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Rinnai code 55: Service reminder

Continuous flow hot water system (Australia), tankless water heater (United States)

A time-based service reminder set at installation. The service period has passed; it is not a fault.

This needs a licensed gas technician. There are a few safe checks you can do first, marked below. Anything inside the unit is a job for a professional.

Only some models show this code. Check the list below.

What causes it

Australian gas continuous flow models

  1. The service interval your installer set has elapsed.

    Reset the Rinnai service reminderYou can do this

    1. The reminder means the service interval set at installation has passed. Contact Rinnai or your service provider to book the service, which includes flushing the heat exchanger. Hard water should be treated.
    2. To clear the reminder, press the On/Off button on the controller five times in quick succession.

Infinity Enviro 32 and Heavy Duty 32C

  1. The service interval set at installation has passed. Rinnai recommends commercial models are serviced every year.

    Same check as above: Reset the Rinnai service reminder

US tankless models

  1. The service interval set at installation has passed.

    Same check as above: Reset the Rinnai service reminder

    Have the heat exchanger flushed and descaled

How to read this code on your unit

Booking a licensed gas technician

Have the heat exchanger flushed and descaledplumber

  1. Scale from hard water builds up inside the heat exchanger and restricts flow and heat transfer.
  2. Book a licensed plumber or the manufacturer's service agent to flush and descale the heat exchanger using the manufacturer's flushing procedure.
  3. Ask about water treatment if you have hard water, so the scale does not come back.

Models that show this code

39 models in 8 ranges
RangeModels
Heavy Duty (commercial)REU-AM3237WC (HD32e), REU-VCM2837FFC (HD28i), REU-VCM2837WC (HD28e), REU-NB3237WC-AK (Heavy Duty 32C), REU-NB3237FFC-AK, REU-NB3237WC-50-AK, REU-NB3237FFC-50-AK
InfinityREU-AM3237W (Infinity 32), REU-AM2626WDL (Infinity 26 Touch), REU-AM2626WD (Infinity 26), REU-AM2024WD (Infinity 20), REU-AM1620WD (Infinity 16), REU-AM1220WD (Infinity 12), REU-A2626WB (B26), REU-A2024WB (B20), REU-A1620WB (B16)
Infinity BREU-BM2626W (Infinity B26), REU-BM2024W (Infinity B20), REU-BM1620W (Infinity B16), REU-BM1220W (Infinity B12)
Infinity EnviroREU-E2626W (Infinity Enviro 26), REU-E1620W (Infinity Enviro 16)
Infinity internalREU-VCM2837FF (Infinity 28i)
SENSEI commercialCU199i (REU-N3237FFC-US), CU160i (REU-N2530FFC-US), CU199e (REU-N3237WC-US), CU160e (REU-N2530WC-US)
SENSEI residentialRU199i (REU-N3237FF-US), RU180i (REU-N2934FF-US), RU160i (REU-N2530FF-US), RU130i (REU-N2024FF-US), RU199e (REU-N3237W-US), RU180e (REU-N2934W-US), RU160e (REU-N2530W-US), RU130e (REU-N2024W-US)
SENSEI residential with pumpRUR199i (REU-NP3237FF-US), RUR160i (REU-NP2530FF-US), RUR199e (REU-NP3237W-US), RUR160e (REU-NP2530W-US)

Where this comes from

Checked against the manufacturer's manual on 9 October 2026.

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Other Rinnai tankless water heater codes

Code Meaning What you can do
36 Lower tank thermistor fault Call a pro
38 Exhaust temperature thermistor fault Call a pro
41 Frost protection (ambient) sensor fault Call a pro
51 Inlet water thermistor fault Call a pro
52 Gas modulating valve fault Call a pro
54 High exhaust gas temperature Safe checks first, then a pro
57 Burner overheat switch open Call a pro
58 Secondary heat exchanger overheat Call a pro
61 Combustion fan failure Call a pro
63 Recirculation low flow Call a pro
65 Water flow control failure Safe checks first, then a pro
92 Neutraliser end of life Call a pro

See all maintenance reminder codes on tankless water heaters across brands.