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Problem: I am going through an ignitor almost every year. What could be the cause for my furnace cycling too much?

Problem: I am going through an ignitor almost every year. I think it is because my furnace cycles off and on too much. What could be the cause for my furnace cycling so much?

Answer: Below we have listed some reasons why your furnace ignitor might be going out so often. We hope this will help you from having to replace your ignitor so often!

*Please remember to turn off all electrical power to your HVAC system when trouble shooting or working on HVAC equipment. We most certainly do not want to see anyone get hurt or damage their equipment!

 If you need a furnace ignitor: Please Click Here to go to Our Furnace Ignitors Page If you have questions or would like for use to look up parts for your furnace, please email us anytime. Our email address is: For Bryant and Carrier equipment we will need product numbers. For Ruud and Rheem equipment we will need both the model number and serial numbers.

Below are listed some reasons that might cause your ignitor to go out prematurely:

  1. Handling the ignitor improperly by touching the gray glass part.
  2.  Installing an ignitor that is not made for the furnace.
  3.  High home line voltage. Check your voltage to see that you are in the 110 to 125 volt range. Anything over 125 volts is going to cause premature light bulb failure and furnace ignitor failure. Call your electric company if you are getting high voltage in your home. Your electric company should be able to place a transformer on your line to lower your line voltage.
  4. Debris from the heat exchanger or bugs/spiders can get on the ignitor while the furnace is not calling for heat and when there is a call for heat the debris/bug can short the ignitor out. It is a good idea to keep your furnace and heat exchanger clean so this does not happen.
  5. Moisture from a leaking air conditioner can cause water to drip down on the ignitor and electrical parts and ruin the parts. Please make sure your air conditioner’s condensate line stays open and your AC coil does not leak.
  6. The ignitors have just so many on off cycles in them. We have listed below some of the reasons why furnaces cycle off and on too much.

Below are listed some reasons why furnaces cycle off and on too much. It this cycling occurs it will cause premature part failure and can cause high heating bills.

1. Over-sized furnace. A furnace that is too large for you home cycles too much. If your furnace is sized properly on your coldest day the furnace should run almost continuously. Shutting off very few times. I went to an HVAC training meeting on energy conservation. The speaker said, “The inefficiency of a furnace is in the On, Off cycling.” He made this statement that on the coldest day your furnace should almost run continuously if sized properly.

2. A dirty filter or blower squirrel cage causes too much cycling. Your furnace will go off on high limit continuously because it is not getting enough airflow through the heat exchanger. The furnace goes off on high limit to keep from overheating the furnace and possibly causing a fire. This is why it is very important to keep those filters changed.

3. A dirty restricted air conditioning evaporator coil causes restricted airflow that causes too much cycling. Make sure your coil is not stopped up on the underneath side. I usually have to take off the coil end plates and use a vacuum cleaner and coil cleaner to get all the lint and dirt off. Make sure you clean in the direction the coil fins are running. If you do not, it will bend the fins over and cause more restrictions. A good tool to use is our air conditioner fin coil cleaning tool.

Please click here to go to our air conditioner fin comb tools page.

Please click here to see the AC evaporator coil cleaner that we sell.

4. Improper thermostat heat anticipator setting. Look at your gas valve and see the amp draw. Set you thermostat’s anticipator setting to this amp draw plus one amp more. If your gas valve says, “.4 amps” then set your thermostat to “.5″ amps. This will give you a little longer run time and a longer off time. If you have an electronic thermostat: Many of the electronic thermostats have temperature differential adjustments or like on the Honeywell thermostats have screws where you can adjust to make your furnace cycle a little longer.

Below we have a pictures on the left of a label off a White Rodger’s gas valve and on the right a Honeywell Round thermostat anticipator. The label shows that this White Rodgers gas valve model #38C03 Type 300 draws .23A or .23 amps. The anticipator shown in the picture on the right is set on .4 amps. If I were using this White Rodgers Gas Valve and the Honeywell Round thermostat I would set the anticipator one amp more than the gas valve draws, on .3 or a little past the.3. The little copper looking pointer can be moved to make your furnace stay on longer by using your finger to move the pointer. Again, you should look at your gas valve’s amp draw to determine your setting.

White Rodgers Gas Valve


6. Too much gas pressure causing the furnace to overheat because too much heat is being produced. This causes the furnace to cycle too much on high limit. Does your furnace’s gas pressure sound like a jet when it is running? Your gas pressure on your gas valve might be set too high. This produces too many BTU’s or too much heat. I would recommend a HVAC technician adjust this problem. Turning the adjustment screw clockwise gives more pressure. Counter clockwise gives less gas pressure. If you attempt to adjust this yourself, do not adjust more than 1/4 turn clockwise or counter clockwise. Delayed ignition, blow back,  and a mini explosion, could occur.  Again, I would recommend an HVAC technician do this adjustment. Getting this adjustment right will save you gas utility costs, and wear and tear on your furnace in the long run.

Valve with pressure screw cap removed

7. Your furnace flame sensor might need cleaning. If the furnace flame sensor needs cleaning or replacing the gas burners will not always stay on the first time. If the furnace is having flame sensing problems the furnace burners will light for 8 to 10 seconds then cut right back off. The cycle will start again and again. Usually the furnace will try to light 3 times then the furnace will go into lock out until the power switch on the furnace is reset.  This short cycling will cause the furnace and ignitor to cycle off and on too much. You can usually fix a flame sensor problem by cleaning the flame sensor with steel wool or light emery cloth sand paper. If you need a new flame sensor:  Please click here if you would like to see the furnace flame sensors we sell. If you have questions or would like for us to find out which flame sensor your furnace uses please email us anytime: Below we have a real good informative YouTube video made by Fix It Home Improvement Channel which explains ignitor and flame sensor operation and how to replace an ignitor and flame sensor. Thanks to Fix It Home Improvement Channel for making this informative video!

Below we have a Youtube video made by hvacrepairguy showing how to replace an ignitor. Thanks to hvacrepairguy for making this informative video.  If you have any other questions please feel free to email mail us: or comment in the comments section below.

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