Lennox Furnace Red and Green Light Flashing Together — Diagnosis & Repair in Greater Vancouver

Seeing both a red and a green light flashing on your Lennox furnace — sometimes together, sometimes alternating — is one of the more confusing things a control board can show, because it looks like two messages at once. In most cases that is exactly what it is: the green LED is doing its normal status job while the red LED reports a fault, or the board is using a two-colour or two-part pattern to communicate a combined condition. The green side is usually reassurance that the board has power; the red side is the part that needs your attention.

ROMA Heating & Cooling repairs Lennox furnaces across Vancouver, Burnaby and Richmond, and this page explains how to make sense of a red-and-green display, how to read a two-part code, and when to call. Before anything: a gas smell or CO alarm overrides all of this — leave and call 911 and FortisBC from outside.

What red and green flashing together means on your Lennox furnace

On Lennox boards, simultaneous red and green activity generally comes down to one of these:

• Status plus fault. Green keeps pulsing to show the board is alive while red flashes an active fault code. The two are separate messages happening at once.
• A two-part combined code. Some boards use a sequence that involves both colours, or a slow-then-fast rhythm, to express a single condition. Each part is counted separately.
• Two LEDs on one board. Certain Lennox controls have more than one indicator, and reading them side by side gives the full picture.

The important takeaway: the presence of red means there is a fault to resolve. Green alone would be benign; red-and-green together still points to something the furnace wants fixed.

How to read a two-colour Lennox code

📞 Talk to a licensed ROMA furnace technician — (604) 704-0300

• Watch a full cycle and note which colour flashes first and how many times each colour flashes.
• If the board uses a slow set then a fast set, count each set separately — that pair is the code.
• Ignore the green “heartbeat” if it is a steady even pulse; focus on the red count as the fault.
• Open the blower door and match the pattern to the legend on the label, or the installation manual.

Do not assume a specific meaning from a generic online chart. Lennox two-colour patterns differ by board generation, and the same red count can mean different things on different models. Record the pattern and verify against your manual, or read it to a technician.

The common faults a red-and-green pattern points to

Because red is present, the underlying fault is usually one of the standard furnace categories:

Flame-proving or ignition fault

The furnace tried to light but did not confirm flame. Safe check: confirm the gas is on and the filter is clean, allow one reset.

Pressure-switch / venting fault

A blocked vent or full condensate trap, common on high-efficiency furnaces in our wet climate. Safe check: clear the condensate line and outside vent.

High-limit / airflow fault

Overheating from a dirty filter or restricted airflow. Safe check: replace the filter and open the vents.

Control-board or wiring condition

A polarity, grounding or board fault. This needs a technician with a meter.

Red-and-green quick reference

Safe things to try once

• Thermostat set to heat with fresh batteries; setpoint above room temperature.
• Furnace switch and breaker on; blower door fully closed so the door switch engages.
• Clean 1" filter; supply registers open; gas valve open.
• Clear the condensate trap and line.
• Cycle power once to clear a lockout and let it try again.

If the red keeps flashing after one reset, stop and call ROMA at (604) 704-0300 with the exact colour sequence and counts.

When it is an emergency

Escalate immediately for a gas smell, a CO alarm, soot near the burners, or no heat in a cold snap with a vulnerable household — call us for priority scheduling or 911 for a suspected leak. Otherwise a red-and-green code is a diagnose-then-repair situation.

What ROMA checks on a two-colour Lennox pattern

A red-and-green display tells us to separate the status from the fault. We confirm the green pulse is the normal heartbeat, then focus entirely on the red count, verifying it against the board legend and our own reading of the sequence. From there it is standard fault work: we test the flame sensor, igniter, pressure switch and gas valve, and check polarity and ground. The two-colour display can look alarming, but once we isolate the red message it usually resolves to a familiar, repairable fault.

Vancouver homes and multi-indicator boards

Some Lennox systems in Coquitlam and Port Moody homes we service use boards with more than one indicator, so reading them side by side is part of the job. We have seen homeowners chase the green light thinking it was the problem, when the green was simply confirming the board had power. Knowing which light is talking saves time and parts.

