Lennox Furnace Error Code E016 usually means the furnace control has detected a low-pressure switch circuit problem, most often caused by a blocked condensate drain, restricted intake or exhaust vent, or a stuck pressure switch. The single most likely fix is to clear the condensate tubing and venting, then reset power and confirm the pressure switch closes properly during inducer operation.

⚡ Quick Fix

1. Turn the furnace off at the disconnect or breaker, or unplug it if it uses a cord connection. Wait 15 to 30 minutes so the control board can fully reset, then restore power and call for heat at the thermostat. If the code returns immediately, the fault is active and not just a temporary lockout.
2. The most common real fix is clearing a blocked condensate trap, drain hose, intake pipe, or exhaust vent. A Lennox condensing furnace depends on proper inducer draft and pressure switch operation, and even partial blockage from water, debris, ice, or sludge can trigger E016. After clearing the restriction, restart the unit and watch for normal ignition.
3. If the reset and airflow path check do not solve it, inspect the pressure switch tubing, wiring harness, and inducer assembly. Cracked tubing, loose spade terminals, a weak inducer motor, or a failing PCB input can all prevent the pressure switch signal from reaching the control correctly. Stop if you are not comfortable using a multimeter around live furnace circuits.

What This Error Means

On many Lennox furnace platforms, Lennox Furnace Error Code E016 points to a draft-proving issue in the pressure switch circuit. The pressure switch is a safety device that verifies the inducer motor is creating the correct negative pressure before the hot surface ignitor, gas valve, and burners are allowed to operate. If the switch stays open when it should close, opens during a heating cycle, or sends an unstable signal to the control board, the furnace locks out and posts E016.

This does not automatically mean the pressure switch itself is defective. In the field, the actual cause is often external to the switch: a clogged condensate trap, water in the pressure tubing, a partially blocked flue, a plugged intake, or an inducer wheel that is not pulling enough draft. Loose wiring, corroded terminals, and a damaged wiring harness between the pressure switch and PCB can also create the same fault signature.

Because the pressure switch is part of the combustion safety circuit, E016 should be treated seriously. Bypassing the switch, jumping wires, or forcing the furnace to run is unsafe and can allow improper venting, flame rollout risk, or carbon monoxide hazards. The goal is to find out why the switch is not proving draft, not to defeat the safety circuit.

Common Causes

Blocked condensate drain or trap

High-efficiency Lennox furnaces produce condensate that must drain freely through the trap and tubing. If the trap fills with sludge or the hose kinks, water backs up into the inducer housing or pressure tubing and the switch cannot read pressure correctly. This is one of the most common causes of E016.

Restricted intake or exhaust vent

Leaves, nests, snow, ice, and even sagging vent sections can reduce airflow through the combustion system. When the inducer cannot establish proper draft, the pressure switch stays open or drops out during operation. A vent restriction may be intermittent, especially during wind, freezing conditions, or heavy rain.

Faulty pressure switch or damaged tubing

The switch diaphragm can weaken with age, and the port can plug with condensate residue. The rubber or vinyl tubing may split, collapse, or fill with water, causing a false pressure reading. A pressure switch problem should be confirmed with testing, not guessed.

Inducer motor or wheel problem

A weak inducer motor, damaged capacitor on applicable designs, or debris on the inducer wheel can reduce draft enough to trigger the error. Sometimes the motor runs but does not reach the required speed under load. Bearing wear and water intrusion are also common failure points.

Loose wiring or control board issue

If the wiring harness between the pressure switch and control board has loose spade connectors, corrosion, or broken conductors, the board may read the switch state incorrectly. In rarer cases, the furnace PCB input circuit fails and reports a pressure switch fault even when the switch and draft are normal. Electrical diagnosis is needed before replacing a board.

Step-by-Step Fix

Tools you may need: screwdriver, multimeter, flashlight

Safety warning: Disconnect power before opening any panels or touching internal components.

