Rinnai Error Code 999: PC Board / software mismatch (Boiler)

Updated October 13, 2026 · by Aurora Star Tech Inc.

Rinnai error code 999 on a boiler means: PC Board / software mismatch. It is also called Rinnai diagnostic code 999.

High severityBoilerAlso Combi BoilerI-Series Plus 150K and smaller · I-Series Plus 175K and higher

Homeowner? What Rinnai code 999 means for you

Call a technician Your boiler is reporting: PC Board / software mismatch. The boiler has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.

Safe things you can check yourself

Check the thermostat: right mode (Heat or Cool), set a few degrees past room temperature, and fresh batteries if it uses them.
Make sure the unit has power: its on/off switch (often looks like a light switch near the unit) is ON and the breaker in the electrical panel is not tripped.
Look at the pressure gauge on the boiler. If it reads much lower than usual or near zero, or water is leaking, call a technician.
Outside, make sure the intake and exhaust pipes or vent cap are not blocked by snow, ice, leaves or a nest.
Check that the boiler gas valve is open (handle in line with the pipe).
Try one reset: turn the power off for 30 seconds, then back on. If the code comes back, stop resetting and call a technician.

Call (647) 657-2977 Book a service call

Licensed technicians serving Vaughan, Toronto and the GTA.

What does Rinnai error code 999 mean?

The PC Board and the internal logic do not match.

Applies to: I-Series Plus boilers — 150K BTU and smaller and 175K BTU and higher (Combi and Solo)

Common causes of Rinnai code 999

Harnesses connected to the wrong terminals
Wet or corroded board connections
Software version mismatch between PC Board and operation board

A technician checks these and 1 other possible causes on site before replacing any part.

Safety: Gas, electrical and refrigerant work must be done by a licensed technician. Turn off power and gas before servicing, never bypass a safety control, and always follow the manufacturer's manual for your exact model.

Rinnai models that use code 999

IP060S IP090S IP120S IP150S IP175S IP199S

Other Rinnai Boiler codes

Code	Meaning
700	PC Board fault
710	Gas solenoid circuit – valve position mismatch
720	Flame rod fault
763	0-10V external control input over-voltage
831	Indirect tank call running too long
890	Freeze condition detected
FFF	Maintenance performed marker
SS	Service Soon reminder

All Rinnai Boiler error codes →

Rinnai code 999: homeowner questions

What does Rinnai code 999 mean?

PC Board / software mismatch. The PC Board and the internal logic do not match.

Is it safe to keep using my boiler with code 999?

It depends on the cause. The boiler has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.

Can I reset Rinnai code 999 myself?

You can try one reset (power off for 30 seconds, then on). If Rinnai code 999 comes back, the cause is still there and a licensed technician should check it.

Who can fix Rinnai code 999 near me?

Aurora Star Tech Inc. repairs Rinnai boilers in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.

Homeowner help: Boiler Not Heating: What to Check

Troubleshooting guides

No heat or some zones cold All brands · Boiler

Source: Rinnai Troubleshooting I-Series Plus Boiler Diagnostic Codes (800000375), p.45. Written in our own words as a summary; always check the original manual.

General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.