DIY Error Codes

Rinnai Tankless water heater Code SS

SS (shown as 55 on some displays) is a time-based reminder that the heater is due for service, mainly a heat exchanger flush.

It is a reminder, not a failure. Schedule a heat exchanger flush, then reset SS.

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Full answer & models

Rinnai code SS means: Service Soon (time-based service reminder). It is a reminder, not a failure. Schedule a heat exchanger flush, then reset SS.

Applies to: SENSEI™ SeriesNon-SENSEI™ Series
Also searched as: Rinnai SS code, Rinnai error code 55, Rinnai code 55, Rinnai service soon

If you smell gas, leave the building and call your gas supplier from a neighbor's phone. Do not touch switches or use any phone inside.
Why
If you smell gas: do not try to light any appliance, do not touch any electrical switch, and do not use any phone in your building. Leave and call your gas supplier from a neighbor's phone; if you cannot reach them, call the fire department. Rinnai states that only trained and qualified professionals may follow its diagnostic-code service instructions, and that power, gas and water must be turned off before servicing. Never operate the heater with any vent pipe disconnected. Do not adjust the internal gas valve. Burn hazard (Rinnai): hot exhaust and vent may cause serious burns; keep small children and animals away, and hot water outlet pipes can be hot to touch.

What SS means

SS (shown as 55 on some displays) is a time-based reminder that the heater is due for service, mainly a heat exchanger flush.

More detail
Rinnai's diagnostic-code guide (page 58) titles code SS "Service Soon (time-based service reminder)". Rinnai's guide is written for trained, qualified professionals, so this page lists only the owner-level checks and tells you when to stop.

5-minute checks

Fix it step by step

Step 1 of 2

  1. Schedule a heat exchanger flush

    • 1-2 hr
    • None
    • Caution

    Rinnai says the heat exchanger should be flushed to prevent damage.

    More detail

    Schedule a heat exchanger flush.

    Rinnai's guide: SS indicates it is time for service. The heat exchanger should be flushed to prevent damage (see section 5.3, Flushing the Heat Exchanger, in your owner's manual). Hard water must be treated to prevent scale build-up.

    Did the code clear?

  2. Reset the SS reminder

    • 1 min
    • None
    • DIY

    Press On/Off on the temperature controller five times in five seconds.

    More detail

    Reset the SS reminder.

    Rinnai's guide: to reset the SS code, push the On/Off button on the temperature controller five times in five seconds. The reminder interval is Parameter 03.

    Still showing SS?Need a pro → call a pro

Code cleared. Nice work.

Watch the display for a day to make sure it stays clear.

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Fixed after any step? Watch the display for a day to make sure it stays clear. Still SS after step 2? call a pro.

Call a pro if…

  • You are not comfortable flushing the heater yourself.
  • Other codes appear along with SS.

FAQ

Is Rinnai 55 the same as SS?

Rinnai's guide lists the code as SS (55).

How do I reset SS?

Push On/Off on the temperature controller five times in five seconds.

Source: Rinnai, Troubleshooting Tankless Water Heater Diagnostic Codes (100000652), page 58. Written by the DIY Error Codes team. Updated 2026-10-16. DIY Error Codes is independent and not affiliated with or endorsed by Rinnai.