Carrier 58MVC Error Code 31: Medium-Heat Pressure Switch or HPSR Relay Did Not Close or Reopened
What Does Code 31 Mean?
Status code 31 on the Carrier 58MVC indicates that the medium-heat pressure switch input did not close when the furnace called for medium or high heat, or it opened unexpectedly during operation. The 58MVC is a step-modulating furnace that uses multiple pressure switches to verify safe venting at different heating stages.
When the medium-heat pressure switch fails to respond correctly, the furnace cannot confirm that the inducer is creating sufficient draft for the higher firing rates. This can be caused by a defective control relay that is not properly energizing the inducer to the correct speed, or by a gas valve that is mis-wired, causing the pressure switch circuit to behave incorrectly.
If this condition persists, the furnace will escalate to status code 32. A technician needs to test the medium-heat pressure switch, verify the inducer motor is running at the correct speed for medium heat, check the control relay operation, and inspect the gas valve wiring to ensure it matches the furnace wiring diagram.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Defective control relay | Common | ✗ Call a pro → |
| Gas valve mis-wired | Common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- When this code appears — diagnosing pressure switch and relay issues on a multi-stage furnace requires professional testing and possibly component replacement
✓ Verified against manufacturer service manual — March 2026