Here's a link to the manual. You'll probably need it for future and current issues.
https://www.google.com/search?q=Honeywell+ST9400S+manual&ie=utf-8&oe=utf-8&client=firefox-b-1-ab
Resetting the Service Timer Function
If the Service Timer function is enabled you will be required to reset it after the boiler service has been carried out.
The process for resetting the Service Timer is as follows:
a. Enter Installer Modes (as described on page 3 see manual) and navigate to SET SERVICE mode. In response to the query 'SET SERVICE OK ?' press the button to enter SET SERVICE mode.
b. If you no longer require the Service Timer, disable it by setting parameter AL to 0 and confirm with the button.
c. If you still require the Service Timer, set the number of days until the next service is due using parameter d and confirm with the button.
d. Whilst in SET SERVICE mode, use the opportunity to change any other service parameters if required.
e. Exit by moving the slider to the next position and back again to RUN
My suggestion is to download the manual and print a hard copy to have when you begin the reset process.
I know i'd need it! :)
Cheers
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