join together the two terminals 2 & 3 where you have just removed the two live thermostat wires from.

The Nest thermostat can be powered using a separate plug in power supply, or by running a new wires to connect the Thermostats T1 & T2 terminals to the same terminals at the Heat link. If you do the latter, an earth connection to the Heat link earth terminal is also required.

 

[jay83]

Thanks for replying so quickly.

I'm wanting to install Nest Thermostat in Hallway where existing Thermostat is, which is directly above wiring centre as running a new cable from Kitchen to Hallway would be a lot of work and there's no sockets near existing Thermostat.

If installing Heat Link in the Airing Cupboard, would the Live/Neutral/Earth terminals in Wiring Centre be OK to use to power Heat Link through 3A cable or would the cable need to be 10A?

 

[stem]

The Nest thermostat is not 230V. It requires either a USB or 12v connection for power, so I assume you will be using a USB adapter, or rerouting the existing thermostat cable to the Heat link 12v terminals.

The whole heating system installation should be fed via a 'fused connection unit' fitted with a 3A fuse, so you won't need cable rated at 10A. Which wouldn't fit into the Heat link terminals anyway.

 

[ericmark]

Personally I would put the heat link above the wiring centre, as you don't need access to it, and you should have all the wires you need. To work out what does what the colours of the motorised valve is your friend, as they are fixed by valve manufacturer so reasonable guaranteed to be correct.

A quick check it seems the wiring centre is wired as on the lid, so it would seem remove link 2 to 4 and move link from 3 into 4 that will mean thermostat now shorted out. And the thermostat wires 2 and 3 are free for you to use to power the new thermostat from T1 and T2 on heat link, however I would use meter to ensure they are dead before reusing. At this point heating should still work, but thermostat will do nothing.

You need 7 wires to heat link, however I would keep the T1 and T2 in a different cable to rest.
So remaining 5 are.
Neutral that is on vertical strip.
Line should be 11. also on the heat link 2 and 5 need connecting to line, since the terminal holes in heat link are so small, may be easier to take three line wires from 11, 12, 13 which are all line on wiring centre to L, 2 and 5 on heat link.
8 on wiring centre to 4 on heat link (DHW satisfied)
9 on wiring centre to 6 on heat link (call for DHW)
10 on wiring centre to 3 on heat link (call for CH)

8,9,and 10 brown, black and grey one would assume goes to original programmer, however it will also need a line and neutral to original programmer from pictures I can't work out which wires they are, maybe the programmer feeds the wiring centre? and you will need a junction box of some sort where the programmer was?

In my house there is a blanking plate where programmer was covering the connection block where in my case the T1 and T2 wires are connected, you may need to do similar but in your case L N E?

Pobody's Nerfect I may have made a mistake, it is up to you to check I have got it right. You need to find the thermostat neutral (seems likely grey is neutral) and remove it, I can't see where the wire goes, and it seems looking at pictures you need a conduit box gasket and lid to replace old programmer, it looks like a conduit box?

 

[jay83]

I managed to get more pictures of current wiring last night.

The Wiring Centre certainly seems wired as on lid.

It looks like Thermostat is a straight 4 core cable with Neutral and Earth into Wiring Centre Neutral and Earth terminals.

 

[stem]

The Wiring Centre certainly seems wired as on lid.

OK that's a good start.

It looks like Thermostat is a straight 4 core cable with Neutral and Earth into Wiring Centre Neutral and Earth terminals.

So to decommission it:

Disconnect all four cores and remove the thermostat cable, so that it is safely out of the way. The back and brown wires marked with X below should have gone.

Remove the loop between 2 & 4,

Move the top red wire currently in 3 to 4 where it will now be connected to the brown/white wire (that goes to the motorised valve) that is already there. [This is instead of the link I mentioned originally, but electrically achieves the same thing]

When you have removed the old thermostat from the other end of it, the cable should not be connected to anything. Ideally you should check it with a multimeter to be sure, [I once found someone had connected a wall light in an adjacent room to a thermostat cable by tapping into the L & N wires halfway along ] If you wish you can then use two cores of this cable to connect the Heat link T1 and T2 to the Nest thermostat T1 & T2.

