Installation and Maintenance Manual

Diagnostics
48 GTND-SVX01B-EN
N. Fan will not stop. 1. Control board is in flame failure
mode.
1. Turn 115V power off to the unit, wait 10 seconds, and
reapply voltage to the unit.
2. Fan improperly wired. 2. Check wiring of fan circuit per wiring diagram.
3. Defective board. 3. If unit is not calling for heat and board is not in a flash code
mode, replace board.
O. Not enough heat. 1. Incorrect gas input. 1. Refer to “All Unit Sizes: Operation,” p. 39.
2. Heater undersized. 2. Is the heater output sized correctly for the heat loss of the
space? Has the space been enlarged?
3. Thermostat malfunction. 3. Check thermostat circuit, 24V at terminals “R” and “W” on
terminal strip.
4. Heater cycling on limit. 4. Check air movement across heat exchanger. Check voltage
and amps to fan motor. Check gas input to ensure unit is
not over-fired. Check heat exchanger to ensure unit is not
dirty.
5. Incorrect orifice size(s). 5. Check orifice size; replace if undersized.
P. Too much heat. 1. Unit is over-fired. 1. Refer to “All Unit Sizes: Operation,” p. 39. Check orifice size;
if too big, replace.
2. Thermostat malfunction. 2. Check thermostat for operation, to ensure circuit opens and
closes.
3. Heater runs continuously. 3. Check wiring per diagrams; check operation at gas valve.
Look for short (such as staples piercing thermostat wiring)
in thermostat circuit and correct.
Q. Blown fuse. 1. Electrical short. 1. Refer to wiring diagram.
2. Improper ground. 2. Check grounding wires.
3. Defective gas valve. 3. Replace.
R. Cold air is delivered during heater
operation.
1. Incorrect manifold pressure or
input.
1. Refer to “All Unit Sizes: Operation,” p. 39.
S. Hi-Limit switch tripping. 1. Unit is overfiring. 1. Burner orifice(s) may be too large: verify/replace if
required.
2. Air flow too low. 2. Check for proper voltage. Ensure fan blade is correctly
positioned 1/3 inside venturi.
3. Defective switch. 3. Check operation of switch. Did the switch open when unit is
running or is the switch open during start-up?
4. Defective control board. 4. Check for 24V on line side of the high limit. Constant voltage
should be recorded; if not, control board is suspect. Check
flash code.
T. Power venter will not run. 1. Loose wiring or connections. 1. Check all wiring in the power vent circuit to ensure good
connection, including “Neutral”.
2. Motor overload is tripped or bad
motor.
2. Check for 115V between motor leads and check amp draw
of motor. Replace if needed.
3. Defective control board. 3. Check for continuous 115V on terminal “CBM Blower” and
neutral during call for heat. If not present and all checks are
normal, replace.
U. Power venter motor turns on and
off while burner is operating.
1. Power venter improperly wired. 1. Check power venter circuit per wiring diagram.
2. Motor overload cycling or
defective motor.
2. Check motor amps against motor name plate rating, check
voltage; replace motor if defective.
3. Defective control board. 3. Check for continuous 115V on terminal “CMB Blower” during
call for heat; replace board if found defective.
V. Power venter motor will not stop. 1. Power venter improperly wired. 1. Check power venter circuit per wiring diagram.
2. Main burner not lighting while
thermostat calls for heat.
2. Heater is in lockout mode; check flash code table for
problem.
3. Defective control board. 3. No flash codes present along with no call for heat; replace
control board.
4. Loss of pressure. Pressure switch
not made.
4. Check venting for blockage. Check tubing for blockage or
hole. Check spud for blockage.
Table 11. Troubleshooting guide (continued)
Symptoms Possible Cause(s) Corrective Action