Installing nest thermostat

[Nickclarke2183]

So after reading online and being led to believe this was simple, I'm stuck.

I originally had a potterton controller ep2002. Wired as follows...

Screenshot_20190925_184429_com.android.gallery3d

• Nickclarke2183
• 25 Sep 2019

IMG_20190925_184354

• Nickclarke2183
• 25 Sep 2019

Not that terminals L and 5 are linked.

I hkave rewired as follows and the nest unit is on but the boiler is not. Not sure what I have done wrong.

IMG_20190925_184405

• Nickclarke2183
• 25 Sep 2019

IMG_20190925_184419

• Nickclarke2183
• 25 Sep 2019

Can anyone help?

 

[ericmark]

N = Black = Neutral N on Nest
L = Red + Red link = Line = L on Nest
1 = Blue = HW off = 4 on Nest
3 = Yellow = HW on = 6 on Nest
4 = Red = CH on = 3 on Nest
5 = Red Link = CH Com Line = 2 on Nest
Note Nest also needs Line to 5 as not internally linked. And T1 and T2 need to go to thermostat unless supplied else where.
So needs two wires in L and two wires in 2 so L, 2, and 5 are all linked, I have problems getting two wires in the hole so put a wiring centre next to the Nest heat link.
So should see:-
Black = N
Red = L
Link = 2 Commom
Red = 3 CH on
Blue = 4 Satisfied NC DHW
Link = 5 Common
Yellow = 6 Call for DHW
But you show:-
Black
Red
Yellow
Red
Brown
Blue
Empty
Clearly it will not work without link, but Nest has 1, 2, 3 CH and 4,5,6 HW but the old one has 1 HW, 2 CH, 3 HW, 4 CH, 5 CH.

Sorry late at night original post got CH and DHW swapped, the wire on satisfied DHW points to no tank thermostat either Y Plan or C Plan without motorised valve.

 

[Nickclarke2183]

Hi, thanks for the reply but I don't think your numbering is correct either.

123 is heat 456 is hot water. Your reply has 123 as hw, 456 as ch.

Are you able to update your reply?

Many thanks.

 

[muggles]

@stem will sort you out!

 

[stem]

It’s just a matter of moving the from the EP terminals to the Nest terminals that have exactly the same function. Their functions are shown in the diagrams you have posted, so based on them:

NEST HEATLINK

Black wire in EP N ..... Nest N

Red wire in EP L ..... Nest L (for now discard the link to EP5 we’ll come back to the links later)

Blue wire EP 1 Hot water off.....Nest 4 Hot water satisfied

Yellow wire in EP 3 Hot water on.....Nest 6 Hot water call for heat

Red wire in EP 4 Central Heating on... Nest 3 Heating call for heat

Then add links so that Nest terminals L, 2 and 5 are electrically connected together.

It would appear (can’t see it clearly) that as well as the loop, there may also be a brown wire in terminal 5, that will also need to be connected to the L (connect it to terminals L, 2 or 5 whichever is easiest)


NEST THERMOSTAT

You can power the Nest thermostat by wiring it to Heat link terminals T1& T2, or by using a separate plug in power supply. If you do use T1 & T2 to power it, the Heat link earth connection is also required.


EXISTING ROOM THERMOSTAT

If you don't have an existing room thermostat, then that's it, job done.

If you do have an existing room thermostat that will need decommissioning properly, it can't just be disconnected and removed or the central heating will be left 'open circuit' and will not work. This is done by connecting the live thermostat switching wires together at the thermostat, or at their place of origin. Or alternatively leave it in place and set it to its maximum setting. That way it won't interfere with the Nest.

 

[Nickclarke2183]

Thanks so much. I will give this a try tonight

 

[Nickclarke2183]

Unfortunately that didn't work.

Boiler had power but when you turn up the nest thermostat the boiler turns off.... No heat.

Swapped terminals 1 and 3.

Boiler has power. Turn up the thermostat and you hear the switch but no heat.

I'm at a loss. Time to call someone in?

 

[ericmark]

Swapped terminals 1 and 3.

