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Lennox

OEM Lennox Pressure Switch — 18L21

SKU: LNX-18L21 Brand: Lennox
$24.95 $34.95

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Texas CMBL #19328542014
SAM.gov Registered
Govt POs Accepted

The Lennox 18L21 is a genuine OEM pressure switch designed to monitor the negative pressure created by the draft inducer motor in your Lennox furnace, ensuring safe and efficient combustion. If this switch fails, you may experience symptoms such as the furnace failing to ignite, short cycling, or a blinking error code indicating a pressure switch fault. This direct OEM replacement is compatible with select Lennox gas furnace models and ensures a precise fit for reliable, long-term performance.

Shipping Information

  • Orders placed before 3PM CST ship same business day
  • Standard delivery: 2-5 business days
  • Express shipping available at checkout
  • Free shipping on orders over $75
  • Tracking number emailed upon shipment

Return Policy

  • 30-day returns on unused parts in original packaging
  • Electrical parts (capacitors, contactors, control boards) are final sale once installed
  • Email info@nationalhvacparts.com to initiate a return
  • Refunds processed within 5-7 business days

Frequently Asked Questions

Does this Pressure Switch fit my Lennox OEM Lennox Pressure Switch — 18L21?
Yes. This is the factory-specified OEM pressure switch for the Lennox OEM Lennox Pressure Switch — 18L21. It is a direct drop-in replacement that fits without modification. Always verify the model number on your equipment nameplate before ordering.
How do I replace the pressure switch on my Lennox OEM Lennox Pressure Switch — 18L21?
Difficulty: Medium (20–30 min)
Step 1: Turn off power. Step 2: Locate pressure switch near draft inducer. Step 3: Note tubing orientation. Step 4: Disconnect tubing and wires. Step 5: Remove screw, install new switch. Step 6: Reconnect tubing and wires, restore power.
My furnace shows a pressure switch error. What do I replace?
Furnace LED showing pressure switch error = switch not detecting draft inducer airflow. Try first: clear the rubber tubing to the switch (often clogged with condensation). If problem persists, replace the pressure switch.
Is this pressure switch compatible with Bryant or Payne too?
Many Lennox parts are cross-compatible with Bryant and Payne since all three brands are manufactured by Carrier Global Corporation. The same physical part is often used across brand labels with different model numbers. To verify: check your Bryant or Payne equipment service manual for cross-compatible part numbers, or email info@nationalhvacparts.com with your model number.
Should I use OEM or aftermarket for my Lennox pressure switch?
OEM recommended for reliability and warranty compatibility. OEM parts match exact factory specifications for proper fit, performance, and safety. While aftermarket alternatives cost less upfront, the risk of improper fit and reduced lifespan usually makes OEM the better value long-term.
How fast does National HVAC Parts ship?
Orders placed before 3:00 PM CST ship the same business day. Standard delivery is 2–5 business days anywhere in the continental United States. Express shipping available at checkout. We ship from Houston, TX to all 50 states. 30-day return policy on all parts.
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Mike Rivera
HVAC Parts Specialist — Online