Fault Code 31
HIGH-PRESSURE SWITCH FAULTÐThis fault can occur under the scenarios shown below, keep in mind that whenever furnace control board shuts unit down, gas shuts off immediately, inducer continues running for 15 sec, and if blower is running, it remains running at low-heat speed or reduces to low-heat speed for selected off delay.
·CALL FOR HEATÐIf high-pressure switch HPS is made when a call for heat is initiated, furnace control board flashes Fault Code 31 until switch opens, then cycle begins.
·LOW HEAT
1.PREPURGE AND FIRST 45 SEC AFTER IGNITIONÐIf high-pressure switch HPS makes during prepurge or just after ignition, furnace control board continues operating until burners are lit and inducer RPM is within 10% of calculated low-fire RPM. If high-pressure switch HPS remains made, furnace control board starts flashing Fault Code 31, shuts unit down, waits 2 minutes, stops flashing Fault Code 31, and restarts heating cycle.
2.STEADY-STATEÐIf high-pressure switch HPS makes during low heat, furnace control board starts flashing Fault Code 31, shuts unit down, waits 2 minutes, stops flashing Fault Code 31, and restarts heating cycle.
·HIGH HEAT
1.PREPURGEÐIf high-pressure switch HPS does not make within 45 sec after low-pressure switch LPS makes, furnace control board starts flashing Fault Code 31, shuts unit down, waits 2 minutes, stops flashing Fault Code 31, and restarts heating cycle.
If high-pressure switch HPS opens before ignition, furnace control board starts flashing Fault Code 31 and ramps inducer RPM up until high-pressure switch HPS remakes. When high-pressure switch HPS remakes, furnace control board stops flashing Fault Code 31 and continues heating cycle. If high-pressure switch HPS does not remake within 45 sec after opening, furnace control board continues flashing Fault Code 31, shuts unit down, waits 2 minutes, stops flashing Fault Code 31, and restarts heating cycle.
2.FIRST MINUTE AFTER IGNITIONÐIf high-pressure switch HPS opens during first minute after ignition, furnace control board starts flashing Fault Code 31, shuts unit down, waits 2 minutes, stops flashing Fault Code 31, and restarts heating cycle.
3.STEADY-STATEÐIf high-pressure switch HPS opens during high heat, furnace control board starts flashing Fault Code 31 and ramps inducer RPM up until high-pressure switch HPS remakes. When high-pressure switch HPS remakes, furnace control board stops flashing Fault Code 31 and continues heating cycle. If high-pressure switch HPS does not remake within 45 sec after opening, furnace control board continues flashing Fault Code 31, shuts unit down, waits 2 minutes, stops flashing Fault Code 31, and restarts heating cycle.
4.HIGH FIRE TO LOW FIRE TRANSITIONÐWhen using a 2-stage thermostat and W2 is de-energized, high-pressure switch HPS must open within 45 sec. If high-pressure switch HPS does not open within 45 sec after W2 was de-energized, furnace control board starts flashing Fault Code 31, shuts unit down, waits 2 minutes, stops flashing Fault Code 31, and restarts heating cycle.
| STEP | ACTION | YES | NO | GO TO |
| 1. | Turn power off, remove blower access panel, and disconnect R thermostat lead. | Ð | Ð | 2 |
| 2. | Turn power on and depress door switch. Use a piece of tape to hold switch closed. | Ð | Ð | 3 |
| 3. | Jumper R and W/W1 thermostat terminals on furnace control board. | Ð | Ð | 4 |
| 4. | Observe operation of furnace through 1 heating cycle. | Ð | Ð | 5 |
| 5. | Does fault occur again? | 9 | 6 | Ð |
| 6. | Does a different fault occur? | 7 | 8 | Ð |
| 7. | Go to page number indicated in Index for fault code flashed. | Ð | Ð | INDEX |
| 8. | Go to page number indicated in Index for CLEANUP AND START-UP INSTRUCTIONS. | Ð | Ð | INDEX |
| 9. | Does fault occur within 5 sec after W/W1 is energized? | 10 | 18 | Ð |
| 10. | Do you have 24v between the N.O. (Normally Open) contact on high-pressure switch HPS and Com | 12 | 15 | Ð |
| on furnace control board? |
| | | | |
| 11. | Replace furnace control board. | Ð | Ð | 8 |
| 12. | Is high-pressure switch HPS wired correctly? | 14 | 13 | Ð |
| 13. | Rewire high-pressure switch HPS per wiring diagram. | Ð | Ð | 8 |
| 14. | Replace pressure switch assembly. | Ð | Ð | 8 |
| 15. | Do you have 24v between connector terminal PL2-4 and Com on furnace control board? | 16 | 11 | Ð |
| 16. | The main harness is miswired. | Ð | Ð | 17 |
| 17. | Fix problem. | Ð | Ð | 8 |
| 18. | Does fault occur during blower on delay period? | 19 | 23 | |
| 19. | Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals. | Ð | Ð | 20 |
| 20. | Turn power on and wait several sec, then jumper R, W/W1, and W2 thermostat terminals on fur- | Ð | Ð | 21 |
| nace control board. |
| | | | |
| 21. | Does Fault Code 14 start flashing when high-pressure switch HPS makes? | 22 | 14 | Ð |
| 22. | The BLUE and GREEN wires to gas valve GV are reversed. | Ð | Ð | 17 |
| 23. | Does fault occur during low fire after blower turns on? | 24 | 29 | Ð |
| 24. | Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals. | Ð | Ð | 25 |
