Carrier · Status code
Carrier 59TP7A status code 43.1: HPS closed before LPS
Status code 43.1 means the high-heat (secondary) pressure switch HPS closed before the low-heat (main) pressure switch LPS during the start-up sequence. On the 59TP7A the control expects the main switch to prove draft first; the secondary switch closing out of sequence is reported as 43.1.
Smell gas?
- Do not operate light switches, appliances or phones inside.
- Leave the building and leave the door open behind you.
- From outside, call the FortisBC emergency line at 1-800-663-9911 or 911.
- Only after that, call BC Wide about the furnace.
A furnace that will not run is a breakdown, not a gas emergency. Gas smell, a CO alarm, soot or scorching are.
On the control
- Code
- 43
- Minor
- 43.1
- Door LED
- 4 short flashes then 3 long
- Controller
- 59TP7A integrated furnace control with 3-digit LCD display and door LED
- Applies to
- Carrier Performance 97 (59TP7A)
- Manual
- 59TP7A-01SI
What each minor code says, verbatim
| Display | Manufacturer wording |
|---|---|
| 43.1 | HPS closed before LPS |
A code is a condition, not a diagnosis
An out-of-sequence switch reading usually means a hose or port problem: the HPS hose connected to the wrong port, a blocked LPS port or hose, water in one sensing line, or a switch whose set-point does not match the family. The switches and their hoses are tested with a manometer; the sequence is verified across a full start-up before anything is replaced.
Which furnaces this applies to
Documented for Carrier 59TP7A furnaces (all nine sizes) in installation instructions 59TP7A-01SI REV A, edition 06/23. The pressure switches are labelled COLLECTOR BOX-LPS and HOUSING-HPS; each has its nominal break point printed on the switch label.
Scope: Carrier 59TP7A Performance 97 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, including any minor digit (for example 33.2), and write it down.
- Look, without touching, for obvious conditions you can report: snow or ice at the vent terminations, water on the floor, a loaded filter, a condensate pump that is full or off.
- Note whether the furnace still heats at all, and how long it runs before the code returns.
- Note whether the code appears every call or only after service work on the furnace.
- Check the floor for water and the vent terminations for blockage.
Do not
- Do not bypass or jumper the door switch, limit switches, rollout switches or pressure switches.
- Do not open the burner compartment, disconnect tubing, or adjust the gas valve or gas pressure.
- Do not keep cycling power to force the furnace to relight; repeated resets hide the fault and can allow unburned gas to build up after ignition failures. If the code returns, stop and call.
Homeowner-safe checks (look and read only)
- Note whether the code appears every call or only after service work
- Check the floor around the furnace for water
When to call a technician
- If the furnace is not heating
What a technician does
- A technician verifies the hose routing against the installation instructions, tests both switches with a manometer against their printed set-points, and confirms the correct start-up sequence before clearing the fault.
Related components and symptoms
Questions people ask
I just had service done and now 43.1 shows. What happened?
A hose reconnected to the wrong port or a trap reinstalled incorrectly is a common cause of out-of-sequence switch readings after service. Ask the technician to verify the hose routing first.
Seeing code 43 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.