Nest wiring question

[JTplumbingservices]

If this is going into an existing system with a programmer and room stat is it just a case of wiring the nest stat into the old room stat and the heat link into the old programmer wires?
Cheers

 

[ShaunCorbs]

What system combi or s plan

 

[JTplumbingservices]

Sorry, combi.

 

[ShaunCorbs]

Best to remove the wiring and fit receiver below boiler you need to be gas safe to do this if the wiring is behind the main cover

 

[JTplumbingservices]

I passed my gas on the 19th of December.. just waiting on my certificate now
Ive been a time served plumber since 2006 but our company didn’t do gas work so we had to sign something to say I wouldn’t be able to sit my assessments.
My current company is the first since then who agreed to put me through it so now I’m trying to educate myself on heating controls, fault finding etc