Code: 70🚿 Rinnai Tankless Water Heater

Rinnai Tankless Error Code 70: PC Board Fault (Meaning, Causes, Fixes)

Reviewed 2026-10-23 · Based on 2 manufacturer & service sources

What the code means

In Rinnai's installation and operation manual error table, code 70 is listed simply as "PC Board", with the remedy "Replace the PC Board". Rinnai's Troubleshooting Tankless Water Heater Diagnostic Codes guide (code 70 applies to both SENSEI and non-SENSEI series) gives a slightly longer checklist before replacing the board: confirm all water heater parameters were set properly, and check every wiring harness at its connection to the PC board for loose, broken or damaged connections. So code 70 means the control board itself is suspected, unlike code 71, which is a fault in the gas solenoid valve circuit the board drives.

Likely causes

Safe DIY checks

⚠ Before you start

Unplug the appliance (or switch off its breaker) and shut off the water supply valves before removing panels or disconnecting hoses. Keep towels handy for residual water.

  1. Note the code and when it appeared. If the unit has a temperature controller with diagnostic history, write down any other recent codes for the technician.
  2. Turn the water heater's power off, wait a minute, and turn it back on. If code 70 doesn't return, keep an eye on it.
  3. If anyone recently changed settings, installed the unit or replaced parts, tell your installer, since Rinnai's first check for code 70 is that all parameters were set properly.
  4. Don't open the unit or unplug harnesses yourself. Rinnai's code tables mark these repairs for a licensed professional, and the unit has gas, water and line-voltage connections inside.
  5. If code 70 comes back, call a Rinnai-authorized technician or Rinnai support, and have the model and serial number from the rating plate ready.

🛠 When to call a pro

  • Code 70 returns after a power reset.
  • Checking the parameter settings and the wiring harness connections at the PC board, as Rinnai's troubleshooting guide lists.
  • Replacing the PC board. On SENSEI series models, Rinnai says the data has to be transferred from the old board to the new one with the data-transfer cable that comes with the new board, or the parameters programmed by hand using the instructions included with it.
  • Any smell of gas or exhaust. Leave the area and call your gas company.
  • The unit is still under warranty. Have a Rinnai-authorized technician handle the board.

Parts that commonly fix it

Always match the part number to your exact model.

⚙

Rinnai PC board (exact part for your model)

Technician part only. Rinnai lists replacing the PC board as the fix for code 70; SENSEI models need a data transfer or manual parameter programming after the swap.

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⚙

Combustible gas leak detector

For peace of mind around a gas water heater. A real gas smell means leave and call the gas company, not a DIY check.

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Sources

  1. Rinnai Troubleshooting Tankless Water Heater Diagnostic Codes, Code 70 (page 49): applies to SENSEI and non-SENSEI series; check parameters, check harnesses at the PC board, replace PC board, SENSEI data transfer or manual programming
  2. Rinnai Installation and Operation Manual (V53De), error codes table: 70 PC Board, Replace the PC Board (licensed professional only)

Last reviewed 2026-10-23. Always confirm against the manual for your exact model number.