Nest Thermostat and Gravity Fed System

[SMJA]

Hi, can anyone help?

I had a Hive system running my Heating and Hot Water, just been given a Nest and thought I would give it a try. I have an old system which is Gravity Fed and with the Hive I simply held a button down and it went into 'Gravity Mode'. Don't seem to have that with Nest unless I have missed something?

Nest is fitted but doesn't switch my boiler on when the central heating is called but does seem to power up the pump. When Hot Water is called the boiler fires up but as expected the CH does not come on.

I seem to have a very basic system with L, N and HW ON and CH ON only. I have checked various diagrams and jset up as instructed, jumping the N to 2 and 5 on the Nest Heatlink.

Does anybody have any ideas? I'm missing that Hive now.

 

[ziggy_zero]

NEST - Gravity HW / Pumped CH

• ziggy_zero
• 22 Jul 2018

Then go into Settings >> Pro Setup on the Nest Thermostat. Set CH to On/Off and then HW to On/Off.

Regards,

Ziggy

 

[stem]

The Hive is designed for Gravity systems and can be configured in the settings for such. The Nest isn't, so a bit of jiggery pokery with the wiring is required, as per Ziggy Zero's drawing, but it has been done many times.

The connections might not be what you would expect. Connecting the Nest hot water 'common' terminal to the boiler for example. But it does work. There's a thread here, with confirmation from the OP if you want an example, and can be bothered to trawl through to the end.

The drawing below might be a bit clearer for you to follow. You don't have to connect the Nest Thermostat to the Heatlink [T1 & T2] and can use a plug in power supply instead if preferred.

 

[sweet]

NEST - Gravity HW / Pumped CH

• ziggy_zero
• 22 Jul 2018

Then go into Settings >> Pro Setup on the Nest Thermostat. Set CH to On/Off and then HW to On/Off.

Regards,

Ziggy

In this diagram what is preventing the boiler firing when heating and hot water are switched off?

 

[EFLImpudence]

Because 5(boiler) is connected to 4 & 3, but 2(Live) is connected to 1; not 3 & 4.

 

[FUSESvc]

The Hive is designed for Gravity systems and can be configured in the settings for such. The Nest isn't, so a bit of jiggery pokery with the wiring is required, as per Ziggy Zero's drawing, but it has been done many times.

The connections might not be what you would expect. Connecting the Nest hot water 'common' terminal to the boiler for example. But it does work. There's a thread here, with confirmation from the OP if you want an example, and can be bothered to trawl through to the end.

The drawing below might be a bit clearer for you to follow. You don't have to connect the Nest Thermostat to the Heatlink [T1 & T2] and can use a plug in power supply instead if preferred.

View attachment 145355

Put a nest on a system and wired it like for like. Customer came back to me and said his CH only works when the water is calling too. Put it down to a faulty zone valve and told customer to call a plumber. Plumber attended and informed me it was a gravity fed system and I have wired it wrong. Was pretty arrogant TBF. Called on my mate who is a top class heating engineer and he said the wiring might need jiggling. So I thought I might put a relay in circuit so when CH is calling it switched HW too. Did some research and ended up here. Seeing your diagram I instantly got it. No relay needed. Great solution. The old timer must have had an internal link fitted or a switch that I have seen on some timers. Anyway, buzzing now. Thank you so much.