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My Thermostat is Working but my Heater is Not

My Thermostat is Working but my Heater is Not

One of the best parts about living in Los Angeles is how sunny and warm it is almost all year. Despite this, we still see some cold fronts down here. When the temperature starts to drop, there’s nothing better than coming home to nice cozy house.

What happens when you come home on a cold day, set the thermostat, and nothing happens? Your furnace doesn’t start? Here are a few reasons why you may find yourself asking, “why my thermostat is working but my heater is not?”

(Quick note: We normally refer to the furnace as the heater, but in this post, we will use heater and furnace interchangeably.)

The Furnace is On, but Not Heat is Coming Out

One of the best advancements we’ve made as a society are our safety protocols. Seatbelts have made driving safer, so have all the safety sensors in your car’s engine. Just like a car’s engine, your furnace is loaded with safety sensors.


While safety sensors are important and we’re happy they exist, they can also cause a lot of confusion among homeowners. There are a variety of seemingly small things that can trigger a safety switch. Once a safety switch is triggered, a certified HVAC technician is the only one who can reset the system.

Some of the issues that can trigger a safety sensor are:

  • A furnace that’s too hot
  • Carbon monoxide leak
  • Too much built-up pressure
  • Broken or leaking gas line

When a safety switch has gone off, your system will not work. You can change the settings all you want on the thermostat, but it won’t make a difference.

In this situation, it’s best to call an HVAC professional if your furnace isn’t creating any heat.

Gas Could be the Reason My Thermostat is Working but my Heater is Not.

A majority of all furnaces in the United States need three things to run properly: Gas, electricity, and water. Most homes are equipped with a line that pulls in natural gas from a city controlled supply.

Gas Could be the Reason My Thermostat is Working but my Heater is Not.

This gas is used for more than your furnace. Other appliances, such as the water heater, clothing dryer, and dishwasher also use natural gas.

Speaking of natural gas, a reason your thermostat is working, but the heater is not could be attributed to a stuck or broken gas valve or control board.

To test the gas line, you should start with the stove. For those with a gas powered stove, try to turn it on. If you can get a burner to ignite, your gas line is just fine. However, when the burners won’t turn on, you could have a major problem with your gas line.

The Furnace Needs Maintenance Work Done

At JW, we recommend two tune-ups per year for every Los Angeles home. An AC tune-up in the spring and a furnace tune-up in the fall.

While conducting a furnace tune-up, an HVAC expert from JW will inspect, clean, and test every part of your furnace. They’ll make sure everything works as it should and is ready for the season ahead.

The HVAC tech will also let you know if there are any potential fixes on the horizon. As we like to say, take care of small problems before they become big, expensive issues.

When was the Last Time You Changed Your Air Filter?

This is the question we wish we could ask every homeowner. Unfortuantely, we just can’t. But this is something you can usually take care of on your own.

Air filters play an important role in your HVAC system, and they need to be regularly checked and changed. No matter what type of air filter you have, they all need to be cleaned or replaced.

A dirty air filter may be the Reason My Thermostat is Working but my Heater is Not.

Over time and with use, all air filters get full. It’s a sign they’re doing their job correctly. An air filter has two important jobs. First, they keep dust and other debris from settling within the HVAC system. And second, they trap indoor air contaminants from getting into your temperature treated air.

Due to the nature of its job, you can see why an air filter would get full or clogged. When an air filter is clogged, air can’t freely move through it. This means your furnace is working extra hard to produce enough air that’ll make it through the full filter.

When an air filter is too full, your thermostat will continue to work, but your heater will not.

Is Your Furnace Short Cycling?

All furnaces run on a cycle. The cycle consists of pulling in air from the home, heat treating said air, then distributing the air throughout the home until the ambient temperature is matching what’s programmed into the thermostat.

A cycle usually lasts between 15 and 20 minutes. The heating cycles only happens when the home needs warm air. Despite this, there can be a lot of issues with short cycling.

Short cycling happens when the furnace can’t produce enough air for the home, or when the furnace produces too much air for the home. Some other reasons your furnace will short cycle are if:

  1. The furnace itself is overheating
  2. The air filter is too dirty and too full of debris
  3. Your flame sensor isn’t working
  4. The thermostat is in the wrong spot
  5. Your Furnace is too big for your home

JW provides top notch service for our communities in Los Angeles County. To schedule an appointment, call the number at the top of the screen or click here to book online.