Carrier furnace code 31: High-Heat Switch or Relay Did Not Close or Reopened
Try DIY first, then call a pro
What does code 31 mean on a Carrier 58MVP, 58MVB or 58UVB furnace? On this two-stage variable-speed control, code 31 means the high-heat pressure switch didn't close on a call for high heat, or opened during high heat. Carrier's guide adds that the control relay may be defective or the gas valve miswired, and points to code 32. After a shutdown, the control either retries in 2 minutes or limits the next cycle to high heat, depending on when the fault happened. If the switch closes during low heat instead, the control flashes 31 and moves up to high heat. Single-stage 58STA and 58STX furnaces use code 31 for a different fault.
Before you touch anything: the six signs that mean stop troubleshooting and call a pro →
GOOD NEWS: THE FIRST CHECKS ARE FREE AND TAKE MINUTES.
Try these first — in this order
From ground level, look at the outdoor intake and exhaust ends for frost, snow or debris.
Pressure-drop measurement across the heat exchangers, inducer checks, and gas valve wiring. DIY part cost: $30–60 — a pro visit for this class of fault typically runs $150–350.
What causes it (in order of likelihood)
- Sagging vent pipe, or a clogged condensate drain trap or line TECH
- Restriction in the combustion-air or vent pipe, or frost on the combustion-air inlet DIY-CHECKABLE
- Failed pressure switch assembly or inducer motor TECH
- Defective control relay or miswired gas valve TECH
Parts referenced by this code
Always match parts against your model's parts list — part numbers vary within a series.
Questions about this code
What does code 31 mean on a Carrier 58MVP, 58MVB or 58UVB furnace?
On this two-stage variable-speed control, code 31 means the high-heat pressure switch didn't close on a call for high heat, or opened during high heat. Carrier's guide adds that the control relay may be defective or the gas valve miswired, and points to code 32. After a shutdown, the control either retries in 2 minutes or limits the next cycle to high heat, depending on when the fault happened. If the switch closes during low heat instead, the control flashes 31 and moves up to high heat. Single-stage 58STA and 58STX furnaces use code 31 for a different fault.
How do I fix Carrier furnace code 31?
From ground level, check the outdoor intake and exhaust ends and clear loose snow or leaves by hand if it's safe. Vent slope, drain, pressure, relay and gas valve wiring checks are technician work.
How much does it cost to fix Carrier furnace code 31?
Cost depends on what the technician finds: a vent or drain problem, a pressure switch or inducer, or the control relay and wiring.
Applies to
58MVP (Series 170/180) · 58MVB · 58UVB
Different Carrier generations use different code maps. If your series isn't listed, don't assume this meaning — check your blower-door label.
Verified against Carrier 58MVP/58MVB/58UVB Troubleshooting Guide (58-06T), p.7 — “HIGH-HEAT PRESSURE SWITCH OR RELAY DID NOT CLOSE OR REOPENED – Indicates the high-heat pressure switch input failed to close on a call for high-heat, or opened during high-heat. Control relay may be defective or gas valve is mis-wired. Refer to status code #32.”
Verified against Carrier 58MVP/58MVB/58UVB Troubleshooting Guide (58-06T), p.19-21 — “A miswired gas valve can cause this problem so make sure the BLUE wire goes to the gas valve M terminal and the GREEN/YELLOW wire goes to the gas valve C terminal.”
Verified against Carrier 58MVB Service and Maintenance Instructions (58MVB-2SM), p.18 — “Control relay may be defective. Gas valve is miswired. See status code 32.”
Last verified 2026-10-19 · page updated 2026-10-20 · how we verify
Related Carrier furnace codes
These codes use the same status led — two-stage variable-speed (58mvp / 58mvb / 58uvb) system.