As the cooler weather of fall arrives and homeowners begin firing up their furnaces again (or switching their heat pumps over to heating mode), it’s not uncommon for a range of HVAC issues, big and small, to arise. 

With furnaces sitting for months unused and heat pumps spending months in cooling mode, the switchover to fall is a common time for problems to appear.

For HVAC pros making house calls, here’s a quick look at some of the most common issues you’ll face—plus some practical troubleshooting tips to consider. 

Faulty furnace ignitions 

If a furnace doesn’t ignite, the ignition system components like the igniter, flame sensor, or pilot light are the most immediate suspects. A weak flame signal, which can be read by measuring micro-amps (usually between 1.5 to 6 micro-amps), indicates a dirty or malfunctioning flame sensor. 

Troubleshooting tips: 

Always begin with a visual inspection. Follow the manufacturer’s user manual for recommendations. For example, if you find carbon build-up on the flame sensor, you might use fine-grit sandpaper to clean the rod gently. For igniters, measure the resistance; usually, a 40-90 ohms reading indicates a good silicon carbide igniter. 

Should the problem seem electrical, use a multimeter to check for 24V AC at the ignition control. If it’s missing, backtrack the circuit to find the issue. Remember, safety first – always turn off power before examining or touching electrical components.

Unreliable pilot lights 

Pilot lights that frequently go out can be frustrating. A weak or fluctuating flame often indicates an issue. It might be due to a draft blowing the pilot out, a malfunctioning thermocouple, or a problem with gas valve regulation.

Troubleshooting tips: 

First, examine the pilot flame. It should be steady and blue. If it’s yellow, there might be a draft or flue issue. For the thermocouple, ensure it’s appropriately positioned and test it with a multimeter. A suitable thermocouple should produce around 30 millivolts. 

If everything seems fine, yet the pilot doesn’t stay lit, the gas valve might be the culprit. Consult the manufacturer’s guide for more tips.

Frozen heat pump coils

The coils freezing over may indicate issues like low refrigerant levels or a dirty evaporator coil restricting airflow. When checking for refrigerant problems, look for signs of oil stains or listen for hissing noises, which might indicate leaks.

Troubleshooting tips: 

Start by checking the air filter and replace it if it’s dirty, as restricted airflow is a common cause of freezing coils. 

Use refrigerant gauges to check refrigerant levels are in line with the manufacturer’s recommendations. If they aren’t, you might be dealing with a leak. Use a bubble solution or electronic leak detector to try and find the source.  

Uneven heating throughout the home 

Uneven heating can stem from a range of issues. It might be due to obstructions in the ducts, malfunctioning dampers, or even an improperly sized furnace or ductwork system. A furnace that’s too big or small for a home can also lead to temperature imbalances. 

Troubleshooting tips: 

Use a thermo-anemometer to check the airflow velocity at each vent. If there are more than 20% differences between rooms, that’s usually a sign of blockages or leakages in the ductwork. 

To rule out issues with dampers, investigate each one to ensure they’re open and not stuck. 

If the home’s ducting seems airtight and the dampers are all functioning correctly, you can consider doing a Manual J load calculation to check if the HVAC system is sized perfectly for the home.

Wrapping up the transition to fall 

Homeowners rely on HVAC professionals to ensure their homes remain comfortable. This is especially important during transitionary times, for instance, as we shift from summer to fall.  

As we’ve highlighted, fall brings unique challenges, from furnaces that won’t ignite to heat pumps with frozen coils. But with the right troubleshooting strategies, most of these issues can be quickly and effectively addressed.