Prevention and what to expect

As with any red-code fault, a clean flame sensor, clear venting and a clear condensate path prevent most recurrences. Repairs are typically a single component, quoted flat-rate after diagnosis, and we confirm the two-colour pattern has cleared before we leave.

Safety comes before the code

A two-colour display can be unsettling, but your response to a gas or CO event is unchanged: a gas smell means leave the home and call FortisBC and 911 from outside, and a CO alarm or anyone feeling unwell means get everyone out and call 911. Never bypass the safety behind a red code to keep the furnace running. Read the pattern, do the safe checks, and let a licensed technician handle anything internal.

What to have ready and how we help

The most useful thing you can tell us at (604) 704-0300 is the sequence: which colour flashes first, how many times each colour flashes, and whether they alternate or overlap. A short phone video is even better. Have the model number handy if you can reach the label. ROMA has read Lennox codes across Greater Vancouver since 1999, backed by upfront flat-rate pricing, 0% financing on approved credit, and service seven days a week in Vancouver, Burnaby, Richmond, Surrey, Coquitlam, Port Moody and the North Shore.

Red-and-green compared with the single-colour signals

A two-colour display makes more sense once you see it as two of the single-colour signals happening at once. On their own, green means status and red means fault; together they usually mean “the board is powered (green) and also reporting a fault (red).” That is why the response is not to panic at the combination but to separate them — note the green as reassurance and read the red as the actual problem to solve.

Leaving the red half of a two-colour code unaddressed has the same consequence as any red fault: the furnace keeps locking out and the underlying flame, venting or airflow issue tends to worsen. In a Vancouver winter that risks a full no-heat failure, so reading the red count and booking a repair early is the smart move.

The bottom line on a red-and-green Lennox

Two colours at once looks alarming but usually just means “powered and reporting a fault.” Treat the green as reassurance and the red as the real message: count the red, match it to your legend, and do the safe checks. Once the red is isolated, it almost always resolves to a familiar flame, venting or airflow fault. ROMA reads the pattern and repairs the underlying issue across Greater Vancouver so both lights return to normal.

Why ROMA for Lennox in Vancouver

Two-colour Lennox codes can look alarming but usually resolve to a familiar flame, venting or airflow fault once read correctly — the everyday work of ROMA Heating & Cooling. We are TSBC-licensed (Gas licence LGA0202903), bonded, insured, Red Seal-trained and rated 4.8★ from 221 Google reviews, with upfront flat-rate pricing seven days a week. Book a furnace repair or a free-estimate visit, or use our furnace hub to learn how to read the code. Serving Vancouver, Burnaby, Richmond, Surrey, Coquitlam, Port Moody and the North Shore — call (604) 704-0300.

Frequently Asked Questions

What does it mean when my Lennox furnace flashes red and green together?

Usually the green LED is a normal status pulse while the red LED reports an active fault, or the board is using a two-part combined code. The green side means the board has power; the red side is the fault to read against your door legend and repair.

How do I read a red-and-green code on a Lennox furnace?

Watch a full cycle, note which colour flashes first and how many times each flashes. If it uses a slow set then a fast set, count each separately. Focus on the red count as the fault, then match it to the legend inside the blower door.

Is a red and green flashing Lennox furnace dangerous?

Not necessarily, but the red means there is an active fault to resolve. It becomes urgent if you smell gas, a CO alarm sounds, or you see soot. Do the safe basic checks, reset once, and call a licensed technician if the red keeps flashing.

Why would only the red light remain after green stops on my Lennox furnace?

The fault is taking priority over the status pulse. Note the red flash count, run the safe checks like filter, gas and door switch, and have a licensed technician read the exact code, since counts vary by Lennox board generation.

Can ROMA diagnose a two-colour code on my Lennox furnace in Vancouver?

Yes. ROMA is a TSBC-licensed gas contractor serving Greater Vancouver that reads Lennox two-colour codes and repairs the underlying flame, venting or airflow fault, with flat-rate pricing seven days a week. Call (604) 704-0300.

Reviewed by the ROMA Heating & Cooling team — TSBC-licensed gas contractor (Gas LGA0202903), serving Greater Vancouver since 1999. Updated July 2026.

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