Question when my furnace comes on it runs for 20 min or so I have to lower the thermostat manually, then when the house cools off I have to raise the thermostat. the furnace is 25 years old. I replace the thermostat but it still runs to long and when it does stop 5 sec later it starts again for about 4 sec. then it makes a bang and shuts down.Could you tell me what the problem could be, also the switch that you push on the furnace for a summer fan does nothing.
when it does stop 5 sec later it starts again for about 4 sec. then it makes a bang and shuts down.Could you tell me what the problem could be. What stops then restarts for 4 seconds ? the blower fan or the gas furnace? if your blower fan comes on /off your fan control may be bad.I do not know what type of fan/limit control you have, one type is a time delay the other ( found on older furnaces like yours) use a bimetal tube that senses the Heat exchanger air temperature and cycles the blower fan on/off. If you have that type it may be out of calibration ( 25 years old, nothing last forever ) I would consider replacing it.Buy on line. If it's your gas that comes back on and runs for 4 sec. you may have a wiring issue.I would remove wires from your t-stat R and W wire and jumper together let your heat run for 5 minutes then remove wires and see if your furnace shuts off and stays off. If it does then it's still something with your t-stat or the t-stat wires going to your furnace.You can bypass the t-stat and t-stat wire and jumper R to W to G at the furnace 24 volt low voltage terminal to check operation. pull the t-stat wires off and jumper at the furnace.proper way it should work, jumper r to w gas heat should start ( if you have the old style fan control ( bimetal type that senses the HX temp. ) your blower fan should start. then remove the jumper then gas should shut down and your blower fan will will stay running until the HX cools the the blower should shut down. The blower fan may or may not come on again once for a short time if there is still residual heat left in the HX. When was the last time your system was ever serviced?? You may want to consider having it checked. Have them check your gas pressure.at the gas valve .Have them check your fan control setting and basic operation, should only cost one hour of labor plus trip charge if no parts need to be replaced.
40+ years diversified experience.An HVAC/Refrigeration Self Employed Contractor since 1986. NATE Certifield. Answer questions pertaining to Residential and Commercial Air Conditioning , Warm Air Heating, Heat Pump systems.Mechanical and Electrical troubleshooting of these systems.Be as detailed as possible when describing problem.Packaged unit or split systems.No appliance questions.
Installation and Troubleshooting, Mechanical and Electrical, in following areas, Refrigeration ( Walk In and Reach In Coolers and Freezers ) Commercial Roof Top and Packaged Heating/Cooling ( Natural Gas,Propane, Electric, and Heat Pumps ) Computer Room Air Conditoning Systems,Commercial Residential Packaged and Split Systems Air Conditoning and Heat Pumps.Warm Air Oil , Natural and Propane Gas Heating systems.
Education/Credentials Graduated from Private Technical School in 1975. An HVAC/Refrigeration Contractor . Have Unlimited Heating/Piping and Cooling Contractor License.Limited Sheetmetal Contractors License.NATE Certifield. York Certifield Master Heat Pump Technician 1986. Served 33 years combination Active Duty Air Force ,
Air Force Reserves and Air National Guard in the HVAC/Refrigeration Shop/Mechanical Shop. Troubleshooting/Installing HVAC/Refrigeration Equiptment Worldwide. Retiring in 2003 as a Senior NCO ,and a Mechanical Superintendent.