Honeywell DT92E User Manual

29
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 Possible Cause Remedy
ST9420C has a blank LCD
display
No power to the
heating system.
Check that there is power to the
heating system.
Fault in ST9420C Call Installer
ST9420C indicates that
Heating and/or Hot Water
are ON, but radiators are
cold and/or taps are running
with cold water.
Temperature controls
are switched off or
set too low.
Check that the temperature
controls in the system are set to
appropriate levels.
Boiler or other
system controls
have malfunctioned.
Call Installer
ST9420C shows the
message:
‘INTERNAL FAULT’
Fault in ST9420C Call Installer
Every few seconds, the
ST9420C screen shows the
message:
ST9420C is
counting down the
number of days
until your next boiler
service is due.
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.
Although the heating is still
operating, the ST9420C
screen keeps flashing the
message:
Your boiler service
is overdue.
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.
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.
FAQ AND TROUBLESHOOTING

Honeywell DT92E Specifications

General

Display	LCD
Power Supply	2 x AA batteries
Temperature Range	5°C to 35°C
Mounting	Wall-mounted
Switching Current	3 A
Switching Voltage	230 V AC
Backlight	No
Type	Digital Room Thermostat
Compatibility	Heating systems
Dimensions	92 x 92 x 27 mm
Weight	150g
Control Mode	TPI (Time Proportional Integral)