🌡️Heat Pump

ALERT 1

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

Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump ALERT 1 Error Fix: Communication Loss — Outdoor Unit

The iComfort thermostat has lost communication with the outdoor unit (AC or heat pump). The communicating bus uses a 4-wire connection (R, C, S1, S2). Check wiring between thermostat, indoor unit, and outdoor unit. Verify outdoor unit control board has power. Lightning strikes and power surges commonly damage communicating circuits.

High severity2 fixes available✨ Free fix available

Quick Answer

Error ALERT 1 on the Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump means: Communication Loss — Outdoor Unit. The top-ranked community fix is “Test and Replace Outdoor Unit Control Board” (hard difficulty, ~90 min, DIY cost: $0). 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:

This is a high severity error — continued use may cause damage or a safety hazard
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: $250-$400.

Other Lennox Models with Error ALERT 1

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 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

ALERT 2

Communication Loss — Indoor Unit

2 fixes

People Also Ask About Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump Error ALERT 1

What does error code ALERT 1 mean on a Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump?

Error code ALERT 1 on the Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump means: Communication Loss — Outdoor Unit. The iComfort thermostat has lost communication with the outdoor unit (AC or heat pump). The communicating bus uses a 4-wire connection (R, C, S1, S2). Check wiring between thermostat, indoor unit, and outdoor unit. Verify outdoor unit control board has power. Lightning strikes and power surges commonly damage communicating circuits.

How do I fix error code ALERT 1 on my Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump?

The most successful fix is "Test and Replace Outdoor Unit Control Board" (hard difficulty, ~90 minutes). This fix costs nothing. HomeMD has 2 community-ranked fixes for this error.

Is error code ALERT 1 on a Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump serious?

This error is rated high severity. You should address it promptly — continued use could cause damage or safety concerns.

Can I fix Lennox XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump error ALERT 1 myself?

Yes — the top-ranked community fix ("Test and Replace Outdoor Unit Control Board") is rated hard difficulty and takes about 90 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 1?

DIY cost: $0. Professional repair typically costs $250-$400. 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 11 (High Pressure Protection — Outdoor Unit), and 3 more.

Which other Lennox models have the ALERT 1 error?

Error code ALERT 1 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 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)
ALERT 2 — Communication Loss — Indoor Unit (2 fixes)

Which other Lennox models have the ALERT 1 error?

Error code ALERT 1 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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