How to replace a Honeywell ST9400C Controlller?

[Ala5dair]

Hi.
Whilst stripping wallpaper in our utility room, I think I may have damaged our ST9400C controller. The clock is currently “stuck” at 3:30 Sun, with the override on the heating on. Pressing “ok” and “minus” for 8 seconds doesn’t do anything and I can’t find a reset option.

I’m planning on replacing it, and I understand that it’s a simple thing with all connections made to a separate wall mounted plate. However, when I power down the main CH switched spur, the backlight goes off, but the LCD remains lit. Is this because of the internal battery, and can I safely remove the front with the LCD on?

is there anything else I should be aware of?

 

[Ala5dair]

Replying to my own post, as I’ve called Honeywell today.... The LCD is staying on because of the battery back-up. It’s a 2032 coin battery and it will last 90 mins. So, I was advised that it would be safe to remove the controller from the back plate after powering down mains but with the LCD showing. However, if I was concerned, I could wait until the LCD powered down and then remove it. The battery is replaceable.

I’ve not done this yet, as the controller has failed with both heating and water in the “on” position and I’m reluctant to risk losing this by removing the panel to see if it’s repairable, and then having neither until a new controller arrives. I’ll probably bite the bullet and order a replacement....

 

[ianmcd]

Try entering installer mode and go to paramiter 8 and reset all settings, this tells you in the installation instructions how to enter it, if you dont have the instructions just google ST9400C installation instructions, loads on there

 

[Ala5dair]

Try entering installer mode and go to paramiter 8 and reset all settings, this tells you in the installation instructions how to enter it, if you dont have the instructions just google ST9400C installation instructions, loads on there

Thanks, but all buttons are inoperable. Pressing “ok” and “minus” for 8 secs as instructed (or even 20 secs) has no result. I’ve concluded that I’m buggered and the unit needs replacing.

 

[ianmcd]

As you say the backup battery should last 90 mins, leave it completely turned off for longer than that, then power it back up and see what happens, you have nothing to lose, if it doesnt work then you will need a replacement unit