Where does either mine or Stems post say use terminal 1? There should be nothing in terminal 1, come on you noted my error, I am sure you can work it out once it has been pointed out there are three terminals connected to line.

 

[CBW]

How's it wired now after Stems advice? Photo?

 

[CBW]

Where does either mine or Stems post say use terminal 1? There should be nothing in terminal 1, come on you noted my error, I am sure you can work it out once it has been pointed out there are three terminals connected to line.

So is common basically a live supply? Is this true in all heating situations?

 

[muggles]

So is common basically a live supply? Is this true in all heating situations?

Sort of. Common is the supply side of the switch, which may or may not be 230v depending on the appliance and accessories installed. Nest isn't internally linked between L, 2, & 5, because in some installations you might have 12v or 24v going into 2 & 5 instead.

 

[ericmark]

Likely you have Y Plan as connection to DHW off, but with the C Plan if there is no tank thermostat then the N/O and N/C are feed into relay and Com is feed out, the Nest is one of the few programmers that allow one to wire it that way around, and also allow both 24 volt and 230 volt control circuits plus if required OpenTherm it also allows both hard wiring to remote thermostat or wireless, it will work with nearly every low current control system you can think of, the draw back is the terminals are small and there are no internal links, the user has to hard wire the links.

In your case control is 230 volt, so there needs to be links between Line and the two com terminals.

Both Neutral and Line are considered as Live, so we call the phase wire Line, I think most DIY people consider it as Live and they do not consider Neutral as Live but technically should call it Line not Live, sorry if this has caused any confusion it was not my intention.

Also sorry for my earlier error getting DHW and CH swapped around I have corrected my error.

 

[CBW]

Both Neutral and Line are considered as Live, so we call the phase wire Line, I think most DIY people consider it as Live and they do not consider Neutral as Live but technically should call it Line not Live, sorry if this has caused any confusion it was not my intention.

I don't get why Neutral is considered live? I thought it was usually connected to earth at some point?

 

[stem]

Was it all working OK before the EP was removed?

At the end of the day terminal 4 from the EP becomes live when it the EP switches the heating on, terminal 3 of the nest does exactly the same thing. Have you checked that the red wires that were in the EP L and 4 are connected as below and not the other way around? Is terminal 2 connected to L?

The red wire from EP L ..... goes to Nest L

The red wire in EP 4 Central Heating on... goes to Nest 3 Heating call for heat

Was / is there an existing room thermostat, and if so what have you done to / with it?

Did anything happen during the fitting of the Nest when you were had the wires connected wrongly, fuse blown for example?

Can you explain what you mean by the following please?

Boiler had power but when you turn up the nest thermostat the boiler turns off.... No heat.

Are you saying that the boiler is running (ie firing) and when you turn the nest up the boiler stops firing? Is it possible that the boiler has shut down because of its internal thermostat, because there is little demand for heat (TRV's closed for example)

Is the hot water working OK with the Nest?

Have you checked that every wire has been moved as I described and all of the links are present, it's easy to miss one

Have you checked every terminal to make sure that the connections are secure and the conductors are clamped under the terminals not the insulation? Nests are fiddly beasts for those of us that are used to them. Bad connections are common.

Because you had a wire connected to terminal 1 of the EP, we have all assumed that you have a system with a 3-port motorised valve (aka Y-Plan) is that correct?

As @The Novice asks, a photo might help.

 

[ericmark]

I don't get why Neutral is considered live? I thought it was usually connected to earth at some point?

With a TT earthing system the neutral and earth can deviate by 50 volt, also although one should never borrow an neutral it does happen so the IET/BSi regulations say that neutral and phase all classed as Live, yes it's permitted with some types of supply to just switch the Line, but since you don't know type of supply an isolator always switches both line and neutral, i.e. all Live wires.

I found when fitting my Nest the terminals are rather small, getting two wires in one terminal is not easy, so I fitted a wiring centre (Junction box) below my Nest to give more room to join wires so only one wire in each Nest terminal, I also filed the plastic under the terminals to give maximum room, and still tight getting 10 wires in, very easy to not get a wire in the hole and tightened up fully even with only one wire.