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21

Fault code 21 — Shunt resistance unbalance adjustment fault

Rheem · Air Handlers

What does 21 mean?

There is an issue with the balance adjustment of the shunt resistance, possibly indicating a control board problem.

Common Causes

  • Control board fault

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Check the connections related to the shunt resistance.

  2. 2

    If connections are fine, the main PCB (control board) likely needs replacement.

Browse all codes in this manual (51)
Verified technical data. Last updated: April 2026

Related Faults

1Fault code 1 — Inverter DC voltage overload fault10Fault code 10 — PFC fault (level)11Fault code 11 — PFC power detection of failure
Source: Rheem Air Handlers
Open Manual (Page 186)Search more codes in this manual