Life is busy and your furnace probably isn’t at the top of your list to think about. Until the cold weather hits, that is. You adjust your thermostat and expect the furnace to kick in. But what if it doesn’t? What now? It’s likely you’re experiencing any one of ten common furnace problems. Even if you’re able to make a quick fix for some, most problems will require a trained HVAC professional.


  1. Insufficient maintenance
  2. Dirty or clogged filters
  3. Normal wear and tear
  4. Electric ignition or pilot light issues
  5. Thermostat malfunction
  6. Furnace not heating at all
  7. Furnace not heating enough
  8. Furnace cycles frequently
  9. Blower runs continuously
  10. Furnace makes loud or unusual noises

Insufficient maintenance

Annual furnace maintenance and inspections by trained HVAC professionals can prevent unexpected problems and malfunctions. Repairs that could have been prevented with regular maintenance – such as a cracked heat exchanger – could be costly…

Dirty or clogged filters

Dirty filters make your furnace work harder, putting more strain on the unit. Clogged air filters restrict airflow, making it more difficult for your furnace to fully circulate the air. This reduced airflow may damage the limit switch that controls the fan. If that happens, you could be looking at higher energy costs. A furnace filter replacement is an easy fix.

Normal Wear and tear

Every furnace will experience wear and tear over time. Some signs could be airflow problems, slow response to temperature changes, issues with heat control, trouble staying at the set temperature, or high energy bills. Something like a slipped or frayed blower belt may be the culprit.

Electric ignition or pilot light issues

If you notice the heat is not circulating effectively, a faulty ignition or pilot light may be the problem. A defective ignition sensor, thermocouple problems (a device that measures temperature), a draft or clog in the appliance may result in an unlit pilot light. You’ll hear your furnace click, but it doesn’t fire up.

Thermostat malfunction

One of the most common furnace problems is a faulty thermostat. If your fan is constantly running, your thermostat may not be working.

Furnace not heating at all

Issues with your thermostat settings, power, gas, or the pilot light may be the reason. If your pilot light is weak, flickering, or yellow in color, it could be a sign of excess carbon monoxide in your gas furnace. Any change in your pilot light needs to be addressed immediately.

Furnace not heating enough

It could simply be a clogged filter. Or maybe your furnace is the wrong size for space. Of more concern is worn out ball bearings. If your furnace is making a scraping sound, immediately turn it off.

Furnace cycles frequently

Many things can cause frequent cycling. A clogged filter, improper airflow, a bad thermostat setting, or running your furnace too high or too low could be the cause. This will no doubt result in higher energy bills.

Blower runs continuously

If your blower is continuously running, the limit switch – the furnace component that activates and deactivates the blower assembly – is likely malfunctioning. It may be time to replace the limit switch.

The furnace makes loud or unusual noises

Loud sounds coming from your furnace, such as rumbling, squeaking, rattling, or popping are not normal. They may indicate mechanical problems, airflow reductions, a clogged burner, loose furnace panels that need to be tightened, or ductwork issues.


Schedule annual service calls

Schedule a trained HVAC professional to inspect your furnace once a year. The technician will make sure all components are functioning properly, and identify any additional services needed to ensure your furnace is safe to operate.

Regularly change the air filters

Dirty air filters can cause a wide range of problems. Follow the manufacturer’s directions for cleaning or replacement. In general, filters should be replaced every three months. However, during the winter season, it’s recommended that filters be changed every month.

Check your thermostat

If your furnace isn’t producing heat, first check the thermostat battery level. In some cases, just replacing the battery may fix the problem. Also, make sure the “Heat” mode is selected, then set your thermostat higher than room temperature to make sure the furnace kicks in.

If the blower on your furnace is continually running or your furnace is cycling too frequently, check your thermostat settings. Make sure your thermostat fan setting is on “Auto”. If the fan is set on “On”, the fan will run continuously.

Check your circuit breaker, fuses, and power

If your thermostat screen is blank and your furnace is not functioning, see if your circuit breaker tripped or if you blew a fuse. Make sure the power cord is plugged into an outlet.

Call an experienced HVAC professional

You can quickly and easily change your filters, check your thermostat battery, and confirm the circuit breaker, fuses and power are good to go. For everything else, however, you may need to schedule a furnace service repair if troubleshooting doesn’t resolve the issues.

First and foremost, it’s a safety issue. Unless you are trained in furnace repair, trying to repair mechanical problems or address combustion or gas-related issues could be extremely dangerous. You may also unintentionally void your warranty or cause more problems.

The bottom line, be proactive and take steps to prevent these problems from happening. If your furnace cannot be repaired or if it is cost-prohibitive to make the repairs, it may be time for a new furnace. Work with a trusted and reliable HVAC company that will ensure the new furnace is the right type and size for your home or business.

Whether you need a furnace repair or new installation, American AC Heat Plumbing is there for you backed by our 100% satisfaction guarantee. Call us today at 1-800-321-9494 or email us at to schedule an appointment.


James Smith

As you can tell from our humble beginnings in 1981, we began as a family-owned business and stayed a locally owned air conditioning and heating company in Los Angeles county for nearly 40 years.