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AIR CONDITIONING & HEAT PUMP SYSTEMS
BACKDRAFTING HEATING EQUIPMENT
BACKUP HEAT for HEAT PUMPS
BANGING HEATING PIPES RADIATORS
BLOWER FAN OPERATION & TESTING
BOOKSTORE - InspectAPedia
BTU USAGE MONITORS
CARBON MONOXIDE - CO
CIRCULATOR PUMPS & RELAYS
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DIRECT VENTS / SIDE WALL VENTS
DRAFT REGULATORS, DAMPERS, BOOSTERS
DUCT SYSTEM & DUCT DEFECTS
ELECTRIC HEAT, DIAGNOSIS, REPAIR
ELECTRIC MOTOR DIAGNOSTIC GUIDE
FAN, AIR HANDLER BLOWER UNIT
FLOODED HEATING EQUIPMENT REPAIR
FLUE SIZE SPECIFICATIONS
GAS BURNER Flame & Noise Defects
GAS PIPING, VALVES, CONTROLS
GEOTHERMAL HEATING SYSTEMS
HEAT PUMPS, DIAGNOSIS, REPAIR
HEATING COST SAVINGS METHODS
HEATING OIL PIPING TROUBLES
HEATING OIL TANKS
HEATING SYSTEM NOISES
HEATING SYSTEM TYPES
LP & Natural Gas Safety Hazards
MANUALS & PARTS GUIDES - HVAC
MIXING / ANTI-SCALD VALVES
MOTOR OVERLOAD RESET SWITCH
NOISE, HEATING SYSTEMS
ODORS FROM HEATING SYSTEMS
OIL FILTERS on HEATING EQUIPMENT
OIL FILL PIPE LEAKS
OIL SPILL CLEANUP / PREVENTION
PLASTIC HEATER VENT
PUFFBACKS, OIL BURNER
RELIEF VALVE LEAKS
Reset Switch - Heater Primary Control
RESET SWITCH - ELECTRIC MOTOR
Reset Switch - Stack Relays
SAFETY, HEATING INSPECTION
SAFETY RECALLS CHIMNEYS VENTS HEATERS
SOLAR HEATING SYSTEM DESIGNS
SOOT on OIL FIRED HEATING EQUIPMENT
STEAM HEATING SYSTEMS
THERMOSTATS, HEATING / COOLING
VIDEO GUIDES: Heating System Videos
WINTERIZE A BUILDING
WOOD, COAL STOVES & FIREPLACES
WOOD STOVE SAFETY
Warm air heating furnace troubleshooting: how to diagnose & fix hot air furnace heating system problems. This article series answers most questions about hot air or warm air heating system troubleshooting, inspection, diagnosis, and repairs.
This article explains the diagnosis and correction of no heat conditions for warm air or hot air furnace and air duct heating systems. We describe how to inspect, troubleshoot and repair heating and air conditioning systems to inform home owners, buyers, and home inspectors of common heating system defects. We explain how to recognize and fix common heating system operating or safety defects and how to save money on home heating costs.
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This article explains how to diagnose and fix warm air or hot air furnace heating systems that are not working. Carson Dunlop Associates' sketch (left) shows the main layout of a basic warm air heating system.
[Click to enlarge any image]
If you don't know whether your heat is provided by a furnace (hot air) or boiler (hot water), or whether your fuel is oil, gas, or electric, and whether your heat is hot water, steam, or warm air, see HEATING SYSTEM TYPES.
If your heating system uses water or hydronic or hot water or radiator or baseboard hot water heating systems, instead of the article found here you should see HEATING LOSS DIAGNOSIS - BOILERS.
Note: some hybrid or mixed heating systems combine both hot water and hot air to heat a building, such as water to air systems which use a heating boiler (oil, gas, or electric) to heat water which circulates through (and inside of) a heat exchanger (that looks like a car radiator) - described at HEATING SYSTEM TYPES.
How to Diagnose Loss of Heat with a Warm Air or Furnace Heating System
Before turning to defects specific to a warm air furnace system, review our Oil / Gas Burner basic operating problems outlined at the top of HEATING LOSS DIAGNOSIS - BOILERS.
Details of Hot Air Heat Furnace Controls and Switches
Definition of Water to Air Heat Exchanger Heating Systems
Some heating systems combine both hot water and hot air to heat a building, such as water to air systems which use a heating boiler (oil, gas, or electric) to heat water which circulates through (and inside of) a heat exchanger (that looks like a car radiator).
For a detailed guide to inspecting, diagnosing, maintaining & repairing mixed, hybrid, water to air heating systems see FAN CONVECTOR HEATERS - HYDRONIC COILSDual hot water and warm air heating systems: as we explain at HEATING SYSTEM TYPES, some buildings are heated by a combination of separate hot water systems (circulating hot water through radiating devices like baseboards or radiators in some areas) and hot air systems (circulating warm air through ductwork into the occupied space in other areas).
These buildings will have both a hot air furnace and a completely separate hot water heating boiler installed. In this case these are completely separate heating systems and usually each serves different building areas.
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Frequently Asked Questions (FAQs)
Question: furnace burners don't ignite
Furnace fan powers up, ignitor coil heats up, but burners don't ignite. I have four (4) limit switches on the furnace. If I flick the switch on each one to reset them and restart the furnace, it works fine again for about half a day. However, when the furnace attempts to power up for a second cycle, the same thing happens again (burner don't ignite) unless I reset the switches again. Any help? (This is getting old and I'm not looking forward to the trip to the basement to reset the limit switches every 12 hours.)
Check the control wiring connections first; As you are describing a gas furnace, it sounds as if the gas valve is not opening.
Question: electric heating elements in our Lennox Elite Series 29 Furnace are not coming on
have a lennox elite series 29, blower comes on but heater doesnt and i have continuity on all four heating elements. any idea whats wrong - Mark 10.28/12
Search InspectAPedia for "Electric Backup Heat Repair, or go to Diagnose & Repair Electric Heat and you'll see our diagnostic procedure. The home page for that topic is at ELECTRIC HEAT, DIAGNOSIS, REPAIR.
I HAVE A LUXAIRE TWO VENT PIPE 90%afue downflow/horizontal gas furnace HI EFFICIENCY HEATER.The intake sucked in a leaf or leaves during the hurricane into the burner box, or they leaves are either stuck in the intake pipe or somehow is blocking the proper flow of vent air thru the system.My diagnosis view port is showing a 3 flash led pattern.The secondarary vent blower continues to run but will not allow system to start.Is their anyway to clear the debris and restart the system - Tom 10/29/12
For safety you need service by a trained technician.
Questions & answers or comments about how to fix a warm air heating furnace that is not working - how to diagnose the loss of heat in a building when the heat source is an oil or gas fired furnace.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.