Replace Honeywell ST9400C with Drayton Wiser

1 Aug 2022
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United Kingdom
Hi all - I'm looking to replace a Honeywell ST9400C with a 2-zone Drayton Wiser. The Honeywell controls the heating and hot water and has the following wiring:


I thought I could simply remove the Honeywell and replace it with the Wiser unit without changing the wiring but clearly not as the hot water timer switched the boiler on but put it to the heating rather than the hot water tank.

I've looked at other posts but they seem different to my problem as they talk about external thermostats etc. Can anyone please give some guidance on how to go about this please?

Many thanks
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There are 4 versions of Wiser, Single, Double, and Three zone plus an OpenTherm option, but double should be same wiring as Honeywell ST9400C but would need the old thermostat removing.

You need a brown sleeve on the CH ON wire, wonder if you have got wires mixed up?

Since you have a HW off wire I would assume Y plan, so with hot water only the motorised valve does nothing. The tank thermostat does all the work, it would be unusual not to have one.
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As per @ericmark - either you have the wrong version of Wiser or wired up wrong. Did you transfer wiring like for like?
You have earth, neutral, live, then DHW off, which goes to three port valve so when CH running the valve will motor all the way across, so no hot water, then gap, then DHW on which should go to the tank thermostat, and from there to boiler and pump, it does not work the motorised valve as default is DHW, and finally CH which works motorised valve which in turn works boiler and pump.

The Wiser installation guide shows how the same plate is used with three different controllers
Tado also do the same, and Hive use first two, which to my mind is asking for problems as the one channel is volt free, but 2 and 3 channel are not, there is also an add on module for OpenTherm with a further 4 connections, although only 2 seem to be used.
It says the OpenTherm is only for single channel, but seen reports saying it does still work with multi-channel.

I really can't see the point with most homes in double zoning the central heating, unless using part of the home as a flat or shop etc, the TRV's form zones so no point in further zones, but for some reason it seems many homes are double zoned.
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Thank you for your replies. I'm not really sure what to do.

It's definitely wired the same as I replaced the backplate to accommodate the two zone wiser unit, which didn't work as per my original post. I then put the Honeywell unit back on the wiser backplate and everything works perfectly.

My house has an oil fired boiler, a hot water tank, radiators with thermostatic valves and the Honeywell programmer on the wall. There is no additional thermostat etc.

I'm thinking I might need to get someone to look at it as it sounds like it should have worked but the fact it hasn't has highlighted my lack of knowledge!
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So there’s no room thermostat? You may have a C plan setup.
So there’s no room thermostat? You may have a C plan setup.
its a Y plan mate as per the origional wiring, if the OP copies the wireing to the 2 zone a, the middle diagram in @ericmark post above it should work
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its a Y plan mate as per the origional wiring, if the OP copies the wireing to the 2 zone a, the middle diagram in @ericmark post above it should work
Thank mate, I did think that, but then I saw this wiring diagram and got a bit confused, as terminal 1 goes to 7 but appears to do nothing.


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I do have the N/C contact used with my C Plan, but that is with Nest, which has volt free contacts, with Hive I know it is a software fix, one contact for pump, one for boiler.

However a two zone Hive, Drayton, Honeywell all use same base plate so should have worked, may be not two port?
Start again from the beginning, step one work out what Plan you are using, telling one to feel a zone valve lever to see if valve open or closed does not help when we don't even know if you have zone valves.

I remember trying to work out why daughters central heating had stopped working, turned out there had been a problem for years, and previous owners had latched a zone valves to get around the problem, and my son-in-law had knocked the lever off the latched position while tiding up airing cupboard.

Not that I think that is likely in your case, but to guide you through, we need to know what system. We look at

We have earth, neutral, live, then hot water off, which makes me think Y Plan which would have a three port valve, then unused, and then DHW and finally CH the blue wire, which should really have a brown sleeve on it, or at least some brown tape, however the count is wrong, three browns but seems to be only two blues and earths.

So likely some blue wire we can't see, and an earth wire we can't see, so thought is wrong blue wire used.

So likely a wiring centre which is likely near the motorised valve, and often we can work out what does what from the core colours of the motorised valve, other wires can be any colour, but the motorised valve comes with cable so core colours can direct us.

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