Lennox Furnace Code E208: Pressure Switch Open Fix

Last updated Sep 22, 2026 · By fixme.vip Editorial

Lennox furnace code E208: what it means

Code E208 on a Lennox furnace means the low pressure switch failed to close (stayed open) when the control board expected it to. When your furnace calls for heat, the inducer (draft) motor starts first and pulls combustion air through the heat exchanger and out the vent. That airflow creates a slight vacuum that should snap the pressure switch closed, telling the board it is safe to proceed to ignition.

If the board energizes the inducer but the pressure switch never closes within its allotted time, the sequence stops and E208 is posted. This is a control-safety interlock — it prevents ignition when combustion gases may not be venting properly.

The most common culprits are on the draft and venting side: a weak or failing inducer, a blocked intake or exhaust vent, cracked or disconnected pressure tubing, water backing up from a plugged condensate line, or the pressure switch itself. On multi-stage Lennox furnaces there may be more than one pressure switch (low and high stage); the legend and trip points vary by model and control board, so confirm which switch is flagged against your unit’s installation manual.

On most Lennox boards E208 auto-clears once the switch closes properly on a later attempt. If it keeps failing across retries, the board can hold or escalate to a hard lockout that requires cycling power. Because diagnosis involves testing the switch, inducer, and vacuum inside the cabinet, this is a pro-level repair.

Lennox furnace code E208: common causes, ranked by probability

1. Blocked or restricted vent/intake — Debris, snow, ice, nests, or a sagging vent pipe reduces draft so the switch can’t close.
2. Plugged condensate drain or trap — On condensing (90%+) furnaces, standing water blocks the pressure port or backs up into the tubing.
3. Cracked, kinked, or disconnected pressure tubing — The small hose between the inducer/vent and the switch leaks off vacuum.
4. Weak or failing inducer motor — The motor spins but doesn’t generate enough draft; bearings or windings are worn.
5. Failed pressure switch — The diaphragm sticks open or the switch is out of calibration.
6. Water or ice in the switch or tubing — Condensate collecting in the port or hose (common in cold weather).
7. Loose or corroded wiring at the switch or inducer — Intermittent connection prevents the closed signal from reaching the board.

In practice, a pressure-switch-open fault is usually traced in that order: confirm the inducer actually runs and produces vacuum, then follow the tubing and the vent/drain path for restrictions, and only then test the switch itself. Your unit’s installation and service literature is the authority on the exact sequence and trip points for your model.

How to fix Lennox furnace code E208: safe checks first

These are the only steps a homeowner should attempt:

• Check the thermostat — Confirm it’s set to Heat and the temperature is above the current room reading. Replace the batteries if it’s battery-powered.
• Inspect the air filter — Worth a look as general maintenance, but be clear that a dirty filter is unlikely to cause E208. The low pressure switch watches the combustion-air/draft side, not the circulating air your filter sits in. Replace the filter if it’s dirty, then keep going down this list — don’t stop here.
• Check the breaker/switch — Confirm the furnace breaker is on and the service switch (looks like a light switch near the unit) is on.
• Look at exterior vents — Go outside and check the intake and exhaust termination pipes for snow, ice, leaves, or nests. Clear anything blocking them from the outside.
• Check the condensate drain — On high-efficiency furnaces, look for standing water or a full drain pan. You may clear an accessible clog only in the drain line outside the furnace cabinet, such as at the exterior drain termination. Do not touch the trap or any drain port inside the unit.
• One reset only — If the unit is locked out, cycle power at the breaker once. If E208 returns, stop and call a technician. Do not repeatedly reset.

Do not open the furnace cabinet, remove or bypass the pressure switch, disconnect tubing, or test electrical components. All of that is technician work.

How a technician will diagnose it

A qualified tech will typically:

1. Verify the call for heat and watch the ignition sequence to confirm the inducer energizes.
2. Measure vacuum at the pressure switch with a manometer while the inducer runs, comparing it to the switch’s rated closing pressure (printed on the switch).
3. Inspect the pressure tubing for cracks, kinks, condensate, or disconnection.
4. Test the switch electrically — checking that it closes at the correct vacuum with a multimeter.
5. Inspect the vent and intake end to end for restrictions, sagging, or improper slope.
6. Check the condensate trap and drain for blockage or water backup into the ports.
7. Evaluate the inducer motor — amperage draw, bearing condition, and wheel debris — if vacuum is low but venting is clear.
8. Check wiring and connections at the switch and inducer.

A trustworthy quote will name which specific part failed (switch, inducer, tubing, or a blocked vent/drain) rather than just “replace the pressure switch.”

Symptom, cause and what to do

Lennox furnace code E208 repair cost

Ranges are typical US pricing including parts and labor; your area and model will vary.

• Clearing a blocked vent or intake: $0 DIY (exterior) to $120–$250 if a tech must disassemble/reroute.
• Clearing condensate line/trap: $0–$25 DIY to $100–$200 professional.
• Replacing pressure tubing: $100–$200.
• Pressure switch replacement: $150–$350 (part $30–$90 plus labor).
• Inducer motor replacement: $400–$1,200 installed, depending on model and assembly. Condensing (90%+) furnace inducer assemblies commonly land in the upper half of that range, so a quote near $900 is not automatically out of line.
• Diagnostic/service call: $90–$180, often credited toward the repair.

If your unit is under Lennox warranty, the pressure switch or inducer part may be covered—confirm registration and keep labor separate in the quote.

Related codes

The code legend varies by control board, so always confirm a code’s meaning in the installation or service manual for your specific model before acting on it. Two codes commonly listed alongside E208 in the pressure-switch group:

• Code E223 — pressure switch failed to open.
• Code E224 — high pressure switch failed to close.
• Code E125 — Lennox Furnace Code E125: control board failure.

If a code on your board points to a rollout switch or any other combustion-safety lockout, that is never a homeowner troubleshooting item — shut the furnace off and call a licensed technician.

If your furnace also shows ignition or flame-proving codes alongside E208, address the venting/pressure-switch fault first—restoring proper draft often clears downstream ignition faults.