A dirty coil is one of the most common — and most overlooked — causes of heating system performance problems. When dust, debris, and buildup accumulate on the evaporator or furnace coil, your HVAC system cannot move air properly. This restricted airflow leads to overheating, safety shut-offs, and uncomfortable temperature swings.
One of the biggest red flags of a dirty coil? Your high limit switch repeatedly popping. This is your furnace’s built‑in safety control responding to dangerous temperatures inside the system.
1. How a Dirty Coil Disrupts Heating Performance
The coil is responsible for heat transfer and proper airflow throughout your HVAC system. When it becomes coated with dust, pet hair, construction debris, or microbial buildup, airflow is restricted. Your furnace has to work much harder to move air across the coil, which puts stress on the blower motor and reduces overall heating efficiency.
A dirty coil can cause:
- Weak or uneven heat throughout the home
- Longer furnace run times
- Higher utility bills
- Excessive wear on HVAC components
2. Why a Dirty Coil Makes the High Limit Switch Pop
The high limit switch is a safety device that shuts down the furnace when temperatures inside the heat exchanger get too hot. This prevents overheating, fires, and damage to internal components.
When airflow is blocked by a dirty coil, heat cannot escape the furnace chamber efficiently. Temperatures rise quickly — and the high limit switch responds by shutting the system down to protect it.
Signs this is happening include:
- Furnace turning on and off rapidly (short cycling)
- Burning or hot metal smells
- Frequent system shutdowns or resets
- Furnace blowing cool air after overheating
3. Long-Term Risks of Ignoring a Dirty Coil
Allowing a coil to remain dirty doesn’t just reduce comfort — it can cause expensive and preventable damage.
Risks include:
- Blower motor burnout due to increased strain
- Cracked heat exchanger from repeated overheating
- Increased risk of furnace failure
- Higher dust and contaminant levels circulating through your home
4. How to Prevent High Limit Switch Trips and Heating Failures
The best way to prevent overheating and protect your furnace is to keep your coil clean.
Recommendations include:
Professional HVAC coil cleaning every 1–2 years
- Annual furnace tune‑ups to check airflow and safety controls
- Regularly changing HVAC filters (every 30–60 days)
- Ensuring ductwork is clean to support proper airflow
Trust Advanced Air Duct Cleaning
For over 60 years, Advanced Air Duct Cleaning has helped homeowners prevent heating failures, improve airflow, and protect their HVAC systems. Our NADCA‑certified technicians use specialized equipment to safely and thoroughly clean coils, ductwork, and blower assemblies — reducing the risk of high limit switch trips and keeping your home comfortable all winter long. Contact us today!