NEST gen 3 fitting on Honeywell programmer and room stat

[Johnmdc]

Yes that looks right connection wise but still needs tidying up.
There is a circle of plastic on the back of the nest under the connections that you can knock out to bring the wires into it, so when you put the cover on you won't see any wires.

 

[EFLImpudence]

Note there was no brown in 1,

 

[JC-DIYman]

Sorry my mistake, will re set boiler and see if all works

 

[JC-DIYman]

Boiler does not ignite

 

[ban-all-sheds]

Sorry my mistake

Which?

Putting that brown into #1, or claiming that you hadn't, or not having any idea that you had?

 

[stem]

The yellow and red from the thermostat were connected to 2 and 3 which I removed and then removed link between 2 and 4. I then re-routed link from 9 to go to 4 instead of 3. I have photo of original layout if it helps.

That's OK, a bit of a complicated way of doing it, but it does reduce the number of links and electrically it works out the same as:

the white wire in the wiring centre terminal 4 will go to the motorised valve, and the yellow wire in wiring centre terminal 9 should be connected to the Nest Heatlink terminal 3 'heating call for heat'.

As there isn't a yellow wire at the Heatlink, there will likely be a change of cable somewhere along the route, but the end result should be that Heatlink 3 is connected to the motorised valves white wire.

 

[JC-DIYman]

Old programmer was a Invensys T45. Could the

That's OK, a bit of a complicated way of doing it, but it does reduce the number of links and electrically it works out the same as:


As there isn't a yellow wire at the Heatlink, there will likely be a change of cable somewhere along the route, but the end result should be that Heatlink 3 is connected to the motorised valves white wire

That's OK, a bit of a complicated way of doing it, but it does reduce the number of links and electrically it works out the same as:


The connection going into 4 on the heatlink is not the same colour as the one coming out on 8 on the wiring centre which is a red so somewhere there is a junction.

 

[JC-DIYman]

Which?

Putting that brown into #1, or claiming that you hadn't, or not having any idea that you had?

Brown was in 1

 

[Sam1008]

Sorry to bring up an old thread (and potentially hijack it) but i just used this along with Stems other posts to install a Nest v3 thermostat into my house. As with the OP, I have a 3 way port valve system and believed to have wire everything in as expected. The boiler is firing when CH or HW is requested however i realised this morning that when the CH only is requested when it turns off it leaves the port valve buzzing(?) like it still has power going to it. This doesn't happen with the HW and everything turns off and on as expected.

If i request both CH and HW together and turn them off together the valve doesn't make any noise making me think that it's something missing with the CH setup that is causing the issue.

I have disconnected the original thermostat which use to be in the hallway and removed the wiring from the junction box and connected the associated wiring together effective bypassing the old thermostat wiring.

Any help would be much appreciated, i feel like i'm 98% there and this is just the final point to finish off the install.

Thanks,
Sam

 

[stem]

If the hot water and heating are working properly, as they should be, then it will be wired up correctly.

The three port valve is a complicated beast, when not powered, it is held in the hot water only position by a spring. A motor then winds it to the mid position, and heating only position as required. When it gets to its chosen destination, the motor remains powered, but stalled to hold the valve in place against the force of the spring that is trying to pull it back.

However the main problem with the 3 port valve is, that when it has been moved from rest because the heating has been on, that even when the heating goes off, the valve will remain where it is with the motor permanently energised to hold it in that position. This is probably the buzzing you can hear.

If you were to turn off the mains supply to the heating system at the fused spur, the valve will then return to the hot water only position. After restoring power the valve will remain there until the heating comes on again. Probably best not to try this for a few minutes after the boiler has gone off in case a pump overrun is still operating.

 

[Sam1008]

Thanks for your quick response Stem. The information is extremely useful.

I have just done as you have instructed. Turn HW on, Turn HW off, check valve to confirm buzzing/engaged, turn off breaker, turn on breaker and check valve. As you suggested, the valve is no longer making any noise therefore it must have gone back to the default hot water only location.

