Carrier · Status code
Carrier 59TP6C status code 31: high-heat pressure switch (HPS) open or slow to close
On the 59TP6C control, major code 31 refers to the high-heat (secondary) pressure switch, HPS. Carrier's service label lists two minor codes: 31.6 "Open secondary pressure switch (HPS)" and 31.7 "High Heat Only for next cycle – HPS failed to close in 75s when transitioning from low to high heat". The related low-heat (main) pressure switch has its own code, 32.2 "Open Main pressure switch (LPS)", and 23.5 covers "HPS stuck closed".
On the control
- Code
- 31
- Minor
- 31.6 · 31.7
- Door LED
- 3 short flashes then 1 long
- Controller
- 59TP6C integrated furnace control with 3-digit LCD display and door LED
- Applies to
- Carrier Performance 96 (59TP6C)
- Manual
- 59TP6C-01SI REV A
What each minor code says, verbatim
| Display | Manufacturer wording |
|---|---|
| 31.6 | Open secondary pressure switch (HPS) |
| 31.7 | High Heat Only for next cycle – HPS failed to close in 75s when transitioning from low to high heat |
A code is a condition, not a diagnosis
A pressure-switch code tells you the control did not see the switch close (or saw it open) when it expected to; it does not tell you which part failed. The same code results from a blocked or frozen vent or intake, a flooded condensate trap or drain, a kinked or split pressure-switch hose, an inducer that is not reaching speed, a restricted heat exchanger, or a failed switch. Only testing on site with a manometer and inspection of the venting and condensate path can distinguish these.
Which furnaces this applies to
Documented for Carrier 59TP6C furnaces (all nine sizes) in installation instructions 59TP6C-01SI REV A, edition 06/23. Earlier 59TP6A and 59TP6B furnaces use a different control and LED-only code display; their code 31 definition must be read from their own manuals and is not assumed here. Bryant and Payne furnaces built on similar platforms are documented separately when their records are added.
Scope: Carrier 59TP6C Performance 96 furnaces with the on-board 3-digit display control. Not sure which control you have? Send us the full model number from the rating plate.
Safe things to look at first
- Read the full code on the control display through the door: 31.6 and 31.7 mean different things.
- Note whether the furnace still heats on low fire (31.7 lets it finish the cycle in low heat) or has stopped heating.
- Look outside at the vent and air-intake terminations for snow, ice, leaves or a nest. Do not remove anything from the pipes; just note what you see.
- Look, without touching, for water on the floor around the furnace or at the condensate trap and drain, and for a condensate pump that is full or not running.
- Check that the furnace filter is not heavily loaded and note when it was last changed.
Do not
- Do not jumper or bypass the pressure switch, the limit switch or the door switch.
- Do not disconnect hoses, open the burner compartment or adjust the gas valve.
- Do not keep cycling power to force the furnace to relight; if the code returns, stop and call.
Homeowner-safe checks (look and read only)
- Check the vent and intake terminations for snow, ice, leaves or a nest
- Check the floor around the furnace for water
- Note whether the inducer runs when the thermostat calls
When to call a technician
- If the furnace is not heating
- If the code appears on every call
Also documented on the same controller family: Carrier Performance 97 (59TP7A).
What a technician does
- A technician measures the actual pressure at the switch with a manometer against Carrier's switch set-point and checks the inducer at both speeds.
- The condensate trap, drain and collector-box ports are cleaned and the trap orientation checked for the installed position.
- Vent and combustion-air pipes are inspected for total equivalent length, slope, sagging, blockage and termination clearance.
- The pressure-switch hoses and the switch itself are tested and replaced only if they fail, and the fault history on the control is cleared after the repair is verified.
Related components and symptoms
Questions people ask
My furnace shows 31 but still heats. Do I need a repair?
If the display shows 31.7, the control has fallen back to low heat for the cycle because the high-heat pressure switch was slow to close. The furnace keeps running but the cause, often a partial vent or condensate restriction, should be found before it becomes a no-heat call.
Can I clear code 31 by turning the furnace off and on?
Cycling power clears the display, not the cause. Carrier's control also stores the last seven faults, which a technician uses for diagnosis, so it is better to note the code and call than to reset repeatedly.
Is code 31 the same on my older Carrier furnace?
Not necessarily. The 59TP6C's code table is specific to its control. If your rating plate shows 59TP6A, 59TP6B or a different family, the meaning must be read from that furnace's own manual. Tell us the full model number and we will check.
Is a pressure-switch fault dangerous?
The switch is a safety device that stops the burner when the control cannot prove the inducer is moving combustion air. A code 31 lockout is the furnace protecting itself. If you ever smell gas or a CO alarm sounds, leave and call FortisBC at 1-800-663-9911 or 911 before anything else.
Seeing code 31 on your Carrier?
Tell us the full code, the model number and whether the furnace still heats on low. BC Wide prioritizes no-heat calls across Greater Vancouver.