Flame pops back. | Burner orifice too small. | Check with local gas supplier for proper orifice size and replace. |
Noisy flame. | Irregular orifice causing whistle or resonance. | Replace orifice. |
| Excessive gas input. | Test and reset manifold pressure |
Yellow tip flame. | Clogged main burners. | Clean main burner ports. |
Note: Some yellow tipping on LP gas is permissible. | Misaligned orifices. | Replace manifold assembly. |
| Insufficient combustion air. | |
| Unit possibly over fired. | Check gas input and manifold pressures. |
| Partially blocked flue vent pipe. | Check flue vent pipe and clear as needed. |
Floating flame. | Blocked venting. |
| Insufficient combustion air. | Check combustion air inlet openings and/or vent pipe and clear as needed. |
| Blocked heat exchanger. | Clean heat exchanger. |
| Air leak into combustion chamber or flue collector. | Check flue collector and clear as needed. |
Gas odor. | Gas leak. Shut off gas supply immediately! | Inspect all gas piping and repair accordingly. |
Shut off gas supply immediately! | Leaking gas test port on valve. | Check to ensure gas test ports are sealed. |
| Blocked heat exchanger. | Clean heat exchanger. |
| Blocked flue collector. | Check flue collector and clear as needed. |
| Negative pressure in the building. | |
Delayed ignition. | Improper ground. | Check grounding wires and spark ignitor connections. |
| Bad or broken spark cable. | Inspect spark cable connections andcuts. Replace if necessary. |
| Faulty control board. | Check to ensure spark ignitor is energized after pre-purge period. |
| Pressure regulator set too low. | Test and reset manifold pressure |
| Main burner orifices dirty. | Clean or replace orifices. |
| Improper venting. | |
Failure to ignite. | Gas leak. Shut off gas supply immediately! | Open all manual valves, check for leaks. Inspect all gas piping and repair accordingly. |
| No power supply to the unit. | Turn on power supply, check fuses and replace if bad. |
| Thermostat not calling. | Turn up thermostat. Check for 24 V on terminals R and W1 on terminal strip. |
| Defective high limit switch. | Check switch for continuity if open with no heat present; replace. |
| Defective air pressure switch. | Check switch operation to ensure switch closes after power vent purge period. If it does not make, check tubing connections for blockage. |
| Defective spark ignitor, gas valve, thermostat or transformer. | Check for continuity and voltage in safety and control circuits; replace an item where continuity or voltage not found. |
| Loose wiring. | Check all wiring per diagram. |
| Improper ground. | Check all ground wires and connections. |
| Improper thermostat or transformer wiring. | Check both for wiring according to diagram. |
Condensation. | Improper venting. | |
| Unit under fired. | Check gas supply pressures to the unit. |
| Building/space too cold. | A minimum of 50°F (10°C) thermostat setting must be maintained to deter formation of condensation. |
Burners will not shut off. | Thermostat located improperly. | Relocate thermostat away from outside wall or drafts. |
| Improper thermostat wiring. | Check thermostat circuit for open and close on heater terminal strip K R" and W W." |
| Shorted circuit. | Check thermostat circuit for shorts or any staples piercing wires. |
| Defective thermostat. | If thermostat is calling after set point has been satisfied, replace. |
| Defective/sticking gas valve. | Check for 24 V on gas valve terminals when thermostat not calling. Replace if necessary. |
| Defective control board. | Check for 24 V at terminals "R" and "W." If not present and board is not in flash code mode, replace board. |
| Excessive gas supply pressure. | |
Rapid burner cycling. | Loose electrical connections at thermostat or gas valve. | Tighten all electrical connections. |
| Unit cycling on high limit. | Check for proper air supply across heat exchanger and proper gas supply. |
| Thermostat located improperly. | Relocate thermostat away from outside wall or drafts. |
| Defective high limit switch. | Jumper high limit switch wiring (orange and yellow wires). If burner operating normally, replace switch. |
Not enough heat. | Incorrect gas input. | |
| Unit undersized. | Is the unit output sized correctly for the heat loss of the space? Has the space been enlarged? Is the unit located in the space properly |
| Thermostat malfunction. | Check thermostat circuit; 24 V on terminals "R" and "W" on terminal strip. |
| Unit cycling on high limit. | Check air movement across the heat exchanger. Check gas input to ensure unit is not over fired. Check heat exchanger to ensure unit is not dirty. |