What causes Rheem Gas Furnace 11?

A dirty, corroded or loose flame sensor rod, so the control can't see the flame even when the burners light (Rheem lists this first). The gas valve switched off, or the gas supply to the furnace shut off. An igniter that isn't working, isn't connected properly, or is out of position. Flame not spreading from the first burner to the last, often with low manifold gas pressure. A poor furnace ground, or line and neutral wired backwards (a separate Rheem code, 26, flags reversed polarity). A failed furnace control board.

How do I fix Rheem Gas Furnace 11?

Read the display carefully. 11 by itself means the furnace is still retrying; 10 and 11 alternating means it has failed four times and is in the one-hour lockout. Make sure the gas is on: the manual shutoff on the gas line to the furnace should be in line with the pipe, the switch on the furnace gas valve should be ON, and other gas appliances should be working. If you smell gas, don't touch anything and leave (see below). Check that the furnace door is on and the thermostat is calling for heat, then reset by turning off power at the furnace switch or breaker (or setting the thermostat to off) for 5 to 10 seconds, which is how Rheem says to clear the ignition lockout. Watch through the window whether the igniter glows or sparks and whether the burners light. If the burners light for a few seconds and then shut off, the flame sensor is the likely culprit. With power and gas off, a handy homeowner can remove the sensor rod (usually one screw), gently clean it with fine steel wool or a fine abrasive pad, and reinstall it with its wire firmly attached. If you're not comfortable working near the burners, leave this to a technician. If 11 keeps coming back after a reset, stop resetting and call a technician. Repeated failed ignitions mean gas, ignition or flame-sensing problems that need testing.

When should I call a pro for Rheem Gas Furnace 11?

Checking manifold gas pressure during ignition with a manometer. Rheem's 802V manual gives approximately 3.5 in. w.c. for natural gas and 10 in. w.c. for LP, and says to watch whether the flame carries from the first burner to the last; if pressure is good and later burners don't light, a burner may need replacing. Replacing or repositioning the igniter, or repairing the wiring between the igniter and the furnace control. Cleaning or replacing the flame sensor, checking its wire to the control, and confirming the furnace ground is properly connected. Replacing the furnace control if gas, ignition and flame sensing all check out. You smell gas or a carbon monoxide alarm sounds. Leave the house and call your gas utility from outside.

Code: 11🔥 Rheem Gas Furnace

Rheem Furnace Code 11: Failed Ignition (Meaning, Fixes)

Q: What does Rheem Gas Furnace 11 mean?

Code 11 on a Rheem (or Ruud) gas furnace with a two-digit display means Failed Ignition: the furnace tried to light the burners and the control never sensed a flame. It retries on its own, but after four failed tries in a row it goes into a one-hour lockout and the display alternates 10 and 11. Rheem's most common causes are a dirty or loose flame sensor, a gas valve that's turned off, an igniter problem, flame not carrying across all the burners, or a failed control board. Rheem's fault code label for its communicating furnaces lists 11 as Failed Ignition, in the flame-sense group alongside 10 (one-hour lockout), 12 (low flame sense), 13 (flame lost) and 14 (unexpected flame). Rheem's 802V installation instructions say the code appears after the first failed ignition attempt. The inducer then runs a 20-second post-purge and the furnace tries again, up to four times. Up to three failures isn't treated as critical; after the fourth the control enters a one-hour lockout, shows 10 and 11 alternately, and won't run gas heat, though cooling and other modes still work. On a communicating thermostat the homeowner usually only sees it once it happens at least three times in one heat call. Code 11 is about the burner not lighting or the flame not being proven; if the flame lights and then drops out, that's code 13 instead, and a weak but present flame signal is code 12.

