5 FLASH
Rheem · Rheem Professional Classic 50 Gal. 38,000 BTU Natural Gas Water Heater
The electronic temperature sensor inside the gas control valve is reading out of range or has failed. On modern Rheem gas water heaters with Honeywell/Resideo gas controls, the temperature sensor is integrated into the gas control valve assembly and CANNOT be replaced separately. The entire gas control valve must be replaced. Before replacing, verify all wiring and connections are intact. Use the correct replacement gas control valve part number for your specific water heater model — gas controls are NOT interchangeable between models due to different temperature calibrations and gas types.
Error 5 FLASH on the Rheem Rheem Professional Classic 50 Gal. 38,000 BTU Natural Gas Water Heater means: Temperature Sensor Failure. The top-ranked community fix is “Replace Entire Gas Control Valve Assembly” (hard difficulty, ~90 min, DIY cost: $0-$20). 2 community-ranked fixes available below.
Published February 2026 · 2 fixes · water heater
Content is based on manufacturer service documentation, community repair experience, and OEM technical bulletins. Always verify with your owner's manual.Learn about our editorial standards.
While many water heater repairs can be done safely at home, consider hiring a qualified technician if:
Average professional repair cost for this issue: $350-$500.
Normal Operation
Thermopile Voltage Low
Temperature Exceeded High Limit
Gas Control Valve Electronics Failure
Insufficient Thermopile Power
Not Enough Hot Water — Runs Out Quickly
No Hot Water — Pilot Light Out
Rumbling or Popping Noises During Heating
The Rheem Rheem Professional Classic 50 Gal. 38,000 BTU Natural Gas Water Heater has 8 other known error codes:
Error code 5 FLASH also appears on 2 other Rheem models:
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