Lennox Furnace Error Codes: What Each Code Means

By Ray Bennett · Updated 2 October 2026 · 6 min read · Checked against the maker’s manual

Lennox Furnace Error Codes: What Each Code Means

Short answer

Older Lennox furnaces flash a light 1 to 9 times, and newer ones show codes like E223 or E250 on a small display. E223 and E227 are the pressure switch and the venting, E250 and E311 are airflow, E240 and E273 are a dirty flame sensor, and E241 means flame where there should be none, which is the one to shut the gas off for.

Lennox furnaces report faults in one of two ways. Many single stage models flash a light on the control board a set number of times. Newer furnaces with a small display show a four character code such as E223 or E250.

Everything on this page comes from Lennox’s own installation instructions: document 507323-01 for the ML180UH, which uses flash codes, and 508245-01 for the SL280UHV, which uses E codes. Your furnace’s own label has the final word.

Before you start

What to carry: a torch and a pen. Ten minutes.

Gas or electric? These are gas furnace codes. Lennox heat pumps and air handlers have their own alerts, often shown on the thermostat.

Read it before opening anything. Look through the window in the lower door. The door has a safety switch, and on the newer controls Lennox even has a code for it being open: E370.

Three codes that mean shut the gas off, not reset. 1 flash on the older control, or E241 on the newer one. Lennox describes these as flame present with the gas valve off, or flame sensed out of sequence. Its instruction for E241 is to shut off the gas and check the valve for a leak.

E275. The same fault after it has locked out. Same response.

5 flashes, or E200: the rollout switch. Flame came out of the burners. Lennox says to correct the cause of the rollout trip before anything else: what a rollout switch is telling you.

Smell gas at any point? Leave the house and call from outside.

Older Lennox: count the flashes

Two ways of saying the same thing. Count the flashes on a single light, or read the E code on a display.

Check 1Free, five minutes

Match the flash count

No light. Lennox lists no power to the control, or a control hardware fault. Check the furnace switch, the breaker and the door first.

1 flash. Flame present with the gas valve off. Shut it down, see above.

2 flashes. Pressure switch closed when the inducer is off, usually a stuck switch.

3 flashes. Pressure switch open when the inducer is running. Vent, inducer, drain or tubing.

4 flashes. Primary limit switch open. Airflow, most often a filter.

5 flashes. Rollout switch open.

6 flashes. Pressure switch cycle lockout, the same family as 3 after it has happened too often.

7 flashes. Lockout, the burners failed to light.

8 flashes. Lockout, the burners lost flame too many times. Usually the flame sensor.

9 flashes. Line voltage polarity incorrect. An electrician’s job.

The last five faults. Lennox says a short press of the push button on the control, under five seconds, flashes the last five fault codes, newest first. A press over five seconds clears them.

Newer Lennox: the E codes

Code	What Lennox calls it	Check first
E000	No error in memory	Nothing
E110, E113	Line voltage low, or high	The supply to the furnace
E111	Line power wired in reverse	Electrician
E112, E117	Ground not detected, or poor ground	The earth ground
E115	Low 24 volts	Transformer and added loads
E200	Hard lockout, rollout circuit open	Why flame rolled out
E204, E205	Gas valve miswired, or relay shorted	Technician
E207	Hot surface ignitor sensed open	The ignitor
E223	Low pressure switch failed open	Vent and inducer
E224	Low pressure switch failed closed	The switch
E225, E226	High pressure switch open, or closed	Vent, inducer, switch
E227	Low pressure switch open during ignition or run	Vent and inducer
E228	Inducer calibration failure	Vent system and switch wiring
E229	Ignition on high fire	No action needed
E240	Low flame current	Clean the flame sensor
E241	Flame sensed out of sequence	Shut off the gas
E250	Limit switch circuit open	Airflow and filter
E252	Discharge air temperature too high	Airflow and temperature rise
E270	Soft lockout, no flame current sensed	Gas on, ignitor lighting
E271, E272	Soft lockout, pressure switch	Vent and inducer
E273	Soft lockout, flame failure	Clean the flame sensor
E274	Soft lockout, limit circuit	Airflow and filter
E275	Soft lockout, flame out of sequence	Shut off the gas
E290	Ignitor circuit fault	The ignitor
E292, E295	Blower cannot start, or too hot	Blower motor
E311, E312	Restricted airflow warning	Filter and ducts
E370	Interlock switch open 2 minutes	Door not fully closed

The codes you can often clear yourself

Most Lennox calls fall into four families, and each has a free first check. Soft lockouts retry on their own after an hour.

Check 2

Work the free check for the family

Airflow: 4 flashes, E250, E274, E311, E312. Lennox’s action for E311 and E312 is to check the filter and the duct system, and for E250 it adds blockages and air flow. Change the filter and open every register first: why a furnace overheats and cuts out.

Flame sensor: 8 flashes, E240, E273. Lennox says to clean or replace the sensor and check the unit’s ground: how to clean a flame sensor safely.

Venting: 3 flashes, E223, E227, E271. Lennox’s instruction is to inspect the vent and the combustion air inducer for correct operation and restriction. Snow, ice or a nest in the pipes outside, or a blocked drain trap, are the free checks: the five places to look.

No flame at all: 7 flashes or E270. Lennox says to check the gas flow and that the ignitor is lighting the burner. Make sure the gas is on at the furnace before anything else.

E370: the door. The interlock is the door safety switch. A blower door not pushed fully home causes it.

When it needs a technician

Check 3

Know when to stop

E204, E205 and anything else about the gas valve. Wiring and relay faults on the valve.

E207 and E290. Lennox says to measure the ignitor’s resistance and replace it if it is open or out of range.

E224, E226 and 2 flashes. A pressure switch stuck closed is a part.

E292 and E295. A blower that will not start or is overheating.

Power codes, E110 to E117. Voltage and grounding problems belong to an electrician or a technician with a meter.

Anything that clears and returns. The cheap cause was not the real one.

Questions people ask

What is a soft lockout?

Lennox’s newer controls stop for an hour after too many failed tries, then try again on their own. The furnace is not fixed, it is retrying, and it locks out again for the same reason.

My display shows a blinking dot and nothing else.

That is idle. Lennox describes the decimal blinking once a second as idle mode. An H means gas heat, a C cooling, and an A the airflow setting.

How do I see past codes on the newer control?

Lennox’s newer controls have an Error Code Recall mode on the display, entered with the button on the board. It needs the door off, so it is usually read by the technician.

What does E229 mean?

Lennox says the control switched to lighting on high fire because the low fire pressure switch did not close in time, and that no action is needed.

My thermostat shows a code the furnace list does not have.

Some Lennox thermostats show alerts of their own, which are a different list from the furnace’s E codes. The thermostat’s own menu or manual explains those.

Can I clear a code by switching it off and on?

Often, and it may bring the heat back. Write the code down first, so whoever comes out knows what the furnace said.

Sources: Lennox installation instructions for the ML180UH (507323-01) and SL280UHV (508245-01)