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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 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
GAS 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 Plexvent / Ultravent RECALL
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
ZONE VALVES, HEATING
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.
Green link shows where you are in this article series.
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
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.
Question: Kerr furnace keeps going off on reset
Hello my friend (a newly graduated hvac technician) and I have been trying to help a local woman with heating troubles. She has a 'Kerr' Oil Fired Warm Air Furnace. We have tried on several occasions to help by troubleshooting in order to make it/ keep it functional. It seems to work for a heat cycle or two and even though it starts, each time the system has needed to be reset. The things that have been done so far include cad cell tested and cleaned, air flow adjusted, tested/ adjusted limit settings and changed over to new thermostat. Can you direct us as to what could be the source of the problem? We really can not afford to hire a technician...and would sincerely appreciate any assistance you can provide. - M.D. 12/28/2013
A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone. You will find additional depth and detail in articles at our website. That said I offer these comments: Hi Mary, I'd like to help diagnose the Kerr furnace you discuss, but with so little information I'm not confident about what specific details I can recommend by email. I'll make a few suggestions, then you may be able to tell me more and I may be able to comment further.
While there is nothing harmful in the steps you've taken so far, they sound a bit random to me. I'm doubtful, for example, that changing a thermostat would have much to do with a furnace going off on reset - except for a very odd case of a furnace that kept switching the call for heat on and off very rapidly.
And your cleaning the cad cell is a fine idea, but doesn't consider that if the cad sell was dirty then the flame is probably running smoky and there is an adjustment or fuel or nozzle problem, nor does it consider the possibility of a bad cad cell that needs replacement.
When a heating system keeps going off on reset usually there is a problem with fuel or combustion: dirty oil filter, defective fuel unit, air in oil lines, cracked or improperly set electrodes etc. You can take a look at two diagnostic pathways at InspectApedia, one for furnaces and the second focused on oil burners. See
where we include diagnostic flowcharts and very thorough debugging steps.
You should also have at hand the installation and set-up instructions for the Kerr oil fired furnace you mention - though you didn't give me a model and serial.
Kerr oil furnaces are produced by Granby Industries, of which Kerr Energy Systems produces both forced warm air heating furnaces and heating boilers. Contact information: http://www.granbyindustries.com - for furnaces is Granby Furances Inc., 12118 Hwy 209, PO Box 637 Parrsboro NS B0M 1S0 Phone: 902-254-2543 Fax: 902-254-3863 gfisales@GranbyIndustries.com
I would contact the company with the furnace model and serial number to obtain installation instructions if you don't already have them. There are several Kerr furnace models: Gemini, Eclipse, Compact, Paradigm (High efficiency), Summit, Scotty, & Scotsman - so you can see that you'll need your model and serial number to obtain the right installation and maintenance instructions.
But most often a problem with an oil fired furnace that keeps going off on reset will be traced to a fuel, electrode, cleaning, or adjustment problem that is more generic to oil burners rather than to the specific furnace model.
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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