Nest thermostat on a gravity only hot water / pumped heating?

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cgrexy

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Just wondering if it is possible to have a nest on my heating system?

The hot water runs on gravity only. The heating is on a pump.
For the heating to work the water has to be live too.

There is no valve, on cylinder stat. I know the system is old. I’d just like to have it working with the nest till new year when it will all be replaced.

So I have a live wire for the heating and a live for the water (that also fires the boiler)

So when the heating live is switched, the water live needs to be switched too. How would I wire this on the heatlink on the nest?
 
You would need to put a relay to operate with the room stat to bring on boiler and pump.
 
picasso said:
You would need to put a relay to operate with the room stat to bring on boiler and pump.
Click to expand...

So basically put a relay from the nest to switch both the pump live and water live when it asks for heating? This would then disconnect when heating isn’t asked for.

As below?

21BC8893-0306-44A0-8671-A069D0565659.jpg
 
Called C type the old system had a physical stop on the programmer to stop you selecting central heating only. There was nothing to tell the boiler to switch off when the domestic hot water reached temperature.

The was also nothing to stop the water thermo syphon in upper floor radiators.

The times set was what did the ballance between hot water and heating normally two on periods a day.

Although you could use Nest the question is why? It is putting cart before the horse. First job would be to fit a motorised valve in the domestic hot water.
 
ericmark said:
Called C type the old system had a physical stop on the programmer to stop you selecting central heating only. There was nothing to tell the boiler to switch off when the domestic hot water reached temperature.

The was also nothing to stop the water thermo syphon in upper floor radiators.

The times set was what did the ballance between hot water and heating normally two on periods a day.

Although you could use Nest the question is why? It is putting cart before the horse. First job would be to fit a motorised valve in the domestic hot water.
Click to expand...

New system in the new year, the programmer / timmer is currently bust. I can use the nest with the new system, so wanted to use that just for now and then move to new system.

Current system was fitted in 1974 and has really been trouble free. I know it wasn’t the best design, but it’s not worth a valve and any other work.
 
You can do it without a relay if you do the wiring to the nest slightly different.
Connect L and N as normal
Link L to 2 and 6 (instead of 5)
Connect pump to 3
Connect boiler to 5 (instead of 6)
Then also link 3 to 4
This way when you just set heating it will fire the boiler up as well as the pump.
 
Johnmdc said:
You can do it without a relay if you do the wiring to the nest slightly different.
Connect L and N as normal
Link L to 2 and 6 (instead of 5)
Connect pump to 3
Connect boiler to 5 (instead of 6)
Then also link 3 to 4
This way when you just set heating it will fire the boiler up as well as the pump.
Click to expand...

Great, I’ll give it a try before using the relay.
 
Johnmdc said:
You can do it without a relay if you do the wiring to the nest slightly different.
Connect L and N as normal
Link L to 2 and 6 (instead of 5)
Connect pump to 3
Connect boiler to 5 (instead of 6)
Then also link 3 to 4
This way when you just set heating it will fire the boiler up as well as the pump.
Click to expand...

Thanks Johnmcd. Obvious in the end but it did puzzle me how to achieve this.

[GALLERY=media, 101673]NEST - Gravity HW / Pumped CH by ziggy_zero posted 22 Jul 2018 at 5:31 PM[/GALLERY]

Regards,

Ziggy
 
Last edited:
You are the same person that asked and answered the question, are you not?
 
No. I have only just registered today. Cgrexy asked, johnmdc answered and I posted a follow up to say that it worked for me.
 
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