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Imagine being out in the cold, and then coming home to a chilly house. Finding out that the furnace is not working is the last thing any homeowner would like to discover after being out and about and tired after a day’s work. Nothing could be more frustrating than knowing that the furnace is not turning on and it is not warming up the whole house.

Fortunately, help is within reach. There are certified local HVAC professionals who are more than happy to help out. But before ringing them in, it is best to find out the root cause, and check if it is something that could be easily resolved. There are several reasons why a furnace would not suddenly turn on, and knowing these possible causes could help a homeowner save time and effort in terms of dealing with the issue. If it is easy like just turning on a switch or checking the thermostat, then at least the homeowner can already resolve it from his end. However, if it is something complicated, then the homeowner can just easily decide to call in a licensed HVAC technician who can immediately diagnose and resolve the issue.

How a furnace works

Knowing the basics of how a furnace works would at least shed light on why it would suddenly stop working or would not turn on at all. The furnace usually starts doing its job once the thermostat detects that the indoor temperature is below the desired temperature of the homeowner.

The thermostat will then send a signal to the circuit control board to start the whole heating cycle. This will then trigger the gas valve to open up and the ignition to turn on. The flame produced will then heat the air that the fan will blow through the whole house, via the various ducts and air vents. The flue gasses then pass through the heat exchanger and get out of the house through the flue pipe.

Why the furnace won’t turn on

There are several possible reasons why a furnace would not turn on. This article will round up these possible causes so that it will be easier for the homeowner to deal with these situations:

The furnace would not turn on because the switch is off

It is possible that the furnace switch was accidentally turned off by any of the household members. For instance, while doing a whole house cleaning or decluttering, someone may have accidentally flicked the switch. It is also not impossible that a handyman, an electrician, or a plumber turned it off while working on the house. Check this area first before calling in the pros.

The breaker tripped causing the furnace to not turn on

When the breaker connected to the furnace gets tripped, the furnace will not turn on. Since the breaker will stop the power supply to the circuit that serves the furnace, the heater will not work at all. If the furnace does not turn on, yet the switch is on, check the breaker panel and see if one of the switches has been tripped. If it is tripped, then flip it back to restore power to the furnace.

Failing thermostat

It is also possible that a failing thermostat is causing the furnace to stop working. The thermostat is the key device that signals all other mechanisms within the furnace to start the heating cycle. If it is set to cool, or it has run out of batteries then the furnace will not work correctly. Regularly check the batteries and replace them as needed to avoid unnecessary inconveniences and discomfort.

Wrong thermostat setting

If the thermostat is set incorrectly, it will fail to trigger the control board to start the whole heating process. Take a look if the thermostat is in the HEAT setting to ensure that the furnace will work as soon as the indoor temperature drops below the set temperature. Sometimes, the thermostat is left in the COOL mode hence it does not work even if it should have already started working.

Another thermostat setting worthy of looking into is the FAN setting. The FAN should be in AUTO mode instead of fan only so that once the temperature drops and the furnace starts working, the fan could blow heated air throughout the house. 

Likewise, inspect the temperature level. Sometimes it has not to be adjusted to the desired temperature, hence the house seems cooler than expected. If it is set way too low then it will be a lot colder. Consider purchasing a SMART or Programmable thermostat so that adjustments can be automatically done to ensure overall comfort throughout the house.

Loose or worn-out thermostat wiring

Sometimes, the wiring of the thermostat gets damaged or worn out hence it could no longer function correctly. The best thing to do is to check the thermostat if the wirings are still correctly in place. Just remove the plate cover, and observe if the wirings remain secure and that there is no visible damage to any of the wirings.

The gas valve is in off position so no gas to heat exchanger

Inspect the gas valve if it is turned on. It is turned on when the valve’s handle is parallel with that of the fuel or gas line. However, if the gas valve’s handle is perpendicular to the gas line, it means that the gas valve is turned off. Without a gas supply, the furnace will not work. Turn the handle on, and check if the furnace will start doing its job.

A worn-out capacitor can cause the furnace to fail

Another likely culprit when the furnace fails to turn on is a bad capacitor. The capacitor is a crucial part of the furnace’s mechanism that nudges the furnace’s motor to start and keep running. But like any mechanism, it could wear out over time hence it is best to check it from time to time. A licensed HVAC electrician can easily test and detect a failure in an HVAC capacitor. In case it is worn out, then a replacement is in order.

The furnace would not turn on because the blower motor is filthy or burned out

Another reason why a furnace would suddenly not turn on is when the blower motor is worn out or very filthy. Without a working blower motor, the furnace cannot pull cold air from the house, heat it back in, and redistribute it throughout the various ducts within the home.

Like any mechanical part of a furnace, the blower motor is bound to accumulate dirt and debris. Without regular and proper maintenance, it will get filthy. Over time it will wear out as well. The build-up of dirt will hinder proper airflow, restricting both the inflow and outflow of air. When this happens the furnace could overheat and consequently shut down. Once this occurs, the furnace will stop working.

