What causes Rinnai Tankless Water Heater 11?

Gas turned off at the water heater, the gas meter or the propane cylinder. This is on Rinnai's own code 11 remedy list. An empty propane tank on LP systems. Air still in the gas lines, especially after a new installation. Rinnai's manuals say to bleed or purge all air from the gas lines. Wrong gas type for the heater, or inlet gas pressure that drops below the minimum on the rating plate when all the gas water heaters at the location fire on high. Rinnai points to an undersized gas line, meter, regulator or tank, or dirt in the gas system. The gas type DIP switch or programming parameters set wrong, or the high altitude setting not matched to the location. An igniter that doesn't spark, a damaged igniter wiring harness, or a spark electrode out of position (Rinnai specifies a 3.5 mm gap). Carbon or a white buildup on the flame rod, a loose flame rod, or a flame rod wire plugged into the wrong rod on heaters with more than one. Gas solenoid valves with an open or short circuit, burners not seated properly, or condensation or debris on the burner surface. Venting problems: a blocked flue outlet, loose joints, the wrong vent material, too long a vent run, or vent terminal clearances not met, which Rinnai says can recirculate exhaust and build carbon on the flame rod. A bad ground wire on the PC board, or a failed PC board.

How do I fix Rinnai Tankless Water Heater 11?

Check that the gas valve on the line going into the water heater is open, and that your other gas appliances work. If none do, call your gas utility. On propane, check the tank gauge and refill or swap the tank if it's low or empty. Go outside and look at the vent termination. Clear away snow, leaves, a nest or anything else blocking the flue outlet or air intake, without taking the vent apart. Close the hot water tap, then open it again to make the heater go through another ignition cycle. Rinnai's manual says the code stops flashing once the problem is corrected and the heater supplies hot water. If the heater was just installed or the gas was recently shut off, ask the installer to purge air from the gas line and confirm the gas type and DIP switch settings. If 11 keeps returning, stop retrying and call a licensed professional. Rinnai's manual marks the code 11 remedies as licensed professional only and says to call one for anything involving gas or electricity. If you smell gas at any point, leave the house and call your gas company from outside. Don't flip switches or try to relight anything.

When should I call a pro for Rinnai Tankless Water Heater 11?

Code 11 returns after the gas supply, propane level and vents check out. Measuring inlet gas pressure with every gas water heater at the location firing on high. Rinnai's manual says the rating plate minimum must be held, and on a properly sized black iron system the drop should be no more than 0.3 inches WC on natural gas or 0.5 inches on propane. Checking for spark, igniter wiring and PC board voltage to the igniter, and resetting the electrode gap to 3.5 mm. Removing and cleaning the igniter and flame rod, which needs a new gasket if the seal is broken, and checking the gas solenoid valves, burners and orifices. Checking that a two-stage propane regulator is at least six feet from the heater's gas inlet and doesn't let pressure bleed through above the heater's maximum when it shuts off. The heater is under warranty, or it's part of a multi-unit system (MSA or MSB), which Rinnai says should be isolated while troubleshooting.

Code: 11🚿 Rinnai Tankless Water Heater

Rinnai Tankless Error Code 11: No Ignition, Heater Won't Light (Meaning, Causes, Fixes)

Q: What does Rinnai Tankless Water Heater 11 mean?

Code 11 on a Rinnai tankless water heater means no ignition: the heater tried to light the burner and never detected a flame, so you get no hot water. Rinnai's own manual starts with the simple checks: make sure the gas is on at the water heater, the gas meter or the propane tank, that a propane tank actually has gas in it, and that nothing is blocking the flue outlet. If those are fine and 11 keeps coming back, Rinnai says the rest (gas pressure, line sizing, igniter, flame rod, gas valve) is for a licensed professional. Rinnai's Installation and Operation Manual lists code 11 as No Ignition (heater not turning on). Rinnai's Troubleshooting Tankless Water Heater Diagnostic Codes manual covers code 11 for its SENSEI and non-SENSEI models. In that manual, the technician watches the view window during the ignition cycle: if no flame ever appears, the problem is on the gas or spark side; if a flame does appear but the heater still shows 11, the issue is in the flame rectification (flame sensing) circuit, such as carbon or a white buildup on the flame rod, a bad flame rod connection, a loose or damaged flame rod, the PC board, the gas valve or low inlet gas pressure. Rinnai also notes that a loose, or floating, flame rod will cause a code 11. Code 11 is a close cousin of code 12 (flame failure, where the flame lights and then goes out), and Rinnai's manual says a loose flame rod or electrode can cause either one.

