🌡️Heat Pump

ALERT 73

Lennox · XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump

Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump ALERT 73 Error Fix: Outdoor Coil Temperature Sensor Fault

Outdoor coil temperature sensor is out of range. In heat pump mode, critical for defrost cycle initiation. Faulty sensor can cause failure to defrost (ice accumulation) or defrost too frequently (reduced efficiency). Check sensor position, wiring, and electrical readings.

Medium severity2 fixes available✨ Free fix available

Quick Answer

Error ALERT 73 on the Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump means: Outdoor Coil Temperature Sensor Fault. The top-ranked community fix is “Replace Outdoor Coil Temperature Sensor and Test Wiring” (medium difficulty, ~45 min, DIY cost: $15-$25). 2 community-ranked fixes available below.

Published February 2026 · 2 fixes · heat pump

Content is based on manufacturer service documentation, community repair experience, and OEM technical bulletins. Always verify with your owner's manual.Learn about our editorial standards.

When to Call a Professional

While many heat pump repairs can be done safely at home, consider hiring a qualified technician if:

The repair involves electrical wiring, gas lines, or refrigerant
You've tried the top-ranked fix and the error persists
You smell gas, see sparking, or notice water leaking
The repair requires specialized tools you don't have
Your appliance is still under manufacturer warranty

Average professional repair cost for this issue: $120-$180.

Other Lennox Models with Error ALERT 73

XC21 Dave Lennox Signature Collection 21 SEER Variable-Capacity Air Conditioner

air_conditioner · 2 fixes

XC25 Dave Lennox Signature Collection 26 SEER Variable-Capacity Air Conditioner

air_conditioner · 2 fixes

XP21 Dave Lennox Signature Collection 20 SEER Heat Pump

heat_pump · 2 fixes

Other Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump Error Codes

1 FLASH YELLOW

High Pressure Switch Open

2 fixes

2 FLASHES YELLOW

Low Pressure Switch Open

2 fixes

3 FLASHES YELLOW

Compressor Thermal Overload

2 fixes

4 FLASHES YELLOW

Short-Cycle Protection

2 fixes

ALERT 1

Communication Loss — Outdoor Unit

2 fixes

ALERT 11

High Pressure Protection — Outdoor Unit

2 fixes

ALERT 12

Low Pressure Protection — Outdoor Unit

2 fixes

ALERT 14

Compressor Discharge Temperature High

2 fixes

People Also Ask About Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump Error ALERT 73

What does error code ALERT 73 mean on a Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump?

Error code ALERT 73 on the Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump means: Outdoor Coil Temperature Sensor Fault. Outdoor coil temperature sensor is out of range. In heat pump mode, critical for defrost cycle initiation. Faulty sensor can cause failure to defrost (ice accumulation) or defrost too frequently (reduced efficiency). Check sensor position, wiring, and electrical readings.

How do I fix error code ALERT 73 on my Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump?

The most successful fix is "Replace Outdoor Coil Temperature Sensor and Test Wiring" (medium difficulty, ~45 minutes). Estimated DIY cost: $15-$25. HomeMD has 2 community-ranked fixes for this error.

Is error code ALERT 73 on a Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump serious?

This error is rated medium severity. It should be addressed soon, but your appliance may still function in a limited capacity.

Can I fix Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump error ALERT 73 myself?

Yes — the top-ranked community fix ("Replace Outdoor Coil Temperature Sensor and Test Wiring") is rated medium difficulty and takes about 45 minutes. Tools needed: T20 Torx screwdriver, Multimeter, Needle nose pliers.

How much does it cost to repair Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump error ALERT 73?

DIY cost: $15-$25. Professional repair typically costs $120-$180. Many homeowners save money by trying the top-ranked community fix first.

What other error codes does the Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump have?

The Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump has 8 other known error codes, including: 1 FLASH YELLOW (High Pressure Switch Open), 2 FLASHES YELLOW (Low Pressure Switch Open), 3 FLASHES YELLOW (Compressor Thermal Overload), 4 FLASHES YELLOW (Short-Cycle Protection), ALERT 1 (Communication Loss — Outdoor Unit), and 3 more.

Which other Lennox models have the ALERT 73 error?

Error code ALERT 73 also appears on 3 other Lennox models: XC21 Dave Lennox Signature Collection 21 SEER Variable-Capacity Air Conditioner, XC25 Dave Lennox Signature Collection 26 SEER Variable-Capacity Air Conditioner, XP21 Dave Lennox Signature Collection 20 SEER Heat Pump. The fix may vary by model, so check each model's specific page for tailored repair steps.

What other error codes does the Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump have?

The Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump has 8 other known error codes:

1 FLASH YELLOW — High Pressure Switch Open (2 fixes)
2 FLASHES YELLOW — Low Pressure Switch Open (2 fixes)
3 FLASHES YELLOW — Compressor Thermal Overload (2 fixes)
4 FLASHES YELLOW — Short-Cycle Protection (2 fixes)
ALERT 1 — Communication Loss — Outdoor Unit (2 fixes)
ALERT 11 — High Pressure Protection — Outdoor Unit (2 fixes)
ALERT 12 — Low Pressure Protection — Outdoor Unit (2 fixes)
ALERT 14 — Compressor Discharge Temperature High (2 fixes)

Which other Lennox models have the ALERT 73 error?

Error code ALERT 73 also appears on 3 other Lennox models:

XC21 Dave Lennox Signature Collection 21 SEER Variable-Capacity Air Conditioner (air conditioner) · 2 fixes
XC25 Dave Lennox Signature Collection 26 SEER Variable-Capacity Air Conditioner (air conditioner) · 2 fixes
XP21 Dave Lennox Signature Collection 20 SEER Heat Pump (heat pump) · 2 fixes

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