Goodman AC & Heat Pump Error Code L8: Meaning & How to Fix It

By the ErrorCodePro Editorial Team · Last reviewed October 20, 2026

Goodman ac & heat pump error code L8 means: Low line voltage: the control detects supply voltage below the rating-plate range. [1] Keep using it? Only if the code clears after the owner checks; if it returns, leave the system off and call an HVAC technician. Start with the owner checks below, beginning with: check breakers and the outdoor disconnect.

Source: Goodman GSXC7 installation instructions, unitary diagnostic codes, via Alpine Home Air (manual copy) [1].

Quick facts

Code	L8
Also shown as	None listed by the manufacturer
Brand / appliance	Goodman ac & heat pump (gsxc7 variable-speed air conditioners (7-segment diagnostic display))
System	Power supply
Meaning (service chart)	Low line voltage: the control detects supply voltage below the rating-plate range. [1]
Keep using it?	Only if the code clears after the owner checks; if it returns, leave the system off and call an HVAC technician
DIY-safe?	Owner checks only (listed below)
Support	Goodman dealer or Goodman customer support (goodmanmfg.com)
Source document	Goodman GSXC7 installation instructions, unitary diagnostic codes (via Alpine Home Air (manual copy))

On this page: Meaning · Steps · Parts · When to call a technician · Related codes · FAQ

What error code L8 means on a Goodman ac & heat pump

Low line voltage: the control detects supply voltage below the rating-plate range. [1]

This is a power supply code. Codes and wording can vary by model, so check your owner's manual for your model number.

How to fix Goodman ac & heat pump error code L8 (safe owner checks)

Owner checks only: on heating, cooling and water-heating equipment, limit yourself to reading the code and checking the thermostat, breaker and service switch, air filter, condensate drain, that the gas supply valve is open (no disassembly) and that vent terminals are clear of snow or debris. Reset power only if your manual allows it.

Safety first: disconnect power before you remove any panel or reach into the sump or drum. Do not touch wiring, the control board or the motor. If you see water near electrical parts, stop and call a technician. These steps are based on the Goodman GSXC7 installation instructions, unitary diagnostic codes (via Alpine Home Air (manual copy)) [1], rewritten for clarity.

Check breakers and the outdoor disconnect. At the main panel, make sure the AC/heat pump breaker is fully on, and that the disconnect switch beside the outdoor unit is on. Do not open the unit's electrical panel.
Note other symptoms. If lights dim or other large appliances struggle at the same time, the supply voltage may be low; the manual says to contact the local utility if needed.
Restart and watch. Restore power, set the thermostat back to cooling or heating and check whether code L8 returns. If it does, call an HVAC technician; the remaining causes need gauges, meters or refrigerant work.

Owner steps are general safe checks added by ErrorCodePro; the manual's own corrective actions are technician procedures and are listed under When to call a technician.

Parts that may be involved

Exact parts depend on your model number. This page lists part types only, never part numbers.

No specific part is implied by the manufacturer's guidance for this code.

When to call a technician

Voltage at the unit must be measured by a licensed electrician or HVAC technician
Gas valves, burners, igniters, flame sensors, venting/flue or CO concerns: licensed HVAC technician or plumber
Refrigerant work: EPA 608-certified technician only
Smell of gas: leave and call the gas utility or 911
Anything involving wiring, the control board, the motor or the water valve electrics
The appliance is under warranty: contact Goodman dealer or Goodman customer support (goodmanmfg.com) first

Frequently asked questions

What does error code L8 mean on a Goodman ac & heat pump?

The Goodman GSXC7 installation instructions, unitary diagnostic codes lists L8 as follows: Low line voltage: the control detects supply voltage below the rating-plate range.

Is it safe to keep using the ac & heat pump with L8?

Only if the code clears after the owner checks; if it returns, leave the system off and call an HVAC technician.

Can I fix Goodman ac & heat pump error L8 myself?

Only with the owner checks on this page, starting with: check breakers and the outdoor disconnect. If it persists, call a technician or Goodman dealer or Goodman customer support (goodmanmfg.com).

Sources

Alpine Home Air (manual copy): Goodman GSXC7 installation instructions, unitary diagnostic codes (third-party copy of manufacturer service data)

Last reviewed: October 20, 2026. ErrorCodePro is not affiliated with Goodman.