Rheem dominates the Kansas City water heater market. Most Brookside, Waldo, Lee's Summit, and Overland Park homes have a Rheem tank or a Rheem-family tankless unit. Knowing how to read the error codes turns a panicked "no hot water" moment into a clear diagnosis and a same-day fix path.
Some Rheem codes reset cleanly and never return. Others repeat until the underlying cause is fixed. The table below covers what each code means and whether to attempt a reset before calling for service.
| Code | Meaning | Common Cause / Fix |
|---|---|---|
| 10 | Air Supply Problem | Vent obstruction, blocked intake, fan failure. Check vent termination first, especially after snow. |
| 11 | No Ignition | Gas supply, igniter, or flame rod issue. Most common Rheem code. Often resolves with flame rod cleaning. |
| 12 | Flame Failure | Flame detected then lost. Gas pressure drop under load or condensate drain blockage on condensing units. |
| 14 | Overheat | Heat exchanger overheating. Almost always scale buildup from KC hard water. Descaling required. |
| 16 | Temperature Exceeded | Outlet temperature beyond setpoint. Mixing valve or thermistor issue. Check thermistor resistance. |
| 21 | Solenoid Valve Issue | Gas solenoid valve fault. Usually requires valve assembly replacement. |
| 29 | Condensate Drain Blockage | Condensate cannot drain on condensing units. Clear the drain line and trap. |
| 31 | Combustion Fan Issue | Fan motor or wiring fault. Sometimes resolves with cleaning. Often replacement. |
| 32 | Thermistor Issue | Inlet or outlet thermistor reading out of range. Replace the affected sensor. |
| 34 | Combustion Fan Speed | Fan running outside expected RPM. Wiring, motor, or control board fault. |
| 35 | Thermistor (Different Circuit) | Secondary thermistor failure. Same diagnosis as 32 on a different sensor. |
| 52 | Modulating Solenoid | Gas modulation control fault. Affects flame size adjustment. Valve replacement typical. |
| 61 | Combustion Fan Motor | Motor failure. Replacement required. |
| 65 | Water Flow Sensor | Flow turbine fault. Often scale-related in KC. Sometimes cleaning, sometimes replacement. |
| 72 | Flame Rod Contamination | Flame rod dirty or oxidized. Cleaning usually resolves. Same root cause as many code 11 events. |
| 79 | Exhaust Blockage | Vent termination blocked. Ice, debris, animal nests in outdoor terminations. |
| 90 | Main Component Issue | Major control or component failure. Often replacement decision on older units. |
Newer Rheem tank units with electronic ignition use LED flash patterns rather than numeric displays. A single flash typically indicates normal operation. Repeated short flashes signal pilot or ignition issues. Long flash patterns indicate gas valve faults. The exact pattern key is on a label inside the access door of the unit.
For older Rheem tanks with standing pilots, no error codes exist — diagnosis is mechanical. The no hot water page covers tank-side diagnosis paths.
Tankless reset. Press and hold the power button on the controller for 5 seconds, release, and press again to power back on. The displayed error code clears. If the underlying cause is unresolved, the same code returns within minutes.
Gas tank reset. Turn the gas valve to OFF, wait 5 minutes for any gas to dissipate, then relight the pilot following the instructions on the unit label. Modern units have a piezo igniter button.
Electric tank reset. Turn off the dedicated breaker at the main panel. Press the red reset button on the high-limit switch behind the upper access panel. Restore power. If the high-limit trips again, do not keep resetting — there is a real fault.
Heat exchanger failure codes (repeated 14, 16, or codes pointing to specific exchanger sensors) on units 8+ years old often indicate the unit is approaching end of life. Heat exchanger replacement on a Rheem tankless sometimes costs nearly as much as a new unit, tilting the math toward replacement.
Main control board failures (code 90 or repeated unrelated codes) on older units also point toward replacement. A new control board on a 10-year-old unit installs into a chassis with everything else also aging.
Single-occurrence codes related to ignition (10, 11, 72) or sensors (32, 35, 65) almost always indicate routine repair regardless of age.
Code 14 (overheat), code 12 (flame loss under load), and code 65 (flow sensor) all spike in frequency on units that have skipped annual descaling. Scale buildup reduces water flow through the heat exchanger, which causes the exchanger to heat too quickly and trip overheat protection. The same scale interferes with flow sensor readings.
Annual descaling prevents most of these. See the tankless water heater service page for descaling details and the maintenance guide for the full preventive schedule.
Read the Rheem error code during the call for instant diagnosis and same-day repair across the KC metro.
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