Replacing a Honeywell ST9400

MickTreviss

Hello all, I am trying to fit a Tado V3+ starter kit and have a couple of questions if I may.
I have the live and the neutral but only 3 other wires in terminals 1,3&4, yellow, blue and red respectively with 1 being HW off, 3 being HW on and 4 being CH on could I ask what the equivalent is on the Tado Receiver please?
I have installed the Internet Bridge and linked to the Wireless Thermostat, I have also isolated the 2 wires from the discarded Honeywell Room Thermostat.
Any help would be greatly appreciated, thank you very much.

policywonk

This link: file-20223.pdf presents the wiring for your programmer

• PIN 1 wired to HW OFF
• PIN 2 wired to CH OFF
• PIN 3 wired to HW ON
• PIN 4 wired to CH ON.

Therefore, for now, park any wires connected to PIN 1 and PIN 2; but actually use these wires:

• NEUTRAL to NEUTRAL
• LIVE to LIVE and COM on
• The old wire on the Honeywell PIN 3 goes to Tado HW NO;
• The old wire on the Honeywell PIN 4 goes to Tado CH NO.

There is however much to be considered. You havent stated which specific Starter kit you purchased.

• Does it control hot water as well as central heating?
• Is your boiler controlled designed to be controlled digitally as well as in dumb on-off mode?
• Is this a house with an S Plan, Y Plan, W Plan…?

These make a difference to your choices and configuration. Can you describe your present setting a little more? We may be of more help….

MickTreviss

Hello and thank you very much for your kind reply, I have a Tado Starter Kit V3+ inc Programmer with Hot Water Control.The Honeywell programmer controls hot water and temperature.
The thermostat is a Honeywell and is wired and is a DT90E 1012
I don’t know if the system is S, Y or W, sorry
Do I join the 2 wires at the thermostat or isolate them please?

I am really appreciative of any more guidance you can provide me, thank you very much.

wateroakley

Hello @MickTreviss Welcome. The picture (and very neat wires) suggest you have a Y-Plan (fully pumped with a 3-port mid-position zone valve, hot water priority). Or C-Plan (Pumped heating and gravity hot water). The 'most likely' bet is a 3-port zone valve.

(Honeywell ST 9400) to Tado wireless receiver translation is straightforward. That's the very common programmer that we replaced in 2022 with a Tado wireless receiver.

(N) to N. (L) to L. (1) to HW NC. (2) not used. (3) to HW NO. (4) to CH NO.

Tado wireless receiver: Link L to CH COM to HW COM. Links should be in the starter pack.

It is important to know if you have a Y-Plan or C-plan heating system, as that affects the configuration setting for the wireless receiver.

Join the wires on A and B at the DT90 thermostat with a Wago connector from the starter kit.

Screen grabs of the Honeywell wiring …