The Brown to Black in connector block behind Programmer, is that for Switch Live to Wiring Centre terminal 12?

Your guess is as good as ours, and probably better as you are actually present. Unfortunately there is no fixed or set way to wire a heating system. I have seen 100's and no two are exactly the same. The way wires are joined, the cables chosen and the wire colours used is solely at the discretion of the original installer and the layout of the various heating components in relation to each other inside your home. Photographs of the wires don't help unless you can tell us what is connected to the other end of each wire and any other wires that terminate from it.

It's a bit like me posting this....

....and without giving any other information asking where each of the roads goes to and from, and assuming that every road junction is exactly the same as those in another part of the country.

Sometimes we can take an educated guess and then confirm our suspicions by electrical testing to make sure, but not over a forum. For DIY installation the simplest way would be to swap the existing programmer for the Heat link, and decommission the existing thermostat. The wires can be extended or shortened if required. Otherwise you will need to engage the services of someone competent that understands how all of the system components work and interconnect in relation to each other.

 

[jay83]

Hi Stem,

Thank you for all your replies, I've taken your advice onboard and I'm going to fit the Heat Link where the existing Programmer is and have the Nest Thermostat on a stand via USB.

My question is, after checking the fused spur which is next to the Programmer feeding that, the boiler and the wiring centre in the airing cupboard, it has a 13a fuse fitted (not by me probably by a previous owner) shouldn't this be 3a as specified in the Ideal Classic SE 9 FF boiler manual or is it fine to leave the 13a fuse in?

I don't want to power the heating system back up to find that the Heat Link has blown which is also rated at 3a.

Cheers

 

[EFLImpudence]

Just fit a 3A fuse.

 

[stem]

Well done for spotting it. From experience, where boilers are fitted with a 13A fuse instead of a 3A, if a fault does occur it is far more likely to cause damage to the boiler or connected controls before the fuse blows.

Don't worry about it being insufficient. 3A is more than enough for the boiler and all of its ancillaries.

 

[winston1]

My question is, after checking the fused spur which is next to the Programmer feeding that, the boiler and the wiring centre in the airing cupboard, it has a 13a fuse fitted (not by me probably by a previous owner) shouldn't this be 3a as specified in the Ideal Classic SE 9 FF boiler manual or is it fine to leave the 13a fuse in?

When the same system is used in Europe it would be straight on to a 16 amp circuit without a fuse so theoretically 13amp is OK. That is why boilers are internally fused. Pity the people who write the manuals don't realise that. However if it makes you feel better fit a 3amp fuse. The fuse by the way is to protect the connecting cable not the boiler. Bet your cable is rated at more than 3 amps.

 

[stem]

Accessories such as programmers and thermostats which don't have internal fuses are also connected to the same FCU as the boiler.

I've exchanged many thermostats & programmers that have had their contacts welded together by a short circuit, and every time I have found that there has been a 13A fuse in the FCU. When a short circuit has occurred with a 3A fuse in circuit I've never known it happen.

A RGI I used to occasionally help out, once told me he couldn't sign off an installation unless the correct fuse was fitted. I don't know if that's still the case.

 

[EFLImpudence]

That implies that the programmer and thermostat companies make different products for the UK and Europe.

Do you think that is the case?

 

[winston1]

A RGI I used to occasionally help out, once told me he couldn't sign off an installation unless the correct fuse was fitted. I don't know if that's still the case.

The correct fuse is the one that protects the cable. With 1.5mm cable that would be 13a.

 

[winston1]

That implies that the programmer and thermostat companies make different products for the UK and Europe.

Do you think that is the case?

No I'm sure they don't.