Rinnai continuous flow hot water system code 18: Gas valve adjustment limit

Continuous flow hot water system, Australia

The heater reported that its gas valve adjustment has reached its limit.

This needs a licensed gasfitter. There is nothing safe to check yourself. Leave the covers on and book a professional.

This involves the gas supply or burner. Only a licensed technician should open the unit or work on gas parts.

What causes it

A gas valve adjustment fault. Rinnai lists this as needing a service call.

Book a licensed gasfitter

Turn the unit off and leave the covers on. Gas components must only be serviced by a licensed technician.
Note the code, how often it appears, and the model and serial numbers from the rating label.
Book a licensed gasfitter and give them those details.

6 models in 2 ranges

Range	Models
Heavy Duty (commercial)	REU-NB3237WC-AK (Heavy Duty 32C), REU-NB3237FFC-AK, REU-NB3237WC-50-AK, REU-NB3237FFC-50-AK
Infinity Enviro	REU-NB3237W-AK (Infinity Enviro 32), REU-NB3237W-50-AK

Checked against the manufacturer's manual on 9 October 2026.

Code	Meaning	What you can do
13	Combustion fault	Safe checks first, then a pro
14	Overheat safety device tripped	Call a pro
15	Venturi control failure	Safe checks first, then a pro
16	Over-temperature shutdown	Safe checks first, then a pro
17	Venturi blockage	Safe checks first, then a pro
19	Electrical earth fault	Call a pro
21	Data transfer or dip switch error	Call a pro
22	Gas valve adjustment fault	Call a pro
25	Sensor fault or condensate blockage (depends on model)	Depends on your model
32	Outgoing water temperature sensor fault	Call a pro
52	Gas modulating valve fault	Call a pro
71	Gas solenoid valve failure	Call a pro