Rinnai code 70: control board fault

The PC board is the heater's control center. Code 70 means it has detected a fault in its own operation or setup.

The meaning and service steps below come from Rinnai's own diagnostic code guide for its tankless water heaters.

Checks before a new board

1. Confirm the heater's settings (parameters) were set correctly during installation.
2. Check every wiring harness at the board for loose, broken or damaged connections.
3. Only then replace the board.

After a board replacement

On SENSEI and SENSEI RX/CX models, Rinnai has technicians move the settings from the old board to the new one using a data transfer cable included with the new board. If that is not possible, the settings are programmed by hand following Rinnai's instructions. Skipping this step can cause new problems.

How to reset it

1. Close all hot water taps.
2. Turn the water heater off at the temperature controller, wait about a minute, then turn it back on.
3. Open a hot tap and watch whether the code returns.

If the same code keeps coming back, the cause is still there. Repeated resets are not a repair.

Protecting the board

• Use a properly grounded outlet and consider an appliance-rated surge protector.
• Keep water from dripping onto the unit from pipes or the vent.

A control board is one of the pricier parts on a tankless heater, so check whether it is still under warranty before paying for one.

Before you call

Have the model and serial number from the rating label ready, along with the exact code and when it appears: at startup, during use, or only at high demand. Mention any recent work on the gas, water or electrical supply and when the heater was last descaled. This helps the technician bring the right parts and often saves a second visit.

See every code on our Rinnai error codes page.