The short answer
E150 on a Lennox furnace in Northern Virginia means the refrigerant leak sensor at the indoor coil detected refrigerant. Newer Lennox systems use R-454B, a mildly flammable refrigerant, and they’re built to handle a leak on their own: the indoor fan comes on to mix it into the house air, and the compressor and any electric heat shut off. Leave the fan running and call. The alarm won’t clear while the sensor still detects refrigerant.
Why your system has a leak sensor at all
The refrigerant in AC systems changed. New systems use refrigerants like R-454B, which ASHRAE rates A2L: lower toxicity and lower flammability, with a slow burning speed. Because it can burn, the safety standard for this equipment, UL 60335-2-40, requires a leak detection system. The sensor sits low in the indoor unit near the coil, where leaked refrigerant collects.
When the sensor reads refrigerant at a quarter of the level where it could burn, the system typically reacts within 15 seconds: blower on, compressor and electric heat off. That’s what you’re seeing. More on the refrigerant itself in R-454B refrigerant.
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What Lennox says the leak codes mean
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| Code | What Lennox says | What it means for you |
|---|---|---|
| E150 | Refrigerant leak detected | A leak at or in the indoor coil. Can’t clear while the sensor reports a leak. The charge needs checking. |
| E151, E152 | Refrigerant leak detector sensor fault | The sensor itself failed, sensor 1 or 2. It may need replacing. |
| E154, E155 | Sensor communication lost | The wire or connector to the sensor. The blower stays on at least 5 minutes after it comes back. |
| E160, E161 | Sensor type incorrect | The wrong sensor was installed. Lennox says to use its approved part. |
| E164 | Low GWP test | Someone pressed the test button. Clears after a minute. |
| E390 | Low GWP relay stuck | A relay on the board. May need a board. |
On an S30 or S40 thermostat, the same leak shows as alert 150, refrigerant leak detected (Lennox S40 alerts).
What to do right now
Let the fan run. The blower running on its own is the system doing its job. Turning the power off stops the fan that’s clearing the refrigerant.
Open a couple of windows near the furnace if you can. Keep open flames and sparks away from the furnace area until it’s checked.
Check the test button. If anyone was near the furnace and you see E164, not E150, it’s the test mode, and it clears in a minute.
Call the same day. A leak alarm means the system is low on refrigerant, or will be, and it won’t cool or heat with a heat pump until the leak is fixed.
Why indoor coils leak
Indoor coils leak at brazed joints, at the fittings, and from corrosion that eats tiny holes in the tubing over the years. A false alarm happens too: a failing sensor (E151) or a strong chemical smell near the furnace, like paint or cleaners, can set one off. A tech confirms with an electronic leak detector before anyone talks about parts.
What it costs
The diagnostic is a flat $99. Recharging after a fix runs $190 to $740 at our prices. The leak repair itself gets priced in writing once we’ve found it, because one loose fitting and a whole coil are very different jobs. If the coil is the problem and the system is older, we’ll give you both numbers, repair and replace.
If the repair is a big one on an older system, get a second look before you spend it. Our free second opinion costs you nothing, and the estimator shows what a new system costs with $1,500 off already in the price. Thinking about brands? Lennox vs Trane lays out the difference.
Every Lennox code in one place: Lennox error codes.
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Call or book a Lennox repair
Call (703) 997-9757. We answer day or night. Or book online and pick a time. The diagnostic is a flat $99, and you see the repair price in writing before we touch anything. Furnace running fine and you want to keep it that way? Book the $67 heating check from goswiftpro.com/cookiesoffer (book by November 30) and a box of warm cookies comes with the visit. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276. More on Lennox repair in Northern Virginia.
Questions people ask
What does E150 mean on a Lennox furnace?
The refrigerant leak sensor at the indoor coil detected refrigerant. The system turns the blower on and shuts off the compressor and electric heat. It can’t be cleared while the sensor still reads a leak.
Is a Lennox refrigerant leak alarm dangerous?
The refrigerant, R-454B, is rated lower flammability, and the system is built to react within seconds by running the fan. Let the fan run, keep flames and sparks away, open a window, and have it checked the same day.
Why is my Lennox furnace fan running by itself?
If the code is E150, the leak sensor detected refrigerant and the fan is mixing it into the house air, which is what it’s designed to do. Leave it on.
What does E151 mean on a Lennox?
The refrigerant leak detector sensor has a fault. The sensor itself or its wiring needs checking, and it may need replacing.
