Rheem Tankless Error Code 11

What happens when a tankless heater won't light

A gas tankless heater only fires when hot water flows. The unit senses the flow, starts the combustion fan, sparks the igniter and opens the gas valve, and flame rods confirm the burner is lit. Rheem's burner bulletin shows the igniter and flame rods unplugging by a connector on the burner assembly. If that confirmation never comes, the controller shuts off the gas and posts a code.

The code tells you the result, not the cause. The cause is somewhere in gas, air or the ignition parts.

Common causes, in the order a tech checks them

1. Gas supply. A closed valve, an empty propane tank, or air in the line after gas work.
2. Gas pressure. A line or regulator too small for the heater can starve it the moment it fires, especially when the furnace or range runs too.
3. Venting and combustion air. A blocked vent cap or intake chokes the burner.
4. Dirty flame rod or igniter. Rheem's burner cleaning bulletin tells technicians to remove the carbon buildup on the flame rod with steel wool, emery cloth or fine sandpaper. A coated flame rod can't confirm a flame that's actually there.
5. Control or valve failure. Rarer, and always a service call.

Rinnai's checklist for its own code 11, which it names "No Ignition," follows the same order, starting with the gas supply and ending at the igniter and gas valves. Different brand, same physics.

Safe checks you can do

• Check the gas valve on the pipe feeding the heater. On a typical quarter-turn valve, the handle runs in line with the pipe when it's open.
• Check another gas appliance. If the stove won't light either, call the utility. The heater isn't the problem.
• On propane, check the tank. If it ran empty, the lines may need purging after the refill before the heater lights reliably.
• Check the vent cap and air intake outside for snow, ice, leaves, nests or overgrown shrubs.
• Check power to the unit. A tripped breaker or unplugged cord can show up as a fault too.
• Reset once. Turn the heater off at its controller, wait a minute, turn it back on and open a hot tap fully.

If the code comes back right away, stop resetting it. A real ignition fault won't fix itself, and sending gas over and over into a heater that won't light is a bad habit.

When to call a technician

Call when the gas is on, the vent is clear and the code keeps returning. Measuring gas pressure at high fire, cleaning the flame rod, checking the igniter and testing the gas valve all mean taking the front off the unit. Rheem tells servicers to contact its technical service line at 800-432-8373 with the unit's serial number ready, so expect your tech to have that number on the rating plate handy.

For budgeting, HomeGuide puts tankless water heater repairs at $300 to $1,300 on average. If the heater hasn't been descaled recently, a flush on the same visit is worth asking about. See how to flush a tankless water heater.

Which Rheem heaters this applies to

Rheem's tankless gas burner bulletin covers a long list of models across its RTG, RTGH, ECO and related families with a "-3" suffix. Error code tables can differ between generations and between condensing and non-condensing units, so match the code to your model's manual before buying parts.

If you're weighing a big repair on an older unit, compare it with tankless water heater cost, and see our tankless water heater repair guide for the wider picture.