On the covered Rinnai tankless water heater, 70 means a PC board fault. First, reset the water heater's power once. Then: Rinnai's only action is to replace the PC board, which is a technician repair. Rinnai's action is to replace the board.
Differential
Likely causes of “Rinnai tankless water heater code 70”, and how to tell them apart
- 1
A failed control (PC) board
What separates it The code returns on every reset
How to confirm Rinnai's action is to replace the board
- 2
A power surge or lightning
What separates it The fault followed a storm
How to confirm Technician diagnosis
- 3
Moisture on the board
What separates it A leak or condensation nearby
How to confirm Fix the leak and have the board checked
- 4
A bad connection to the board
What separates it Intermittent faults
How to confirm A technician checks the connectors
- 5
An unsuitable power supply
What separates it Voltage problems
How to confirm Check the supply
Before you touch a setting
Record this first — changing settings destroys the evidence
- Whether the code followed a storm or surge
- Whether there is water near the unit
- Whether it clears after a reset
- The model number
Try in this order
0 of 7 completedWhat to do first
ReversibleReset the water heater's power once.
Correct only the documented fault domain
ReversibleRinnai's only action is to replace the PC board, which is a technician repair.
Check for water nearby
ReversibleFix any leak.
Check the supply voltage
ReversibleVia an electrician.
Do not keep resetting
ReversibleThe board will not heal.
Note the model number
ReversibleFrom the rating plate.
Call a technician
ReversibleTo replace the board.
Model-specific
What is true of this model and not of its siblings
- The PC board
- The printed circuit board runs the heater: it reads the sensors, controls the fan and the gas valve and shows codes. Because every function depends on it, a board fault stops the unit rather than reducing performance.
- What damages boards
- Surges, moisture and heat are the usual causes. A heater installed where condensation or a leak can reach the board, or on a circuit without surge protection, is more at risk.
- Replacement
- Rinnai's only step is a new board, fitted by a licensed technician, who will also check why the old one failed.
- What the board controls
- The PC board is the heater's brain. It reads the flow, temperature and flame sensors, drives the fan, the gas valve and the igniter, and shows codes. A failed board often produces several unrelated codes or none that make sense.
- Before blaming the board
- A technician checks the supply voltage, the connectors and the signs of moisture or burning first, because a board fault is often a symptom of a leak, a surge or a loose connector. Replacing a board without finding the cause invites a repeat.
- Warranty and cost
- Boards are among the dearer parts. Check the warranty, the installation date and whether the heater was registered with the manufacturer.
- Questions to ask a technician
- Ask what caused the board to fail, whether the sensors and the fan were tested and whether the repair includes a warranty on the new board. A heater that has failed once on a board should be checked for moisture, surge protection and the quality of the supply.
- What owners can do while waiting
- Without hot water, plan around the repair time: ask the technician for the part's availability, since boards may need ordering. Turn the heater's power off at the isolator so that it is not repeatedly attempting to start, and keep the water supply on so the pipes are not drained unnecessarily.
Stop boundary
When this stops being a self-service repair
- !Rinnai's only action is to replace the PC board, a technician repair
- !Disconnect power before any inspection
- !Do not open the unit
Evidence ledger
Sources behind this answer
Exact questions
Common questions
What does 70 mean on a Rinnai tankless water heater?+
A PC board fault.
Can I replace it?+
Rinnai says a technician must.
Could a surge cause it?+
It can.
Is it covered?+
Check your warranty.