Honeywell ST9400 wiring

[David Owens]

Hello, I have been replacing my home CH with a TDAO set up. All went well until I came to replace the Honeywell ST 9400 programmer with the Tado extension kit. The question I have is related to this picture. Tado say the ST is wired up incorrectly. Can anyone confirm this?
No wires at all were connected to the 1, 2, 3 or 4 terminals and two wire have never been connected.
Tado have said they can't help.

 

[stem]

Assuming that the wires in terminals L and N are actually connected to L and N somewhere at the other end. Then there is a mains supply present to provide the programmer with power, so it might appear to operate. However the heating and hot water system control wires should be connected to terminals 1 to 4, which are vacant, so it isn't actually doing anything at all.

The ST9400 is a dual channel programmer designed to give time control of central heating and stored hot water heating. So, as a minimum, there should be a wire in terminal 3 which controls the hot water and a wire in terminal 4 that controls the central heating.

Looks like your system may have been modified or maybe changed for a combi boiler etc., since the ST9400 was installed and the controls are now somewhere else. That unit seems to be just functioning as a junction box.

 

[David Owens]

That’s exactly in line with what Tado said and is what I guessed. Why would someone wire it up that way? It was professional installed. Thank you for the reply.

 

[stem]

I've no idea why it's wired like that, you would have to ask the installer. I would hesitate to use the term professional though. So what does now provide the time control for your central heating?

 

[David Owens]

I knew something was wrong because the thermostat over-ruled the programmer. I used to turn it down low at night.
Now individual Tado TRV’s and thermostat run the system. Problem only came to light when I started to instal the hit water extension kit. I will get someone to come and have a look!

 

[stem]

Do you have a stored hot water system then? If so, what is controlling the times that the hot water cylinder is heated up?

 

[David Owens]

An excellent question. The Honeywell obviously didn’t do it. I’m completely lost.

 

[David Owens]

The St 9400 was fitted as a replacement installed by a local company in March 2019. They must have wired it up this way? Evo homes. I should probably give them a call.