Need to replace faulty Honeywell ST9400C

A package arrived, from Honeywell, this morning with a replacement programmer enclosed. I replaced the programmer, set the times and ran it through a test sequence. The system now appears to be functioning correctly. I will monitor it over the weekend but the prognosis looks promising.

Thanks to everyone who took the time to respond and to those at this thread //www.diynot.com/forums/plumbing/honeywell-st9400c-timer-and-no-hot-water.358649/#2932507

Also, thanks to those at Honeywell UK, who were very helpful.

Regards.

MartinFP
 
Sponsored Links
I have a problem with my Honeywell ST9400C and read the info on this site. Thank you to all those that posted about the faulty batch from 1037 - 1139.
I've just come off the phone with Honeywell and they are sending me an FOC replacement. It will take approx 7 days to arrive from the Netherlands.

FYI the date code can be found without removing the unit from the back plate. Set the main switch to run and hold the plus(+) button until the code is displayed on the screen. Ignore the "Invalid Code" displayed and the return to the normal screen. Just keep holding until the code is displayed. My code on the back plate read 1112 and the display read 12 11

This date code display screen will automatically return to the normal settings screen.
 
XaiviaX said:
I have a problem with my Honeywell ST9400C and read the info on this site. Thank you to all those that posted about the faulty batch from 1037 - 1139.
I've just come off the phone with Honeywell and they are sending me an FOC replacement. It will take approx 7 days to arrive from the Netherlands.

FYI the date code can be found without removing the unit from the back plate. Set the main switch to run and hold the plus(+) button until the code is displayed on the screen. Ignore the "Invalid Code" displayed and the return to the normal screen. Just keep holding until the code is displayed. My code on the back plate read 1112 and the display read 12 11

This date code display screen will automatically return to the normal settings screen.
Click to expand...

Glad to hear that. Just to let you know that mine is still working well so fingers crossed.

M
 
I've had the same problems with the faulty batch. As with other posters on this subject, a replacement is being sent out from the Netherlands. Can I ask those with experience in this area how easy, or not, is it to fit the new part?

Thank-you
 
Sponsored Links
Very simple, prodecure is as follows:-

Isolate power
Undo two screws on the bottom of the old programmer
Lift off programmer
Clip new programmer into place
Do the two screws up again
Restore power
 
I came across this post while looking for similar issues on my ST9420c My problems appear similar in nature, but the date code I get on the LCD is '2213' which if I understand some earlier posts correctly means it was made in 2013, week 22.

Are there still ongoing problems so far as anyone knows? I have emailed Honeywell in the mean time, but some back up stories may be helpful as I'm just outside 12 months after installation.

Thanks
 
My st9400c is outside the batch at 0939, and is not working. Works fine on auto but manual overrides don't turn on the relays unless I tap them (top rh corner). However I found that turning off the backlight gets it working again. I guess that there is only just enough power to set the two relays. To turn the light off, press - and ok for 8 seconds to enter set up mode and set parameter 2 to 0. It will exit after 10 minutes automatically, or just switch the run slider anywhere and back to run.
 
Thank you all! I have managed to fix my Honeywell ST9400C batch 1227 with your help. It was not part of the faulty batch but it was flashing and turning off when switched to once or const. Turning off the back light seems to have fixed it and it's now working again and underfloor heating has switched on.

Don't you just love the internet! Thanks again!
 
Does anyone know what the actual fault is caused by?

Tony
 
The voltage on the relay was 27v which dropped to 20v with both relays on. (19v and 15v if the backlight it's on as well). A working controller gave 45v with little change with load. An oscilloscope confirmed the low voltage with a ripple of 3v pp at about 100hz so looks like the zener bridge is OK. Then I removed the big blue Epcos 680nF emi suppression capacitor filter and that only read 180nF ie well outside the 10% tolerance. A new capacitor on eBay for £2 fixed the problem. Now it's all working again.
 
Last edited:
Purchased a new build house back in 2011, with the ST9400C already installed. Unfortunately became aware recently that the water was not very hot shortly after the timer had been on... So pressed the +1 hr option, and then I noticed that there was an issue...


Checked the serial number on the back, 1111, fell within the known faulty batch codes (1037 - 1139), so phoned Honeywell UK (01344 656200 option 1) this morning, was on hold 23 minutes to speak to someone, described the problem and was then quickly informed that they will be sending out a free replacement... I was asked if I had any proof of purchase, of which I do not being a new build, but was then informed that this was not important due to the serial number that I gave.

Thanks to previous comments for the help... Saved me quite a few quid. :)
 
Just like to say thanks to this thread for helping my with my st9400c issues! Recently moved into a house which has this model installed and there have been a few issues which we had put down to boiler. More recently had noticed that the unit was flashing on and off exactly like the video posted recently. Also as a result of this thread, I found out that my serial number falls within the 'dodgy batch' category. I have emailed honeywell and hopefully will get it sorted. As it turns out I'm only ten mins away from their head office so if no reply will just pop in lol finding out there was a dodgy batch was a lightbulb moment esp with the reduced voltage reported. Tested the wires into the boiler and low and behold only sending 15v, fingers crossed get a replacement :) will keep you updated and thanks again!
Quick vid of the issues
 
I went on the advice of Dce regarding the onboard capacitor, but for now I just turned off the backlight and it's been working since. In case it fails again I have the capacitor information so I can source one easily if needed.
Great thread, thanks all.
 
Just done similar to El Barto - turned off backlight and can now operate either HW relay OR CH relay (but not both at same time). My programmer falls within suspected batch so have emailed Honeywell requesting help/replacement as suspect item faulty. Will await their reply. If reply is negative I will replace capacitor (thanks for details Dce) and keep my fingers crossed. So pleased positive forums like this exist to assist in the solving of technical problems!
 
D

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
You must log in or register to reply here.
Sponsored Links

Similar threads

J
Programmer Horstman to Honeywell ST9400C
2 3
Replies
31
Views
1K
Jbenz
J
A
Replacing old Siemens thermostat with Honeywell THR870C
Replies
1
Views
8K
Adam42
A
J
Replacement of Landis & Gyr RWB2 + Honeywell T6060
Replies
3
Views
9K
mikely
M
R
HONEYWELL ST9400C & ST9500C:
2
Replies
15
Views
10K
stem
stem
S
Replace Pottorton EP6002 (Version no longer available)
Replies
4
Views
7K
sbarrick
S
Back
Top