Danfoss LP722 to 3rd Gen Nest Heatlink

[Garrick]

Good Morning Everyone.

I am aware there are various threads already on Nest installs but I have searched through all of these and cant find what I need to know.

Basically I bought a Nest 3rd Gen and swapped my Danfoss LP722 programmer for the heatlink. I used the Y plan wiring diagram and linked out the live to 2 and 5 and used the 3 and 6 terminals for CH and HW as stated.

However when I select heating only, it doesnt fire my boiler up, when i turn the hot water on via the app or thermostat it then puts the heating on also.

I have had a look in my airing cupboard and cant find a valve anywhere. I have also checked the relevant voltages in the heatlink and all looks as should.

I must also state that I am a qualified electrician so I would like to think I have some form of knowledge, even if not on boilers!

Any help would be much appreciated

 

[muggles]

Sounds like you've got the wiring wrong somewhere...unfortunately the vast majority of qualified electricians I've come across struggle with heating wiring, so you're not alone! Can you post some pictures of your airing cupboard and boiler? There must be a valve somewhere! If you've got a Y-plan then you also needed to connect Nest Terminal 4 - HW OFF. This goes to the grey wire on your 3-port.

 

[Garrick]

Hi I will do later

The boiler is an old Ideal Mexico Super 75. Like i said I find it strange that it works fine on the dual programmer but not on the Nest?

I had a look in the airing cupboard yesterday and all I can see are the various pipes going in to the tank, the immersion in the top (which isnt used). I also checked in the loft near the tanks up there and next to the boiler. I can see the pump but that is all

 

[Echo the husky]

Were you able to select heating only with your old controller?