Nest to replace Honey well ST9100C and two CM907

[nhwebforge]

Hi guys

I'm looking to replace my current setup with a Nest solution. At present I have a Potterton Proax 15SL boiler in the kitchen and a hot water tank in the airing cupboard. In the airing cupboard I have a Honeywell ST9100C timer for controlling hot water and overall central heating. I have two Honeywell CM907 timer/thermostats, one on each floor controlling that floor's radiators via powered valves in the airing cupboard. It's a fairly recent install - the house is only 6 years old.

So my question is: I'd like to replace the thermostats with Nest Gen 3's. I presume the existing twin cables going to each thermostat will have to be repurposed as power cables for the Nest thermostats. However, my knowledge runs out at where and how to connect the Heatlink. Again I presume I need two Heatlinks. One per floor, both in the airing cupboard. Do these connect to the powered valves in the airing cupboard (one for each floor marked 1st and 2nd in the photo) but I also have a third valve marked HW. Guess this means hot water but no idea what this valve is controlling. Will one of the Heatlinks control the hot water? Finally there are two pumps. One is for the CH I guess but the second smaller one - no idea. In fact, the previous owner appears to have unplugged it as it's fairly noisy but I haven't noticed anything not working properly as a result. Do these pumps need somehow linking into the Nest system?

I guess it's the two Nest and two Heatlink setup that's confusing me. One will control hot water and one floor's heating and the second just the other floor's heating with no connection to the hot water, right? Or wrong?

Valves and pumps are connected to a huge junction box in the airing cupboard as shown in the photos.

I apologise. I'm a real beginner at heating systems. Very proficient at home automation. But very confused by heating!

Thanks in advance for any pointers you can give me!

Nick

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• 24 Apr 2020

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• 24 Apr 2020

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• nhwebforge
• 24 Apr 2020

 

[ericmark]

Nest is not designed to run as pairs, it would work Nest Gen 3 plus a Nest e, but EPH wall thermostats are designed to work together so would be a better option, Drayton also do a 3 and 4 zone programmer.

 

[Johnmdc]

You can have as many nests as you want. I added 3 to a house that already had 8 fitted.
Add you say you will need 2 one to control the hot water and one heating zone and another to control the other heating zone.
The heat links would both be installed in the airing cupboard and wired into the box you have shown.
And also as you say the existing wires to your old thermostats can be repurposed to power the new nest thermostats.
As to how it is all wired will be a bit complicated.

 

[Johnmdc]

The other pump looks like a brass pump which is used to circulate the domestic hot water around your house so that it doesn't take long to come out of the hot water tap when you turn it on.