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All brands · Tankless water heater troubleshooting

No hot water

What is going on

Water runs but never gets hot, and the unit may or may not show an error code.

Likely causes

  • Flow below the unit's minimum activation flow
  • Gas supply off or undersized gas line
  • Clogged inlet water filter
  • Plumbing crossover
  • Unit in error or lockout

Check in this order

  1. Check the remote or display for an error code and look it up under Error Codes
  2. Open a hot tap fully and confirm flow is above the minimum activation flow
  3. Clean the inlet water filter
  4. Confirm gas is on and check inlet gas pressure at full fire
  5. Check for a crossover shut the cold inlet and see if water still flows from hot taps
  6. Verify power to the unit

Applies to: Tankless water heaters

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Source: General HVAC service practice — verify per model. Written in our own words; check the manual for your exact model.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.