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How to install the app on iOS

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Got it 🙂
 

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This assumes that all the wiring centre power is coming from the same supply circuit as the boiler.
That is the proper and most likely arrangement.

But if you get issues with an rcd tripping (not MCB) then that would point to them being on different circuits from the consumer unit, which would need to be corrected.
 
I believe i understand this now 🙂

The black wire which enters to the bottom of the Room STAT/Timer block link is carrying power which is carried over through the link into the red wire leaving the bottom and activates the demand for central heating. Hence the boiler firing constantly.

By removing the link and placing the black wire in the 4th position (counting from the earth as number 1) as soon as the thermostats activate, power travels down the black wire and the demand for central heating fires the boiler.

Is my understanding correct?

Edit correct
 
To be sure to be sure, remove the link and check for power at terminal 4 (from left)) if 230V there and 0V at termina 3 then black wire goes to terminal 3 .
 
That's great news.

During all the time your boiler was running on/off with the zone valves closed how did the boiler have minimum circulation?
Is there a ABV installed and if so is/was it noisy in operation, if installed, what make.
 
Your boiler may have its own internal by pass which must be pretty good otherwise all that running with no flow wouldn't have done the Hx any good or maybe its stainless.
 

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