Reviewed 2026-10-23 · Based on 3 manufacturer & service sources

What the code means

Rheem's fault code label for its communicating furnaces lists 11 as Failed Ignition, in the flame-sense group alongside 10 (one-hour lockout), 12 (low flame sense), 13 (flame lost) and 14 (unexpected flame). Rheem's 802V installation instructions say the code appears after the first failed ignition attempt. The inducer then runs a 20-second post-purge and the furnace tries again, up to four times. Up to three failures isn't treated as critical; after the fourth the control enters a one-hour lockout, shows 10 and 11 alternately, and won't run gas heat, though cooling and other modes still work. On a communicating thermostat the homeowner usually only sees it once it happens at least three times in one heat call. Code 11 is about the burner not lighting or the flame not being proven; if the flame lights and then drops out, that's code 13 instead, and a weak but present flame signal is code 12.

Likely causes

A dirty, corroded or loose flame sensor rod, so the control can't see the flame even when the burners light (Rheem lists this first)
The gas valve switched off, or the gas supply to the furnace shut off
An igniter that isn't working, isn't connected properly, or is out of position
Flame not spreading from the first burner to the last, often with low manifold gas pressure
A poor furnace ground, or line and neutral wired backwards (a separate Rheem code, 26, flags reversed polarity)
A failed furnace control board

Safe DIY checks

⚠ Before you start

Turn off power at the furnace/HVAC service switch and the breaker before opening panels. Shut the gas valve before any work near the burners, and never disconnect or alter the gas line. If you smell gas, leave the house and call your gas utility.

Read the display carefully. 11 by itself means the furnace is still retrying; 10 and 11 alternating means it has failed four times and is in the one-hour lockout.
Make sure the gas is on: the manual shutoff on the gas line to the furnace should be in line with the pipe, the switch on the furnace gas valve should be ON, and other gas appliances should be working. If you smell gas, don't touch anything and leave (see below).
Check that the furnace door is on and the thermostat is calling for heat, then reset by turning off power at the furnace switch or breaker (or setting the thermostat to off) for 5 to 10 seconds, which is how Rheem says to clear the ignition lockout. Watch through the window whether the igniter glows or sparks and whether the burners light.
If the burners light for a few seconds and then shut off, the flame sensor is the likely culprit. With power and gas off, a handy homeowner can remove the sensor rod (usually one screw), gently clean it with fine steel wool or a fine abrasive pad, and reinstall it with its wire firmly attached. If you're not comfortable working near the burners, leave this to a technician.
If 11 keeps coming back after a reset, stop resetting and call a technician. Repeated failed ignitions mean gas, ignition or flame-sensing problems that need testing.

🛠 When to call a pro

Checking manifold gas pressure during ignition with a manometer. Rheem's 802V manual gives approximately 3.5 in. w.c. for natural gas and 10 in. w.c. for LP, and says to watch whether the flame carries from the first burner to the last; if pressure is good and later burners don't light, a burner may need replacing.
Replacing or repositioning the igniter, or repairing the wiring between the igniter and the furnace control.
Cleaning or replacing the flame sensor, checking its wire to the control, and confirming the furnace ground is properly connected.
Replacing the furnace control if gas, ignition and flame sensing all check out.
You smell gas or a carbon monoxide alarm sounds. Leave the house and call your gas utility from outside.

Parts that commonly fix it

Always match the part number to your exact model.

⚙

Furnace control board (exact OEM match)

Last suspect, only after gas pressure, igniter and flame sensor check out, per Rheem's solution list.

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⚙

Digital multimeter

For checking the ground, line polarity and igniter and wiring continuity.

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⚙

Gas leak detector

Handy for checking the gas line and valve connections after any gas-side work.

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Sources

Last reviewed 2026-10-23. Always confirm against the manual for your exact model number.

Rheem Furnace Code 11: Failed Ignition (Meaning, Fixes)

What the code means

Likely causes

Safe DIY checks

🛠 When to call a pro

Parts that commonly fix it

Furnace control board (exact OEM match)

Digital multimeter

Gas leak detector

Related codes

Sources