Tankless: error code, no ignition at low flow, or temperature swings
Many tankless complaints are water-side: flow below the activation threshold, a clogged inlet screen, low-flow aerators, or scale in the heat exchanger. Gas supply, venting and combustion codes are blocked: diagnose and refer. Read the code first, then work the water side.
Cross-checked ~90 min moderateBrands: Rinnai, Navien, Noritz, Rheem, A.O. Smith, Bradford White
Before you start
- Gas codes (ignition, flame loss, combustion, venting): no gas-side procedure; refer to a licensed gas technician
- CO risk: if venting codes repeat, shut the unit down and make sure CO alarms work
- Turn power off at the unit before opening the cabinet; 120 V inside
- Close the gas valve to the unit before descaling
Diagnostic steps
Unlock all 6 steps with expected values
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