Apart from potentially causing a furnace shutdown, a filthy blower motor also decreases the heating efficiency of the furnace. Since the airflow is not enough, the furnace will work double time to produce heated air and consume more energy than needed. This in turn will cause upward spikes in the electricity bill. A certified HVAC technician can easily spot a worn-out blower so it is best to seek HVAC servicing if this seems to be the case.

A dirty air filter is causing furnace failure

Filters blocked with built-up dust and debris are another possible culprit when it comes to a furnace failure. Restricted airflow weighs down the furnace’s operations, causing it to overheat and eventually shut down.

Furnace manufacturers recommend that filters are replaced every three months or even shorter especially when there are household members with allergies or if household pets are roaming around the house. The debris, dust, dander, and pollen clog the filters and restrict normal airflow that allows the furnace to take in the process, and redistribute warm air throughout the house. Check the filters, and change them if needed.

Defective flame sensor

Sometimes, the flame sensor no longer functions correctly, hence the furnace’s safety mechanism gets activated and shuts down. The flame sensor is a safety feature that detects if there is a flame so that the gas valve could be opened. If the flame sensor is worn-out or dirty, it will malfunction and prevent the ignition process from taking place. So even if everything seems fine in terms of mechanism, the flame sensor prevents ignition as its sensor is already filled with dust, debris, carbon deposits, and combustion soot. Have a licensed HVAC technician take a look at the flame sensor and clean or replace if necessary.

The safety float switch is activated

Every furnace has a safety float switch that disables the furnace operations when the condensate drain pan gets filled with excess water. The safety feature is meant to prevent water damage at home. While removing the water from the drain pan is a quick fix, the issue is bound to recur since an overfilled drain pan is an indication of a clogged drain line. The long-term solution to this issue is to have a certified furnace technician come over to carry out a permanent fix to the problem.

Find out why water could be dripping from your vents.

Malfunctioning door switch

If the door switch is worn out, the furnace will not work even if its mechanism is perfectly fine. As one of the safety features of the furnace, it will not turn on if the furnace door switch is unhinged or slightly open. Check the furnace’s front panel to see if the door is ajar and if the switch is malfunctioning, because if it is it needs replacement. It is also best to inspect whether there are loose screws or tampered parts that cause the cabinet door to remain unhinged.

The high limit switch is turned off

The high limit switch may have been triggered, hence the furnace is not turning on. The high-limit switch is yet another safety feature of the furnace that automatically shuts it down once it detects that the furnace is overheating. If the high limit switch fails, it will not be able to monitor and trigger the blower motor to start working. If the high limit switch is dirty, it will fail to sense the temperature inside the furnace, and consequently, fail to signal the blower motor to start working. It is also possible that it got worn out over time, so it is best to have it replaced. An HVAC professional can easily diagnose this issue and replace the damaged switch.

The pressure switch is triggered for safety

Another cause of furnace failure is a triggered pressure switch. The pressure switch is the safety mechanism that ensures that the flue gasses produced by the furnace are exhausted correctly outside the home. Without this feature, the whole household is at risk for gas poisoning or getting sick due to inhalation of exhaust fumes. Once this device notices a negative static pressure in the draft inducer motor or the flue pipe, it will get triggered and will shut the furnace down.

If this particular safety device is worn out, damaged, or dirty, it could malfunction or get triggered incorrectly. Routine professional maintenance is key to ensuring that the pressure switch and other safety devices are working optimally.  Learn how to Reset a furance using the heater reset button here.

Worn-out flame roller switch

It is possible that flame could get out of the combustion chamber and cause immediate danger to everyone in the household. Rolling flames pose a severe fire hazard in any home, and the flame roller switch prevents this from occurring.  The switch in essence turns off the heating system once it overheats to prevent furnace fires. If the rollout switch is malfunctioning or damaged, then it could override furnace operations incorrectly.

How to avoid heating and furnace problems

The best way to avoid furnace and heating issues during winter is to have annual maintenance during the fall season. By ensuring that the furnace system is in A1 condition, there are fewer chances for it to bog down when it is cold outside. A professional HVAC company like us at Reliable Standard Heating and Air will be more than happy to help you keep your furnace working in top condition.

The routine, professional furnace tune-ups that we offer are meant to keep your furnace in an optimal state. Likewise, it will help you raise the level of energy and heating efficiency since the whole system is working at its best. Surely, you will get your money’s worth as you try to 

Is your furnace not turning on?

 If your furnace is not turning on, get the pros to look into it. Here is what you can check first if your heater isn’t working. Or Call us up at Reliable Standard Heating and Air, or schedule a furnace check through our convenient online scheduling system and we will surely be in your place at your preferred date and time. Get in touch with us today! Servicing Rancho Bernardo, Carmel Valley, Escondido, Del Mar, Poway, San Marcos, Vista, and La Jolla.

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