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Rinnai · Tankless water heater

07 Circulation flow rate below 2.1 GPM

Medium severity RH180 hybrid

What the control is telling you

On the RH180 hybrid, the water circulating through the unit has dropped below 2.1 GPM.

Applies to: RH180 hybrid tank-tankless (non-SENSEI) only

Likely causes

  • No power to the unit
  • Water supply off, or supply pressure under 30 PSI
  • Pump not running, or pump wiring loose/damaged
  • Clogged inlet water filter
  • Scale build-up in the heat exchanger

Test and repair steps

  1. Make sure the unit has power.
  2. Make sure the water supply is on and pressure is at least 30 PSI.
  3. Check that the pump runs, and check its wiring harness for loose, damaged or broken connections.
  4. Drain the tank and clean the inlet water filter.
  5. Flush the heat exchanger to remove scale, following the flushing procedure in the Installation and Operation Manual.

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Source: Rinnai Troubleshooting TWH Diagnostic Codes (100000652), p.11. Summarized in our own words; check the original manual for your model.

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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.