Gas and Oil Home Heating Furnaces - indoor air circulating blower
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12-22-01, 12:47 PM
Hello, I have a Lennox gas forced air furnace which is about 30 yrs. old. It has a 1/6 h.p. direct drive circulating blower. The blower turns off after 5 min. of circulating heat. The flame is completely blue and heat comes out, but the blower gives out after five. I turn it off and wait awhile and then turn it back on and it does the same thing. What can be causing this? I was thinking that something overheats and then turns it off. Please let me know what to check for and where i could find the model number of my furnace and schematic for the parts? Thank you. :confused:
Sharp Advice
12-22-01, 01:45 PM
Hello DOA98 and Welcome to the Heating and Cooling Appliance forum and our Do-It-Yourself Web Site.
One of the most likely causes is a restricted intake air supply or warm air flow thru the ducting and or to and though the registers in the rooms. Check the filter. Replace or clean as needed. Open all warm air registers fully.
Could be a piece of furniture is too close to the intake air supply and restricting the intake. Could be a defective blower motor that spins too slowly or any of many other air flow problems.
The above conditions will still allow the fan to run but the restricted air flow causes the furnace to overheat which then activates the high limit safety switch which in turns cycles the burners off until the firebox cools down some.
Other possible and or probable causes:
Assuming the firebox {Heat Exchanger} isn't cracked and or the burner flames aren't smothering, etc.
Defective Glow Coil: {If equipped with one}
The glow coil may glow but just be too weak to allow current to continue to flow to the coils. The solenoid coils are also part of the electrical loop and may effect proper glow coil operation or functioning.
Defective Spark Igniton Module.
Defective Gas Valve Solenoid:
The gas valves solenoid is internal.
Take the entire gas valve unit to your local appliance parts store and have the entire assembly and parts tested.
Defective Gas Valve:
Remove entire unit as an assembly. Take the entire assembly to your local appliance parts store for testing. Gas valves are not repairable. Replacement is the only option if defective.
CAUTION: Do Not attempt to repair the gas valve! This is a non repairable item!
If the burners are cycling on and off, most likely it's cycling because the flame sensor element is dirty, defective or has a faulty connection.
Possible the fan ON switch is defective.
Could be the high limit switch is defective.
The fan motor itself could be overheating.
The fans squirrel cage bearings could be dragging and causing the fan motor to overheat. Try oiling the motor bearings and the squirrel cage bearings.
The bearings are located on the ends of the motor and the ends of the fan cage and may have oiling caps, which need to be lifted up. Add a few drops of any type of oil that is available.
FYI:
The do-it-yourself person can do electrical tests and continuity tests on several of the parts mentioned above. There are parts such as solenoids, gas valves, etc. when neither electrical tests and continuity tests will provide proof positive the part is actually functioning correctly. Therefore, do not rely solely on either test.
TIP:
The only positive proof any part is functioning correctly, is to carefully remove the part or parts you suspect to be the potential problems, and have the local appliance parts store personnel run the required tests.
Appliance parts dealers carry replacement parts for all appliances and are listed in the phone book under appliances. Electric motor repair shops can either fix, rebuild or replace the heaters existing motor. Shops also listed in the phone books.
Suggestions:
Read the manufacturers online web site for product information, problem solving methods, disassembly, reassembly methods, repair proceedures and instructions, pictorials and schematics, which may be available online.
Check the ARCHIVES, within this forum, for other postings on this topic and the replies offered.
Regards & Good Luck
Tom_Bart....TCB4U2B2B.....Company Enterprises
Fast.....Fair.....Friendly & Highly Efficient.....
Gas Appliances Forum Moderator
Energy Conservation Consultant & Natural Gas Appliance Problem Diagnostics Technician.
One of the most likely causes is a restricted intake air supply or warm air flow thru the ducting and or to and though the registers in the rooms. Check the filter. Replace or clean as needed. Open all warm air registers fully.
Could be a piece of furniture is too close to the intake air supply and restricting the intake. Could be a defective blower motor that spins too slowly or any of many other air flow problems.
The above conditions will still allow the fan to run but the restricted air flow causes the furnace to overheat which then activates the high limit safety switch which in turns cycles the burners off until the firebox cools down some.
Other possible and or probable causes:
Assuming the firebox {Heat Exchanger} isn't cracked and or the burner flames aren't smothering, etc.
Defective Glow Coil: {If equipped with one}
The glow coil may glow but just be too weak to allow current to continue to flow to the coils. The solenoid coils are also part of the electrical loop and may effect proper glow coil operation or functioning.
Defective Spark Igniton Module.
Defective Gas Valve Solenoid:
The gas valves solenoid is internal.
Take the entire gas valve unit to your local appliance parts store and have the entire assembly and parts tested.
Defective Gas Valve:
Remove entire unit as an assembly. Take the entire assembly to your local appliance parts store for testing. Gas valves are not repairable. Replacement is the only option if defective.
CAUTION: Do Not attempt to repair the gas valve! This is a non repairable item!
If the burners are cycling on and off, most likely it's cycling because the flame sensor element is dirty, defective or has a faulty connection.
Possible the fan ON switch is defective.
Could be the high limit switch is defective.
The fan motor itself could be overheating.
The fans squirrel cage bearings could be dragging and causing the fan motor to overheat. Try oiling the motor bearings and the squirrel cage bearings.
The bearings are located on the ends of the motor and the ends of the fan cage and may have oiling caps, which need to be lifted up. Add a few drops of any type of oil that is available.
FYI:
The do-it-yourself person can do electrical tests and continuity tests on several of the parts mentioned above. There are parts such as solenoids, gas valves, etc. when neither electrical tests and continuity tests will provide proof positive the part is actually functioning correctly. Therefore, do not rely solely on either test.
TIP:
The only positive proof any part is functioning correctly, is to carefully remove the part or parts you suspect to be the potential problems, and have the local appliance parts store personnel run the required tests.
Appliance parts dealers carry replacement parts for all appliances and are listed in the phone book under appliances. Electric motor repair shops can either fix, rebuild or replace the heaters existing motor. Shops also listed in the phone books.
Suggestions:
Read the manufacturers online web site for product information, problem solving methods, disassembly, reassembly methods, repair proceedures and instructions, pictorials and schematics, which may be available online.
Check the ARCHIVES, within this forum, for other postings on this topic and the replies offered.
Regards & Good Luck
Tom_Bart....TCB4U2B2B.....Company Enterprises
Fast.....Fair.....Friendly & Highly Efficient.....
Gas Appliances Forum Moderator
Energy Conservation Consultant & Natural Gas Appliance Problem Diagnostics Technician.