System Diagnosis
High line voltage fault.
Rheem AC and Heat Pump
Error Code 28
Troubleshooting guide for the Rheem AC and Heat Pump system fault 28.
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
- Supply voltage above allowable range, incorrect electrical service, transformer/tap issue, or utility voltage problem.
- Verify voltage at the disconnect and unit.
Verify Before Replacing Parts
- Confirm the exact Rheem model family and ac and heat pump 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.
Not sure which system this Rheem code is on?
ACLogics has guided diagnostics for 57 Rheem fault codes and asks the right questions to narrow it down.
