Troubleshooting Guide - Honeywell Home ST9420C User Manual

Troubleshooting Guide

This is a quick guide to help you diagnose and cope with possible problems with
your wireless control system. For further assistance, please contact your Installer.
Symptom
ST9420C has a blank
LCD display
ST9420C indicates
that Heating and/or
Hot Water are ON, but
radiators are cold and/
or taps are running
with cold water.
ST9420C shows the
message:
'INTERNAL FAULT'
Every few seconds,
the ST9420C screen
shows the message:
Although the heating
is still operating, the
ST9420C screen keeps
flashing the message:
The ST9420C screen
shows the message:
Possible Cause
No power to the
heating system
Fault in ST9420C
Temperature controls Check that the temperature controls
are switched off or
set too low
Boiler or other
system controls
have malfunctioned
Fault in ST9420C
ST9420C is
counting down the
number of days
until your next boiler
service is due.
Your boiler service
is overdue.
Your boiler service
is overdue and
the boiler has
been automatically
switched off to
ensure your safety.
FAQ AND TROUBLESHOOTING
Remedy
Check that there is power to the
heating system
Call Installer
in the system are set to appropriate
levels
Call Installer
Call Installer
Arrange a boiler service before the
counter reaches zero.
After servicing your boiler, the Service
Engineer / Installer will reset the
ST9420C to remind you when the next
boiler service is due. Each service is
normally a maximum of 1 year apart.
Arrange an immediate boiler service.
After servicing your boiler, the Service
Engineer / Installer will reset the
ST9420C to remind you when the next
boiler service is due. Each service is
normally a maximum of 1 year apart.
Arrange an immediate boiler service.
If set to do so, it may be possible to
obtain limited use of the boiler by
pressing any EXTRA HOUR button.
Each button press will allow operation
of the boiler for 1 hour at a time, and
the screen will display the message
'On 1h'.
After servicing your boiler, the Service
Engineer / Installer will reset the
ST9420C to remind you when the next
boiler service is due. Each service is
normally a maximum of 1 year apart.
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