Rinnai code 11: no ignition, causes and fixes

When a Rinnai tankless water heater shows code 11, it has tried to ignite the burner several times and the flame sensor never confirmed a flame. The unit shuts the gas off as a safety measure.

Start with the gas supply. It is the most common cause and the easiest to check.

What to check first

1. Make sure other gas appliances in the house work, such as the stove or furnace.
2. Check that the gas shutoff valve on the line to the water heater is fully open. The handle should line up with the pipe.
3. On propane, check the tank level. Units often show code 11 when the tank is low or was just refilled.
4. Turn the water heater off at the controller, wait a minute, turn it back on and open a hot water tap.

Common causes of Rinnai code 11

Air in the gas line

After a new installation, a gas meter change or a propane tank that ran empty, air in the line can keep the burner from lighting. Running hot water a few times often clears it.

Low gas pressure or an undersized gas line

Tankless heaters need a lot of gas at once. If code 11 shows up mostly when other gas appliances are running, the line may be too small or the pressure too low. A plumber can measure it.

Dirty flame rod or faulty igniter

The flame rod senses the flame. Buildup on it can make the unit think the burner did not light. Cleaning or replacing it is a job for a qualified technician.

Wrong gas type or failing gas valve

A unit set up for natural gas will not run properly on propane and the reverse. A failing gas valve can also cause code 11 and needs a service technician.

When to call a technician

Call a licensed technician if code 11 returns after a reset and you have confirmed the gas supply is on. The fault is then inside the unit, and Rinnai recommends that internal gas components be serviced by a licensed professional.