1. Start with a full power reset and a visual inspection. Shut off power to the furnace for 15 to 30 minutes, then remove the access panels and look for standing water, disconnected tubing, burnt wire terminals, or obvious vent blockage. Restore power and call for heat while listening for the normal sequence: inducer starts, pressure switch proves, ignitor glows, gas valve opens, burners light, then blower starts.
2. Check the intake and exhaust venting from the furnace all the way to the outside termination. Remove leaves, lint, insect nests, snow, or ice, and make sure no screen or termination cap is obstructed. If the vent pipes sag and hold water, or if you see water dripping back toward the furnace, correct that issue before restarting.
3. Inspect and clean the condensate system. Disconnect the condensate trap and drain hoses if accessible, flush out sludge, and make sure water can move freely to the drain. Also inspect the pressure switch tubing for moisture, cracks, splits, or pinched sections; if water is present in the tube, dry it and identify why condensate is backing up.
4. Examine the pressure switch and wiring harness closely. Make sure the switch port is not clogged and the tubing fits tightly at both ends. Check the spade connectors at the pressure switch, inducer, and control board for looseness or corrosion, and reseat them if needed with power off.
5. Test the inducer operation. When the thermostat calls for heat, the inducer should start promptly and sound smooth, not strained, rattling, or weak. If it hums, stalls, cycles erratically, or fails to move enough air, the motor, wheel, capacitor on certain designs, or inducer housing may be at fault and should be professionally evaluated.
6. Use a multimeter only if you are qualified to do so. With the furnace energized and calling for heat, a technician can verify whether the pressure switch closes when draft is established and whether continuity is stable through the switch circuit. If draft is correct but the switch does not close, the switch may be defective; if the switch closes but the board still shows E016, the wiring harness or PCB may be failing.
7. Stop and call a professional if you smell gas, see signs of vent leakage, find repeated condensate flooding, or the code returns after you clear drains and vents. You should also stop if testing points to the inducer assembly, gas valve sequence, or control board. Combustion analysis and pressure measurements are often required to finish the diagnosis safely.

Related Errors

• Error E200 — Indicates a rollout switch or high-temperature safety circuit issue that has opened and shut down burner operation.
• Error E201 — Points to a blower motor communication or operation fault that can prevent proper airflow through the heat exchanger.
• Error E223 — Signals a low-pressure switch did not close or opened unexpectedly during the call for heat.
• Error E225 — Indicates the pressure switch remained closed when it should have been open at the start of the heating cycle.
• Error E228 — Refers to ignition proving trouble, often involving flame sensing or burner light-off failure.

FAQ

Can I reset this error without a technician?

Yes, you can try a basic reset by shutting off furnace power for 15 to 30 minutes and then restoring power. If Lennox Furnace Error Code E016 was caused by a temporary lockout, it may clear. If the code comes back, the furnace still detects a pressure switch or draft problem that needs inspection.

Is it safe to run my furnace with E016 showing?

No. E016 involves the combustion safety circuit, so the furnace should not be forced to run. The pressure switch is there to confirm proper venting and inducer draft before ignition. If that circuit is bypassed or ignored, the unit may vent improperly and create a serious safety hazard.

What is the most common repair for Lennox Furnace Error Code E016?

The most common repair is clearing a blocked condensate trap or drain line and removing any intake or exhaust vent obstruction. Those two issues often prevent the pressure switch from proving draft even though the switch itself is still good. A cracked pressure tube is another common and inexpensive fix.

How much does it cost to fix?

Cost depends on the cause. A simple condensate cleaning, tubing repair, or vent clearing is usually on the low end. Replacing a pressure switch is moderate, while an inducer motor assembly or PCB diagnosis and replacement costs more. The final price depends on labor, access, and whether multiple faults are present.

Can a dirty filter cause E016?

Usually not directly. A dirty air filter more often causes overheating or limit switch faults because it restricts supply airflow, not combustion draft. However, multiple airflow and drainage problems can occur at the same time, so it is still smart to replace a heavily clogged filter while troubleshooting the furnace.

When should I call a professional?

Call a professional if you have cleared the drain and venting, inspected the tubing and wiring, and E016 still returns. You should also call immediately if the inducer sounds abnormal, water keeps backing up, you suspect a cracked vent, or you are not comfortable testing live electrical circuits with a multimeter.