Reviewed 2026-10-22 · Based on 4 manufacturer & service sources

What the code means

Rinnai's Installation and Operation Manual lists code 11 as No Ignition (heater not turning on). Rinnai's Troubleshooting Tankless Water Heater Diagnostic Codes manual covers code 11 for its SENSEI and non-SENSEI models. In that manual, the technician watches the view window during the ignition cycle: if no flame ever appears, the problem is on the gas or spark side; if a flame does appear but the heater still shows 11, the issue is in the flame rectification (flame sensing) circuit, such as carbon or a white buildup on the flame rod, a bad flame rod connection, a loose or damaged flame rod, the PC board, the gas valve or low inlet gas pressure. Rinnai also notes that a loose, or floating, flame rod will cause a code 11. Code 11 is a close cousin of code 12 (flame failure, where the flame lights and then goes out), and Rinnai's manual says a loose flame rod or electrode can cause either one.

Likely causes

Gas turned off at the water heater, the gas meter or the propane cylinder. This is on Rinnai's own code 11 remedy list.
An empty propane tank on LP systems
Air still in the gas lines, especially after a new installation. Rinnai's manuals say to bleed or purge all air from the gas lines.
Wrong gas type for the heater, or inlet gas pressure that drops below the minimum on the rating plate when all the gas water heaters at the location fire on high. Rinnai points to an undersized gas line, meter, regulator or tank, or dirt in the gas system.
The gas type DIP switch or programming parameters set wrong, or the high altitude setting not matched to the location
An igniter that doesn't spark, a damaged igniter wiring harness, or a spark electrode out of position (Rinnai specifies a 3.5 mm gap)
Carbon or a white buildup on the flame rod, a loose flame rod, or a flame rod wire plugged into the wrong rod on heaters with more than one
Gas solenoid valves with an open or short circuit, burners not seated properly, or condensation or debris on the burner surface
Venting problems: a blocked flue outlet, loose joints, the wrong vent material, too long a vent run, or vent terminal clearances not met, which Rinnai says can recirculate exhaust and build carbon on the flame rod
A bad ground wire on the PC board, or a failed PC board

Safe DIY checks

⚠ Before you start

Unplug the appliance (or switch off its breaker) and shut off the water supply valves before removing panels or disconnecting hoses. Keep towels handy for residual water.

Check that the gas valve on the line going into the water heater is open, and that your other gas appliances work. If none do, call your gas utility.
On propane, check the tank gauge and refill or swap the tank if it's low or empty.
Go outside and look at the vent termination. Clear away snow, leaves, a nest or anything else blocking the flue outlet or air intake, without taking the vent apart.
Close the hot water tap, then open it again to make the heater go through another ignition cycle. Rinnai's manual says the code stops flashing once the problem is corrected and the heater supplies hot water.
If the heater was just installed or the gas was recently shut off, ask the installer to purge air from the gas line and confirm the gas type and DIP switch settings.
If 11 keeps returning, stop retrying and call a licensed professional. Rinnai's manual marks the code 11 remedies as licensed professional only and says to call one for anything involving gas or electricity.
If you smell gas at any point, leave the house and call your gas company from outside. Don't flip switches or try to relight anything.

🛠 When to call a pro

Code 11 returns after the gas supply, propane level and vents check out.
Measuring inlet gas pressure with every gas water heater at the location firing on high. Rinnai's manual says the rating plate minimum must be held, and on a properly sized black iron system the drop should be no more than 0.3 inches WC on natural gas or 0.5 inches on propane.
Checking for spark, igniter wiring and PC board voltage to the igniter, and resetting the electrode gap to 3.5 mm.
Removing and cleaning the igniter and flame rod, which needs a new gasket if the seal is broken, and checking the gas solenoid valves, burners and orifices.
Checking that a two-stage propane regulator is at least six feet from the heater's gas inlet and doesn't let pressure bleed through above the heater's maximum when it shuts off.
The heater is under warranty, or it's part of a multi-unit system (MSA or MSB), which Rinnai says should be isolated while troubleshooting.

Parts that commonly fix it

Always match the part number to your exact model.

⚙

Combustible gas leak detector

Handy for peace of mind around a gas water heater. Any real gas smell means leave and call the gas company, not a DIY check.

[affiliate link slot: AFFILIATE_SLOT_GAS_LEAK_DETECTOR]

⚙

Propane tank gauge

For LP installations, so an empty tank doesn't show up as a code 11 again.

[affiliate link slot: AFFILIATE_SLOT_PROPANE_GAUGE]

⚙

Rinnai igniter or flame rod and gasket (exact part for your model)

Technician part only. Rinnai marks code 11 remedies as licensed professional only.

[affiliate link slot: AFFILIATE_SLOT_TANKLESS_IGNITER]

Sources

Last reviewed 2026-10-22. Always confirm against the manual for your exact model number.

Rinnai Tankless Error Code 11: No Ignition, Heater Won't Light (Meaning, Causes, Fixes)

What the code means

Likely causes

Safe DIY checks

🛠 When to call a pro

Parts that commonly fix it

Combustible gas leak detector

Propane tank gauge

Rinnai igniter or flame rod and gasket (exact part for your model)

Related codes

Sources