Wiring from Digistat to Honeywell

[karawara88]

I now have myself a honeywell cmt 927

But I am a bit confused on the wiring for the change over from a drayton digistat 3 which only has 3 connections 1 - 2 - 3

1 and 3 are connected and 1 is the permanent live

On the Honeywell I have six connections N L L A B C

It looks to me from the diagram which is not very clear that I have to link L & A and B is the permanent live and N is the neautral.

Am I right? help much appreciated.

[doitall]

What is the make and model of the boiler.

What controls do you have, Motorized valve etc.

[karawara88]

The boiler is a old Thorn Apollo and has motorised valve, and the timer is a sunvic select 207xl

[D_Hailsham]

As the exisiting stat does not have a neutral wire, you will need to run a new cable to the receiver, which can be near the HW cylinder/motorized valve. You should use 3 core cable (not twin and earth), e.g brown, blue and yellow.

Receiver end
Connect Brown to L
Connect L to A
Connect 3rd colour to B
Connect Blue to N

At the other end
Connect Brown to a permanent Live
Connect Blue to permanent Neutral
If you have a three port valve: Connect 3rd colour to white valve wire (remove the existing wire - this goes to 3 on your old thermostat)
If you have two 2-port valves: Connect 3rd colour to brown wire of CH valve and remove the existing wire which goes to 3 on old thermostat.

At the Sunvic, remove the wire from terminal 4 (CH ON) - this goes to 1 on your old thermostat.

The Sunvic 207 XL is a two channel timer, but the CH channel is now redundant as the CM927 will be in charge.


Hint
Before fixing the receiver in place, it is a good idea to check that the two parts of the CM927 communicate properly from their proposed locations.

Connect a long lead with a 3 pin plug on one end to the L and N terminals of the receiver and plug in. You can now do the communication test in the installation manual and try different receiver locations until you find the best one.

[karawara88]

Thanks for that, too complicated for me, I know my limits

Behind the current stat both cables have a neutral cable taped together and just the reds are connected to the current stat.

[doitall]

karawara88 wrote:

Thanks for that, too complicated for me, I know my limits Behind the current stat both cables have a neutral cable taped together and just the reds are connected to the current stat.

It's easy if you take your time and read what Dave has posted.

[karawara88]

Its not possible for me to start re-wiring, because its all inaccesable.

Currently I have two cables both have a red and black, the two reds are connected to the current stat the blacks connected together.

I do know which cable comes from the white valve port cable.

I wanted an RF stat that I could easily swap for my current one. Withe the messing about I may as well just drop my current cable down the cavity and locate in the lounge, lot easier and I know what I am doing.

Thanks for help though.

[D_Hailsham]

karawara88 wrote:

Thanks for that, too complicated for me, I know my limits

Have faith! I'm going to make it easier for you.

Quote:

Behind the current stat both cables have a neutral cable taped together and just the reds are connected to the current stat.

That make life much easier. You can forget my previous instructions and I will tell you how to put the receiver where your old thermostat was located.

One red goes to the programmer CH ON; the other red to the valve white wire. Separate the blacks at both ends.

Cable 1 (Red connected to thermostat terminal 1)
Connect Red to receiver L
Connect Black to receiver N

The other end of this cable has Red connected to programmer CH ON
Move Red to programmer L terminal
Connect Black to programmer N terminal

Cable 2 (Red connected to thermostat terminal 3)
Connect Red to terminal B
Disconnect the black at both ends and make safe.

Link L to A

This will bypass the CH channel of the programmer, which is redundant.

[karawara88]

Thanks Dave

Much appreciated I am up and running, the only thing is when I wired it all up everything was doing what it should but the boiler was not firing up, so I reconnected the programmer and the negatives and it worked !

I have never used the programmer it always stays on "on" for heating and water so I am happy to leave it as it is.

I will at some point in the near future have to get the boiler changed as its on its last legs. The biggest problem I have is whoever lived here before boxed everything in (even the programmer was plastered into the wall). so nothing is accessible if the pump packed up I would have to rip a wall down to get to it. !

Again many thanks you are a star.