Installing Drayton Wiser 3 channel confusion!

6 Feb 2021
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United Kingdom
Hi, hoping someone will be able to help me here as am certainly a novice when talking about central heating controls!
I'm replacing standard heating controls for a Drayton Wiser Heat Hub 3 channel.
I have a Vaillant Ecotec 810 boiler, unvented hot water tank, Honeywell C27 programmer, manual stat downstairs hallway for all house heating(1), and a separate digital stat for conservatory heating (2).
Have managed to get hot water and main heating working fine through the wiser but stuck on (2) heat channel.
It appears the C27 is only two channel and I can't work out where (2) is going.
The backplate for the C27 has 3 live wires connected to L so was assuming (2) had been wired on to L to get round the limitation of the C27. Removing one of the live wires at a time produces following results;
Live 1 removed - boiler doesn't power on / heat hub doesn't power on
Live 2 removed - boiler doesn't power on / heat hub powers on
Live 3 removed - boiler powers on, hot water symbol on boiler, but doesn't get call from hub to fire up, and no heat symbol on boiler / hub powers on

Not sure what to check next.
Have attached pic of the backplate wiring (3 and 4 have been moved to 2 and 3 for the Wiser now).

Thanks for reading.
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The C27 as you say, is a two channel programmer.


One channel for the hot water is connected to terminal 3 [HW on]. The other channel for the central heating is connected to terminal 4.[CH on]

You presently have two room thermostats, one in the hallway and another in the conservatory. As you don't say otherwise, I'm assuming that the heating in both the conservatory and main house are presently connected to the same boiler (ie the conservatory heating isn't on a separate or electric system) and that both house and conservatory heating are presently controlled by the heating channel of the C27. [If this is not the case post back with the correct details.]

If this is the case, both thermostats will be supplied via the wire presently connected to terminal 4. To install a 3 channel Wiser, you will have to physically trace the conservatory heating wiring and separate it from the main house heating wiring. Then reconnect it to the wiser third channel.

The old thermostats should be decommissioned which involves removing them and making a wiring modification to bridge their switching wires to complete the circuit.
Thanks for taking the time to reply.
To be honest I'm not sure if the conservatory heating was being controlled by the C27. I spoke to a Drayton support engineer who said it should be, but the CH on light never lit up when conservatory heating was on.
Is there another way it could be connected to the boiler? I know it was fitted later than original heating as it was part of an extension.
If the conservatory heating is not controlled by the C27 programmer and the Conservatory is fitted with a programmable type thermostat (ie one that gives both time and temperature control) then based on your description where you mention ‘3 live wires’ I assume that you are referring to the wires in the L terminal [the wires in terminals 3 & 4 are also live wires] I suspect that:

Wire 1 in L is the main supply from the fused spur [no power to either the boiler or hub when removed]

Wire 2 in L is the live supply to the boiler [no power to boiler, but power to the hub when removed]

Wire 3 in L may be the live supply to the thermostat in the conservatory

Although I’m not sure what you mean by your description regarding the function of wire 3
boiler powers on, hot water symbol on boiler, but doesn't get call from hub to fire up, and no heat symbol on boiler / hub powers on

If my theory is correct, I would expect that with live wire 3 removed, that the main house heating and hot water should work but the conservatory heating will not. If so, this will be the wire for the 3rd zone of the Wiser.
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Yes, sorry you are correct when I say three wires in the L connection of the back plate.
To try and explain Live 3 a bit better. The boiler has a tap (water) and a radiator (ch) symbol on the display when fully functioning.
When I remove live 3, just the tap icon displays. If I try and boost the water using the Wiser hub, nothing appears to happen with the boiler.
Hope that makes a bit more sense!
With that being the case, do you think it's worth connecting live 3 to terminal 1?
Sorry, it's not quite that straight forward whether the thermostats are calling for heat or not effect what the boiler shows, not just the wiring.

First of all, what have you done regarding the now redundant existing hall and conservatory room thermostats?

With the "live wire 3" disconnected, does the heating in the main house work as it should, and the conservatory heating not work?
Just as an update, you were spot on, the Live 3 was the conservatory heating circuit. Once connected to terminal 1 on the backplate all started working as expected.
Now to look at removing the stats from the circuit, but think(!) I'm good with that...
Thanks for all your help, much appreciated.
Excellent and thanks for the update. (y) If you need any help with the old thermostats post back.

It's a good idea to get it up and working first before removing the original stats. Then if there is a problem (hopefully there won't be) then it's easier to narrow it down.

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