Carrier 58MVP Error Code 31: High-Heat Pressure Switch or Relay Did Not Close or Reopened
What Does Code 31 Mean?
Status code 31 on the Carrier 58MVP means the high-heat pressure switch input failed to close on a call for high-heat, or opened during high-heat operation. Carrier's guide adds that the control relay may be defective or the gas valve mis-wired, and cross-references code 32 (the low-heat pressure switch failing to close or reopening).
The pressure switch proves that the inducer is producing enough draft to safely vent combustion gases. On this variable-capacity furnace the high-heat stage moves more combustion air, so it uses a dedicated high-heat pressure switch; if venting is restricted or the inducer is weak, the switch cannot close, or drops out, specifically at high fire. The most common physical causes are a blocked or restricted exhaust vent and a failing inducer motor.
Diagnosing the pressure switch, inducer, venting, control relay, and gas-valve wiring is professional work — it involves combustion safety and is not a DIY repair.
What You'll Notice
- The furnace fails to run on high heat, or drops out shortly after going to high fire
- The board LED flashes code 31
- Weak or short heating cycles, especially on cold days when high heat is demanded
- Possible signs of a blocked exhaust or intake vent (debris, snow, or nesting at the termination)
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Blocked or restricted exhaust vent | Most common | ✗ Call a pro → |
How This Is Diagnosed
A technician checks the exhaust and intake for blockage, measures inducer performance and draft, and tests whether the high-heat pressure switch closes at its rated pressure. If venting and the inducer are good, they check the control relay and the gas-valve wiring against the diagram. This is combustion-safety work performed by a professional.
When to Call a Professional
This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:
- The furnace will not run on high heat or drops out at high fire
- The exhaust or intake termination looks blocked by debris, snow, or nests
- The board repeatedly flashes code 31
- The problem followed recent service to the gas valve or control board
Frequently Asked Questions
What's the difference between code 31 and code 32 on a 58MVP?
Code 31 is the high-heat pressure switch failing to close or reopening; code 32 is the low-heat pressure switch failing to close or reopening. Both prove venting, but for different heating stages.
Can a blocked vent cause code 31?
Yes — a restricted or blocked exhaust vent is a common cause, since the high-heat pressure switch cannot close if draft is inadequate at high fire.
Sources
✓ Verified against manufacturer service manual — March 2026