All sounds good. My concern is that when the valve is left in the HW+CH or HW only position the valve gets hot (touchable but very warm). Is this safe?

 

[stem]

I guess it's safe, there must be millions of them out there all doing the same, and I can't think of one ever being blamed for starting a fire. But it will shorten the life of the motor, and it wastes energy. OK, I know they only use a few watts, but multiply that by the number out there and it all adds up.

In the winter, the heating is usually the last thing to go off, as the hot water cylinder is insulated, it will not need constant re-heating. Therefore, if the heating is the last thing to go off each evening the valve will remain powered all night.

In the summer when the heating is off and only hot water used, it's not a problem as the valve will not be energised at all.

 

[jimyol]

Hi Gary

The wiring at the programmer should be moved over to the Nest Heatlink as follows:

Honeywell 1 (Hot Water off).......Nest 4 (Hot Water Satisfied)
Honeywell 3 (Hot Water on).......Nest 6 (Hot Water Call for Heat)
Honeywell 4 (Heating on)..........Nest 3 (Heating Call for Heat)

The Lives / Neutrals are a like for like swap.

Then you need to add some links, so that the Live terminal also connects to the two common terminals 2 and 5

Which brings us to decommissioning the original thermostat. There are 3 possibilities. 1 is the preferred solution, but 3 is the easiest.

1. Find the opposite end of the thermostat cable to the thermostat, and disconnect it. Then link the terminals where the yellow and red wires came from together.

2. Remove the existing thermostat and replace it with a junction box, connect the yellow and red wires together and isolate / insulate the neutral

3. Leave the existing room thermostat in place and put the yellow wire in terminal 1 along with the red.

There are two choices to power the Nest thermostat, either wire it to the heatlink T1 & T2 which you can do using the existing cable if you have decommissioned the thermostat using method 1 above. Or by using a separate plug in power supply.

EDIT
Just to clarify. When you say:

"I want the nest stat to go where the original room stat is if possible using the power that is there to power it."

You can't actually do that. The existing thermostat wiring is 230V, but the Nest thermostat is only 12V. So, it needs to get that 12V from either a 'plug in' power supply, or by Wiring terminals T1 and T2 at the Nest thermostat to the corresponding terminals at the heatlink. As I said above, you can use the existing thermostat cable for the 12V, but only if it has been completely disconnected from the existing mains wiring. However, even if you do this, you may find that the cable doesn't run to where the heatlink is located. Depending on the wiring layout of your installation, you may find that the other end goes to a junction box / wiring centre elsewhere, making it impractical to use.

Hi all, I'm in the process of self-installing a Nest system, found this thread to be very helpful but sadly it's not working. I suspect that my problem might be due to the way I've decommissioned the existing thermostat - I used option 2 above. Previous wiring comprised of a blue incoming connected to N, a red incoming connected to L and a Yellow incoming connected to 3. The existing stat didn't have any terminals in positions 1 and 2. I've removed the stat and enclosed the wires in the existing backbox, with red and yellow joined together and blue safely terminated. Is this correct? Seems a lot easier than altering the wiring in the airing cupboard, but the system isn't working - new stat does not trigger CH, though I hear a clicking from the Heatlink when asking for heat.

 

[stem]

If your wiring followed the usual wiring colour format then normally:

Red = Live
Yellow = Switched Live
Blue = Neutral

In which case, linking the Red and Yellow as you have done would be correct.

There is a simple test you could try. Wire the original thermostat back in exactly as it was, and turn it to its maximum setting. Now try the Nest. If it works, then your decommissioning of the thermostat was wrong. If it doesn't work the fault is elsewhere.

 

[Taylortwocities]

@jimyol
I guess you still have the original programmer in play? If do you’ll need to set that to permanently on, or your hive won’t work when the heating time is off.
Your hive is best wired into the wiring centre, not after the existing programmer.