Nest Learning Thermostat 3rd Gen - C Plan Heating System? Help!

[Johnmdc]

Yes the heatlink would go in place of the clock.

Clock. Nest
5. N
6. L linked to 2 and 6 (not 5 as it would usually be.)
2. 3 linked to 4 valve feed
1. 5 (not 6 as usual) boiler and pump probably 2 wires
4. Earth

 

[Johnmdc]

Stem's diagram is almost correct except the pump live should be in 5 with the boiler live not 4 and the valve live in 3.
That diagram is for a gravity hot water pumped heating system.
Edit. As he explains I hadn't read his comments on it.

 

[djsmith83]

Stem's diagram is almost correct except the pump live should be in 5 with the boiler live not 4 and the valve live in 3.
That diagram is for a gravity hot water pumped heating system.
Edit. As he explains I hadn't read his comments on it.

Ah cool, so his diagram with edits he made is fine. And it will call for hot water fine?

 

[Johnmdc]

Yes.

 

[DP]

I’m sorry Stem but the above wiring diagram is incorrect (it won’t work).

Wildcat, why will it not work.
Which diagram
One posted at 10.50?

 

[djsmith83]

@DP i think @Wildcat1961 was referring to @stem diagram without seeing the edits he also wrote - right @Wildcat1961 ?

 

[stem]

I’m sorry Stem but the above wiring diagram is incorrect (it won’t work).

All I can say is that it worked when installed. I will try to explain how I got there:

First of all don't forget what I said regarding the diagram:

Below is a wiring diagram I did for someone else. The only difference with your installation is that, where I have shown the boiler connected, in your case, it will be the boiler and the pump, and where I have shown the pump connected, in your case it will be the motorised valve.

djsmith83, when I get back on my laptop tomorrow, I will revise the diagram for your application. I'm not going to attempt it on a tablet. Who know what it will end up like.

1. When hot water only is set 'on' (5) and (6) are connected together by the Nest. (6) is connected to the live, (5) becomes live and so the boiler and pump operate and pump hot water only around the hot water cylinder. The radiators don't heat up because the motorised valve remains closed.

2. When heating only is 'on' (2) and (3) are connected together by the Nest. (2) is connected to the live, so (3) also becomes live and the motorised valve opens. As hot water is not required, (4) and (5) are connected together by the Nest (4) is connected to (3) by a link, so when the heating comes 'on' (5) also becomes live via the heating section of the Nest and the pump and boiler operate. This is the 'fly in the ointment' bit, because as the boiler and pump need to run for the radiators, the hot water will also heat up. But this is because of the plumbing restrictions. Wiring it like this avoids having to check that the hot water is set to be 'on' at exactly the same time as the heating. Selecting the heating 'on' also selects hot water 'on' for you automatically.

3. When heating and hot water are 'on' (5) and (6) are connected together by the Nest. (6) is connected to the live, (5) becomes live and so the boiler and pump operate. Also (2) and (3) are connected together by the Nest and the motorised valve opens. Water is thus pumped around the hot water cylinder and also the radiators.

 

[djsmith83]

All I can say is that it worked when installed. I will try to explain how I got there:

First of all don't forget what I said regarding the diagram:
djsmith83, when I get back on my laptop tomorrow, I will revise the diagram for your application. I'm not going to attempt it on a tablet. Who know what it will end up like.

1. When hot water only is set 'on' (5) and (6) are connected together by the Nest. (6) is connected to the live, (5) becomes live and so the boiler and pump operate and pump hot water only around the hot water cylinder. The radiators don't heat up because the motorised valve remains closed.

2. When heating only is 'on' (2) and (3) are connected together by the Nest. (2) is connected to the live, so (3) also becomes live and the motorised valve opens. As hot water is not required, (4) and (5) are connected together by the Nest (4) is connected to (3) by a link, so when the heating comes 'on' (5) also becomes live via the heating section of the Nest and the pump and boiler operate. This is the 'fly in the ointment' bit, because as the boiler and pump need to run for the radiators, the hot water will also heat up. But this is because of the plumbing restrictions. Wiring it like this avoids having to check that the hot water is set to be 'on' at exactly the same time as the heating. Selecting the heating 'on' also selects hot water 'on' for you automatically.

3. When heating and hot water are 'on' (5) and (6) are connected together by the Nest. (6) is connected to the live, (5) becomes live and so the boiler and pump operate. Also (2) and (3) are connected together by the Nest and the motorised valve opens. Water is thus pumped around the hot water cylinder and also the radiators.

Awesome! Thanks @stem - extremely helpful! Sent you a DM also.

 

[stem]

The revised drawing is attached.

I notice that you haven't given the actual model details for your "late 90's Gloworm" so I haven't been able to check the specific wiring details for your boiler. Some boilers have what is known as a 'pump overrun' which keeps the pump going for a short while after the boiler goes off to dissipate residual heat. Although your boiler is fairly old, some boilers around that time were being equipped with it. If yours does have this facility, instead of connected the pump directly to the boiler L & N as shown below, the boiler will have a special set of terminals provided specifically to connect the pump to. And an additional permanent 'Live' connection. If you post back the details of your boiler I can check this.

The motorised valve, as well as having L & N wires probably will have grey and orange wires. If so, these can be ignored and shouldn't be connected to anything.

 

[djsmith83]

Thanks for this @stem , awesome. Heres the boiler (see attached pic):

 

[stem]

Then no pump overrun. The drawing is OK as it is.

 

[djsmith83]

Amazing, thanks @stem

 

[djsmith83]

@stem hi mate - quick one. Got an electrician coming tomorrow to fit the nest according to your diagram. As I haven’t got a thermostat currently and have the Randall controller/clock (which will be getting replaced with the heat link, right?) I’ll be using the nest stand and the USB power cable to power the stat. Does this change anything when it comes to the installation and your wiring diagram?

The stand is the only way of powering the nest if you don’t already have a thermostat right? Or is there another way of powering the nest stat while it’s mounted on the wall rather than the stand?

Thanks in advance!!

 

[picasso]

Why not get a plumber in to install a second 2 port valve and cylinder stat ?

 

[stem]

@stem hi mate - quick one. Got an electrician coming tomorrow to fit the nest according to your diagram. As I haven’t got a thermostat currently and have the Randall controller/clock (which will be getting replaced with the heat link, right?) I’ll be using the nest stand and the USB power cable to power the stat. Does this change anything when it comes to the installation and your wiring diagram?

The stand is the only way of powering the nest if you don’t already have a thermostat right? Or is there another way of powering the nest stat while it’s mounted on the wall rather than the stand?

Thanks in advance!!

The Thermostat can be powered either from the Heatlink T1 & T2 terminals as per my diagram, or you can use the separate plug in Nest power supply, it doesn't effect the rest of the Heatlink wiring.

As the wires are already in place at the existing timeswitch, that would be the easiest place to install the Heatlink it. But it reality it can be installed wherever you like but the wires would have to be moved.

Picasso makes a good point which has been mentioned a few times previously, but of course it's your choice. It would involve additional wiring.