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UHD LOW PROFILE DUCT FURNACE INSTALLATION OPERATION AND SERVICE MANUAL
30 of 47
Figure 17: Manual Reset Limit Switch
12.3 Lighting Instructions
12.3.1 To Turn On Heater
1. E n s ure that the electrical and gas supplies to
the heater are on. Check that the on site
controls are "ON".
IMPORTANT: The thermostat setting must be above
the ambient temperature for the heater to operate.
2. The automatic firing sequence will begin as
described on Page 27, Figure 15. The heater
will now operate automatically under the control
of the on site controls.
12.3.2 To Turn Heater Off
Set the thermostat to the "OFF" position.
The burner will turn off immediately.
To restar t, turn the thermostat above room
temperature.
12.4 Simple Troubleshooting
Some possible reasons for the heater not operating
are:
1. Ga s s upply not "ON".
2. Electricity supply not "ON".
3. The time and/or temperature controls are not
"ON".
4. A limit switch may have operated. This may be
caused by an interruption of the electrical
supply, failure of the distribution fan or vent or
heat exchanger blockage.
If a temperature limit switch persistently trips, there
is a fault which must be investigated by a contractor
qualified in the installation and service of gas-fired
heating equipment.
12.4.1 Simple Troubleshooting (Burner Faults)
If the burner fails to ignite for any reason, it will retry
for ignition (four trials total). After four unsuccessful
ignition trials, the control will put the heater into
lockout for one hour.
Lockout should not occur during normal operation of
the heater and indicates there is a fault condition
which must be corrected. There is an LED light on
the ignition control that flashes codes to assist in
fault correction. See Page 30, Figure 18 for LED
indication codes.
Figure 18: LED Diagnostic Codes
Reset Button
To reset manual reset limit switch, press reset
button. NOTE: To reset, the switch must be cool.
Description Part Number
Manual Reset Limit Switch 90412106
LED INDICATION FAULT MODE
Slow Flash Normal Operation - No call for heat.
Fast Flash Normal Operation - Call for heat.
2 Flashes Ignition Lockout - No flame detected.
3 Flashes Airflow Fault - Pressure switch open or closed.
4 Flashes Temperature Limit or
Manual Reset Limit Switch Open
5 Flashes Flame Sense Error - Gas valve not energized.
Steady On Internal Control Failure