Maintenance Manual

Diagnostics
GMND-SVX01B-EN 37
2. Pilot adjustment screw turned too
low on combination main gas
valve.
2. Increase size of pilot flame. Refer to “Operation,” p. 26.
3. Air in gas line. 3. Purge air from line.
4. Incorrect lighting procedure. 4. Follow lighting instruction label adjacent to gas valve.
5. Dirt in pilot orifice. 5. Remove pilot orifice. Clean with compressed air or solvent.
(Do not ream.)
6. Extremely high or low gas
pressure.
6. Refer to “Operation,” p. 26.
7. Drafts around unit. 7. Eliminate drafts. Refer to “Installation: Mechanical,” p. 12.
8. Pilot valve not opening (faulty
wiring).
8. Inspect and correct all wiring.
9. No spark (faulty wiring). 9. Inspect and correct ignition system wiring. See symptoms
U, V, and W.
10. Defective gas valve. 10. Replace gas valve.
N. Power venter will not run. 1. Loose wiring. 1. Check and tighten all wiring connections per diagrams.
Thermostat wires tagged “W” and “G” must be connected
together (unless special thermostats are used; if so, see
thermostat wiring diagram, “Electrical Connections,” p. 24).
2. Defective motor overload
protector or defective motor.
2. Replace motor.
3. Defective power venter relay. 3. Check for 24V across terminals on fan relay. If 24V is
present, jumper terminals numbered 2 and 4. If motor runs,
the fan relay is defective and must be replaced. If 24V is not
present, check wiring per diagrams.
O. Power venter motor turns on and
off while burners are operating.
1. Fan relay heater element
improperly wired.
1. Be sure venter relay heater terminals are connected per
diagrams.
2. Defective venter relay switch. 2. Replace venter relay.
3. Motor protector cycling on and off. 3. Check motor amps against motor name plate rating, check
voltage, replace venter relay motor if defective.
4. Motor not properly oiled. 4. Refer to label on motor.
P. Power venter motor will not stop. 1. Improperly wired venter relay. 1. Check all wiring.
2. Main burners not lighting while
thermostat calls for heat.
2. Refer to H and N symptoms.
3. Defective venter relay. 3. Replace venter relay.
Q. Not enough heat. 1. Incorrect gas input. 1. Refer to “Operation,” p. 26.
2. Heater undersized. 2. This is especially true when the heated space is enlarged.
Have the heat loss calculated and compare to the heater
output (80 percent of input). Your gas supplier or installer
can furnish this information. If heater is undersized, add
additional heaters.
3. Thermostat malfunction. 3. Replace thermostat.
4. Heater cycling on high limit. 4. Check air movement through heat exchanger. Check
voltage to fan motor. Clean power venter motor.
5. Check outside dampers if used. 5. Adjust dampers accordingly.
R. Too much heat. 1. Thermostat malfunction. 1. Replace thermostat.
2. Heater runs continuously. 2. Check wiring per diagrams; check operation at valve. Look
for short (such as staples piercing thermostat wiring), and
correct; replace gas valve. Refer to “Operation,” p. 26.
S. Cold air is delivered on start up. 1. Fan relay heater element
improperly wired.
1. Be sure fan relay heater terminals are connected per
diagrams.
T. Cold air is delivered during heater
operation.
1. Incorrect manifold pressure or
input.
1. Refer to “Operation,” p. 26.
2. Voltage to unit too high. 2. Check motor voltage with fan running. Should be 115 volts
AC.
3. Air throughput too high. 3. Refer to “Operation,” p. 26.
Table 8. Troubleshooting guide (continued)
Symptoms Possible Cause(s) Corrective Action