HVACopedia

Noritz · Tankless water heater troubleshooting

Descaling (flushing) the heat exchanger - Noritz

What is going on

Periodic descale for hard water. Scale causes 14/16/20/65 codes, unstable temperature, overheated water and clogged filters. A descale takes about 1 hour.

Likely causes

  • Hard water above 12 gpg (200 mg/L)
  • No softener or scale inhibitor

Check in this order

  1. Equipment 5 gallon bucket, 1/6 hp submersible pump, 2 flexible hoses and a 50/50 mix of water and calcium/lime/rust remover (Noritz kit DSCL-KIT).
  2. Units since 2016 have a Flush Mode for descaling (NC380-SV has no flush connector). On EZ/NRCR Pro there is no flush connector: start Scale Flushing from the EZ Start Plus app or display with the power button off.
  3. Turn off power and gas, close the water valves, connect the hoses to the isolation valve ports and circulate the solution per the installation manual.
  4. Use the hour to check intake/exhaust terminations, the internal intake filter, clean the ignition/flame rods and clean the fan and burner.
  5. Flush with clean water, clean the inlet filter (and NRCR return filter), restore water, gas and power.
  6. If the service reminder (C1#) was on, it clears after a correct flush.
  7. Recommend a softener or Scale Shield; treated water prevents scale better than descaling.

Applies to: All Noritz residential tankless (EZ, NRCR, NCC199CDV, NRC/NRCP)

More tankless water heater guides

Related

Noritz error codes · Noritz tips · Calculators and reference tables

Take it to the job

All guides, error codes and tips work offline in the HVACopedia app.

Open the app

Source: Noritz EZ/NRCR/CDV Level 2 Maintenance & Troubleshooting (Premix R2 V2), Water quality and descale procedure, p.3-6; Noritz Residential Level 2 Maintenance & Troubleshooting (NRC/NRCP and older, R2 V1), Descaling/flushing, p.2-4; Noritz NRCR Pro training (NRCR92/NRCR111, Printable V3), Service reminder / descaling, p.31-33; Noritz EZ/NRCR Owner's Guide (Rev. 10-25), Water quality and maintenance, p.28. 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.