System Diagnosis
High secondary voltage above normal range.
Rheem Furnaces
Error Code 59
Troubleshooting guide for the Rheem Furnaces system fault 59.
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
- Transformer output too high, incorrect transformer tap, abnormal line voltage, wiring issue, or control voltage outside the expected range.
- Verify against the exact unit manual.
Verify Before Replacing Parts
- Confirm the exact Rheem model family and furnaces context before acting on a generic code description.
- Start with line voltage, low voltage, and board output checks in sequence so the fault is isolated cleanly.
- Inspect connectors, relay outputs, and any recently replaced electrical parts for mismatch or loose fit.
- 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
Missing voltage, inconsistent outputs, or a fault that changes when a connector is reseated.
What can fool you
Intermittent power quality and field wiring problems can mimic a failed board.
When to Escalate the Call
- You have unstable supply power, repeated fuse failures, or signs of board damage.
- The failure path involves multiple boards or field-modified wiring.
Still unsure about this fault?
ACLogics walks you through Rheem Furnaces diagnostics step-by-step — so you confirm the cause before swapping parts.
