Google Nest Thermostat on Y Plan - White cable from motorised valve

[Ant1]

I currently have a Y plan Central Heating system, my junction box is unusual as it contains a Omron MY4 relay, i.e. a relay that controls 3 ports RL1, RL2 and RL3 as shown from the wiring diagram below:

I would like to replace my programmer with a Nest Heat Link and the room thermostat by a Nest Thermostat. I am confident how to wire the Nest Heat Link and Thermostat (refer to second wiring diagram below), however since my junction box is using a Omron MY4 relay I do not think I can simply connect the white cable of the motorised valve to connector 3 of the Nest Heat Link. Instead I believe I should simply install a jumper cable between connectors 1 and 3 in my current junction box (shown in red) which would effectively "simulate" the original thermostat to be permanently forced to ON. Would you agree?

 

[ianmcd]

on your 1st diagram where it says typical programmer, use those wires to connect to your nest heat link,leave everything else as is

 

[ericmark]

It is not a standard three port valve read this thread and consider if you want to touch it?

I think your diagram will likely work, however I would be worried after reading the other thread about using that three port valve, and would say this is not the time of year to do the job, I would wait for warmer weather first, so if anything goes wrong, you have time to fix it.

 

[Ant1]

Hi Ian, since I want to use the Nest thermostat in situ of the old room thermostat (I will route the 12V from the Nest Heat Link using the existing wires), I believe the second diagram is pretty accurate.

Hi Eric, the thread you pointed out was mine. At the time I had to do a temporary repair (the junction boxed got damaged as not protected by the correct fuse), the whole junction box has been replaced some time ago and working fine. The MK1453 valve comes with a DM5601 actuator, it is motorised and does not make use of a spring, why do you say it is not a standard 3 ports valve?

 

[ianmcd]

Hi Ian, since I want to use the Nest thermostat in situ of the old room thermostat (I will route the 12V from the Nest Heat Link using the existing wires), I believe the second diagram is pretty accurate.

I am talking about the nest heat link not the thermostat, Have you bought the correct Nest ? does it look like this ?

 

[ianmcd]

Im betting you have actually bought a Nest E and not a nest, they are not the same thing

 

[Ant1]

Yep, I bought a Nest (as shown in your photo), not a Nest E.

 

[ianmcd]

Yep, I bought a Nest (as shown in your photo), not a Nest E.

So where are you planning on installing the heat link ? edit, sorry just noticed you are replacing the programmer with the heat link yes that will work

 

[Ant1]

Sorry my second diagram was a bit misleading as the Heat Link was titled as Thermostat, I have now uploaded a more accurate diagram with the devices being properly named.

 

[Ant1]

Just for completeness, and to help people using a Relay Junction Box RJ 2802 (Satchwell Sunvic 437-2-802) together with a DM5601 actuator (for a MK1453 3 port valve), I wired my Google Nest according to the above diagram and everything works fine.