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

What Does Code 4 Flashes Mean?

Four flashes on the Amana AMSS960803BN Integrated Control Module indicate that the primary or auxiliary limit circuit is open. The high-temperature limit switch has tripped because the air moving over the heat exchanger got too hot, and the board responds by shutting off the burners while keeping the circulator blower running continuously to carry the excess heat away.

The limit switch is a safety device that protects the heat exchanger from overheating. On this single-stage 96% furnace the burners fire at one fixed rate, so if airflow drops the heat exchanger temperature climbs quickly. Almost always the airflow restriction is the problem, not the heat itself. The most common cause is a dirty or clogged air filter; blocked or closed supply and return vents, restrictive ductwork, a slow blower, or an actual faulty limit switch are less common.

This code shares the limit-safety family with the six-flash rollout code, but they are not the same. Four flashes is a temperature-limit trip caused by restricted airflow, while six flashes is a flame-rollout trip caused by flames escaping the burner box — a far more serious condition. If you ever see six flashes instead of four, stop and treat it as the more urgent problem.

What You'll Notice

• The burners light and then shut off, but the blower fan keeps running non-stop
• Air from the supply vents feels cool or lukewarm while the blower continues to run
• The diagnostic LED flashes four times, pauses, and repeats
• The furnace short-cycles — it heats for a short time, trips off, then tries again

Common Causes

How This Is Diagnosed

The continuously running blower with the burners off is the tell-tale sign that a limit tripped rather than an ignition problem. Diagnosis starts at the cheapest, most common airflow restriction and works up: inspect and replace the air filter, then confirm supply registers and return grilles are open and unobstructed and no dampers are closed. If airflow is confirmed good and the code returns, a technician checks blower motor speed and performance and finally tests the primary and auxiliary limit switches for correct operation before replacing one.

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

What You'll Need

• Replacement air filter (correct size for your furnace) 🛒 Find at FiltersFast · 🛒 Find at Amazon
• Flashlight

Steps

1. Turn off power at the breaker and shut off the gas supply valve Switch the furnace circuit breaker to OFF and 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 — typically in a slot between the return duct and the blower compartment, or inside the blower compartment itself. Slide it 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 with the airflow arrow on the frame pointing 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 supply registers and return grilles are open and unobstructed. Move furniture, rugs, or other items blocking them, and avoid closing more than about 20% of your supply vents.
5. Restore gas and power, then test Turn the gas valve back to ON and switch the breaker on. Let the furnace cool for several minutes, then set the thermostat to call for heat and watch it through a full heating cycle.

When to Call a Professional

Contact a licensed HVAC technician if:

• The limit switch trips again after you replace the filter and open all vents
• The blower motor does not run, runs slowly, or makes unusual noises
• Airflow from the supply vents stays weak even with a clean filter
• The furnace overheats and trips on every heating cycle

✓ Verified against manufacturer service manual — March 2026