Troubleshooting Guide - Honeywell Y9420S User Manual

Can I override the Programmer from the DT92E thermostat?
As well as changing the set temperature from the DT92E, it is also possible to override
the heating system on or off from the DT92E. This is only possible if the ST9420C is in
AUTO or ONCE Modes. If ST9420C is in CONT mode it will not be possible to switch
the heating off from the DT92E. Similarly, if ST9420C is in OFF mode, it will not be
possible to switch the heating on from the DT92E. If these latter overrides are required
it is first necessary to change the ST9420C mode setting to AUTO or ONCE.

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:
FAQ AND TROUBLESHOOTING
Possible Cause
No power to the
heating system.
Fault in ST9420C
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.
Remedy
Check that there is power to the
heating system.
Call Installer
Check that the temperature
controls 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.
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