New thermostat - Honeywell CMT727 with Worcester Greenstar 28i Junior boiler

Discussion in 'Plumbing and Central Heating' started by BlackBook, 18 Apr 2016.

  1. BlackBook

    BlackBook

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    Hi!

    I think that I've got this one figured out, but thought it prudent to ask the experts just for reassurance!

    My current setup is a British Gas WR1 (properly known as a Drayton Digistat SCR) connected with a 4-core (plus earth) cable that runs to a circuit board within a Worcester Greenstar 28i Junior (combi boiler) drawing on 230v. The circuit board is subsequently connected to the mains.

    The Digistat had been operational for approx 7 years, but finally gave up the ghost (no lights but would make a clicking sound when recommissioning and trying to paid up with the Drayton in an attempt to pair up with the Drayon +RF transmitter. Having read numerous bad reviews about this receiver model, I'm counting myself lucky and have bought a better receiver - a Honeywell CM727 which comprises of an HC60U receiver unit and a CT727S1106 wireless room unit.

    Looking at the wiring for the current setup (image 1) the black wire is connected to common (terminal 1) and the grey wire is used to call for heat (terminal 3). My suspicion is that, with regards to the Honeywell unit (image 2), the black wire goes to A and the grey goes to B

    Does this seem correct? Do I need to change anything on boiler circuit board?

    All comments gratefully received!
     

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  2. TCCHeating

    TCCHeating

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    Yes. That is correct

    No
     
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  4. BlackBook

    BlackBook

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    Thanks for such a quick reply - lightning fast!

    One other thing - with regards to the earth wire, should I terminate and insulate it or should something else be done with it? Not using the earth wire just doesn't feel right!
     
  5. stem

    stem

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    If the HC60U doesn't require an earth connection, you should terminate and insulate it, so that it doesn't inadvertently come into contact with something it shouldn't. The original SCR was the same really. Drayton provided a useful terminal to 'park' the earth in, but it isn't actually connected to anything.
     
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  7. BlackBook

    BlackBook

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    Ah, ok - thanks for his. I was a bit confused about it having an earth terminal, which appeared to slightly contradict its installation guidance which states that it doesn't require an earth connection as it's double insulated.
    Thanks!
     
  8. DIYnot Local

    DIYnot Local

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