Installation and Maintenance Manual

Diagnostics
GTND-SVX01B-EN 49
1. Check the system thermostat to make sure it is calling
for heat. (Do not cycle the thermostat on and off at this
time.)
2. Remove the access panel. Do not interrupt power to
the control board by opening any electrically
interlocked panels.
3. Observe the LED indicator on
the control board (a
green LED labeled “OK” indicates system faults); check
and repair system as noted in the chart to the right.
Note: Air flow proving switch and power venter hose
barbs must be free of any dust or debris at all times.
Periodically check these openings and/or if any
problems occur.
WARNING
Live Electrical Components!
During installation, testing, servicing and
troubleshooting of this product, it may be necessary to
work with live electrical components. Have a qualified
licensed electrician or other individual who has been
properly trained in handling live electrical components
perform these tasks. Failure to follow all electrical
safety precautions when exposed to live electrical
components could result in death or serious injury.
Table 23. All unit sizes: Troubleshooting with LED
Indicator Assistance for UT Control Board
LED Status Indicates Check/Repair
Slow Flash Control OK, no call
for heat.
Not Applicable
Fast Flash Control OK, call
for heat present.
Not Applicable
Steady Off Internal control
fault, or no power.
1. Line voltage on terminals
120 and C on transformer.
2. Low voltage (24V) on
terminals 24 and C on
transformer.
3. 5 Amp fuse on circuit board.
Steady On Control internal
failure or bad
ground.
1. Common side of
transformer grounded to
chassis.
2. Loose spark ignitor.
2 Flashes In lockout from
failed ignitions or
flame losses.
1. Gas supply off or gas supply
pressure too low.
2. Flame sense rod
contaminated or loose wire.
3. Gas valve switch is off or
wires are not connected.
4. Broken or cracked porcelain
on flame probe or spark
ignitor.
3 Flashes Pressure Switch
open with inducer
on or closed with
inducer off.
1. Obstructions or restrictions
in appliance air intake or
flue outlet are preventing
proper combustion airflow.
2. Moisture or debris in tubing
that connects pressure
switch and draft inducer.
3. Airflow switch jumpered or
miswired.
4 Flashes Limit or rollout
switch is open.
1. Open manual reset rollout
switch.
2. Gas pressure too high, over
fire condition.
3. Incorrect airflow due to
blockage or motor not
operating.
5 Flashes Flame sensed
while gas valve is
off.
1. Flame probe miswired or
shortened.
6 Flashes On-board
microprocessors
disagree.
1. Thermostat is interfering
with control board.