Error Code 4 Flashes
High

Amana AMSS960803BN Error Code 4 Flashes: Primary or Auxiliary Limit Circuit Open

TL;DR
Your Amana AMSS960803BN has overheated and the limit switch tripped. The most common fix is replacing a dirty air filter.
Disclaimer
This article is for informational purposes only and does not guarantee the accuracy or completeness of the information provided. Always turn off power and gas supply before attempting any repairs. If you smell gas, leave immediately and call your gas company. Consult a licensed HVAC technician for diagnosis and repair. Any actions taken based on this information are at your own risk.

What Does Code 4 Flashes Mean?

Status code 4 (four LED flashes) on the Amana AMSS960803BN indicates that the primary or auxiliary limit circuit is open. The furnace has overheated and the high-temperature safety switch (limit switch) has tripped to protect the heat exchanger. The circulator blower will continue running to cool the furnace down.

The limit switch is designed to shut off the gas burners when the temperature inside the furnace exceeds a safe level. This happens when there is not enough airflow over the heat exchanger to carry heat away. The blower fan keeps running to bring the temperature back down.

The most common cause is a dirty or clogged air filter that restricts airflow through the system. Other possible causes include blocked or restrictive ductwork, a faulty limit switch, or a failed circulator blower motor.

Common Causes

Cause Likelihood DIY?
Dirty or clogged air filter Most common ✓ DIY fix →
Blocked or restrictive ductwork Common ✗ Call a pro →
Faulty limit switch Uncommon ✗ Call a pro →

How to Fix It: Replace the Air Filter and Check Airflow

⚠ Safety First
Always turn off the furnace at the power switch or breaker and shut off the gas supply before beginning. Do not proceed if you smell gas — leave the area and call your gas company immediately.

What You'll Need

Steps

  1. Turn off electrical power at the breaker and shut off the gas supply valve Locate the furnace circuit breaker and flip it to OFF. Turn the gas shutoff valve to the OFF position (perpendicular to the pipe). If you smell gas, leave immediately and call your gas company.
  2. Locate and inspect the air filter Find the air filter — it is typically in a slot between the return air duct and the furnace blower compartment, or inside the blower compartment itself. Slide the filter out and hold it up to a light. If you cannot see light through it, it is too dirty and needs to be replaced.
  3. Replace the air filter Install a new filter of the correct size, making sure the airflow direction arrow on the filter frame points toward the furnace (away from the return duct). Slide it fully into the slot.
  4. Check all supply and return vents Walk through your home and make sure all supply vents and return air grilles are open and unobstructed. Move furniture, rugs, or other items that may be blocking airflow. Close no more than 20% of supply vents.
  5. Restore power and gas, then test Turn the gas supply valve to ON and flip the circuit breaker to ON. Allow the furnace to cool down for several minutes. Set your thermostat to call for heat and monitor the furnace through a complete heating cycle.
How to Verify
The furnace should complete a full heating cycle without code 4 reappearing. You should feel warm air coming from the supply vents. If the limit switch trips again with a clean filter and open vents, there may be a ductwork issue or a failing blower motor that requires professional diagnosis.

When to Call a Professional

Contact a licensed HVAC technician if:

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Sources

  1. Service Instructions - GMSS9*/GCSS9*/AMSS9*/ACSS9* Single Stage Gas Furnaces and Accessories

✓ Verified against manufacturer service manual — March 2026