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Lennox

OEM Lennox 3/4" Union Sweat Thermostatic Mixing Valve — X6440

SKU: LNX-X6440 Brand: Lennox
$39.95 $54.95

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Texas CMBL #19328542014
SAM.gov Registered
Govt POs Accepted

The Lennox X6440 is a genuine OEM 3/4-inch union sweat thermostatic mixing valve designed for compatible Lennox hydronic and water heating applications, automatically blending hot and cold water supplies to deliver a consistent, controlled outlet temperature and prevent scalding. Signs that this valve may need replacement include fluctuating water temperatures, failure to reach set temperature, or water that is excessively hot or cold at the outlet. This factory-original Lennox replacement valve is built to precise specifications for a reliable sweat-connection installation in applicable Lennox systems.

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 Thermostat fit my Lennox OEM Lennox 3/4" Union Sweat Thermostatic Mixing Valve — X6440?
Yes. This is the factory-specified OEM thermostat for the Lennox OEM Lennox 3/4" Union Sweat Thermostatic Mixing Valve — X6440. 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 thermostat on my Lennox OEM Lennox 3/4" Union Sweat Thermostatic Mixing Valve — X6440?
Refer to your equipment service manual for model-specific steps. General approach: turn off power, photograph connections, remove old part, install new part, restore power and test. For gas components, hire a licensed technician. Email info@nationalhvacparts.com for guidance.
What symptoms mean I need a new thermostat?
Common symptoms: unusual noises, intermittent operation, complete failure, or visible damage. Visit our diagnostic hub for symptom-based troubleshooting.
Is this thermostat 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 thermostat?
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