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Honeywell Boiler Timer Install Replacing Greenbrook T107

Postby MrMe » Thu Nov 09, 2017 5:19 pm

Existing Timer
Evening all, I have today received my new Honeywell Boiler timer. I did say to the partner that I'd be able to install it but recoiled in horror when the back plates didn't match and I am now, sadly, not 100% on installing this thing. I'm sure I could make an attempt but I though I'd ask you kind folk which wire went where. The existing timer Greenbrook t107 fails to fire the boiler up unless you hit the 'boost' button. So I have this Honeywell ST9100C 7 day timer to install.

Lashings of thanks in advance.
Wiring diagram of new timer
And new timer
Existing Timer
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Simply Build It

Postby ericmark » Fri Nov 10, 2017 7:09 am

The Greenbrook t107 is to control immersion heaters and the like from off peak power not saying some one could not have got it to control a boiler, but only they know how they wired it, that is not what it's designed for.
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Postby Mr White » Fri Nov 10, 2017 7:49 am

If only life was as simple as put this wire here and that one there and then Robert would be your mother's brother, but sadly its not that easy.

Don't look at it as complicated, look at it as you have a vague idea and you need to find which cable does what.

A standard "programmer" is just an on / off switch that turns on and off at specific times. To do this it requires a supply, (Live and neutral) and then it needs something to switch, This is often just two wires, but sometimes it does a "change over" in which case it uses 3 wires.
What you (or any one helping you) have to do is to find out which wire does what and then connect it to the appropriate terminal. (None of this are counting the earth wires)

Look at the new programmer diagram, it has a supply pair and 3 (change over) for the switch.

The rest is up to you.
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