8 FLASH
Rheem · Rheem Professional Classic 50 Gal. 38,000 BTU Natural Gas Water Heater
Similar to the 2-flash code but indicates a more critical level of power generation failure. The thermopile output voltage is too low to sustain gas valve operation. The pilot may light and stay on while you hold the gas control knob in the PILOT position, but it goes out within seconds of releasing the knob. This means the thermopile cannot generate enough voltage to hold the gas valve open. On some models, the pilot assembly, thermocouple, thermopile, and igniter are an integrated unit that must be replaced as a complete assembly. Replace the thermopile or complete pilot assembly. After replacement, verify the pilot flame fully engulfs the thermopile tip for maximum heat exposure.
Error 8 FLASH on the Rheem Rheem Professional Classic 50 Gal. 38,000 BTU Natural Gas Water Heater means: Insufficient Thermopile Power. The top-ranked community fix is “Replace the Thermopile or Complete Pilot Assembly” (medium difficulty, ~60 min, DIY cost: $80-$120). 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: $200-$350.
Normal Operation
Thermopile Voltage Low
Temperature Exceeded High Limit
Temperature Sensor Failure
Gas Control Valve Electronics Failure
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 8 FLASH also appears on 2 other Rheem models:
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