System Diagnosis
High-Heat Pressure Switch or Relay Did Not Close or Reopened. High-heat pressure switch input failed to close on a call for high heat, or opened during high heat.
Carrier | Furnaces
Error Code 31
Troubleshooting guide for the Carrier Furnaces system fault 31.
Disclaimer: This information is for general reference. Error codes can vary by model and production year. Always refer to your machine's specific manual and the information printed on the unit itself.
Potential Causes & Solutions
- Check inducer motor speed and operation.
- Inspect pressure switch tubing for blockage or leaks.
- Test high-heat pressure switch with manometer.
- Verify vent system is clear and properly sized.
Verify Before Replacing Parts
- Confirm the exact Carrier model family and furnaces context before acting on a generic code description.
- Walk the entire heating sequence in order instead of jumping straight to the reported code.
- Verify each safety device and prove where the sequence stops under live operation.
- After the correction, run the system long enough to confirm the code does not return under normal load.
Field Signals to Confirm
What usually confirms it
A repeatable stop in the heating sequence at the same safety or prove step.
What can fool you
Weak grounding, marginal flame signal, or venting issues can produce inconsistent code behavior.
When to Escalate the Call
- Safety devices keep opening after the obvious mechanical causes are corrected.
- Combustion, venting, or gas input needs a higher-confidence review.
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