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HEATING SYSTEMS

AFUE DEFINITION, RATINGS
AGE of AIR CONDITIONERS & HEAT PUMPS
AGE of HEATERS, BOILERS, FURNACES
AIR CONDITIONING & HEAT PUMP SYSTEMS
AIR FILTERS for HVAC SYSTEMS
AIR HANDLER / BLOWER UNITS
AIRBOUND HEAT SYSTEM REPAIRS
ANODES & DIP TUBES on WATER HEATERS
ANTIFREEZE for BOILERS
ANTI SCALD VALVES
APPLIANCE EFFICIENCY RATINGS
ASBESTOS IDENTIFICATION IN buildings

BACKDRAFTING HEATING EQUIPMENT
BACKFLOW PREVENTERS, HEAT
BACKDRAFTING HEATING EQUIPMENT
BACKUP HEAT for HEAT PUMPS
BAROMETRIC DAMPERS
BASEBOARD HEAT
BIOGAS PRODUCTION & USE
BLEVE EXPLOSIONS
BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BLUE vs YELLOW COMBUSTION FLAMES
BLUERAY Recall
BOILERS, HEATING
BOILER PRESSURE & TEMPERATURE SETTINGS
BOOKSTORE - InspectAPedia
BTU USAGE MONITORS
BUILDING SAFETY HAZARDS GUIDE

CAPACITORS for HARD STARTING MOTORS
CARBON DIOXIDE - CO2
CARBON MONOXIDE - CO
CHEMICAL TREATMENTS for BOILERS
CHIMNEY INSPECTION DIAGNOSIS REPAIR
CHIMNEYS & Flues - Asbestos Transite Pipe
CHINESE DRYWALL HAZARDS
CIRCULATOR PUMPS & RELAYS
COOL OFF HEAT, Thermostat Switch
COMBUSTION AIR
COMBUSTION AIR for TIGHT buildings
COMBUSTION GASES & PARTICLE HAZARDS
COMBUSTION PRODUCTS & IAQ
COMPLETE COMBUSTION, Stoichiometric
CREOSOTE FIRE HAZARDS
Curved Brick Chimneys - Sulphation
CONDENSING BOILERS/FURNACES
CONDENSING BOILERS/FURNACES DAMAGE
CONVECTOR HEATERS - HYDRONIC COILS

DEFINITION of Heating & Cooling Terms
DIAGNOSE & FIX AIR CONDITIONER / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DIRECT VENTS / SIDE WALL VENTS
DIRECTORY of OIL TANK EXPERTS
DRAFT HOODS - gas fired
DRAFT MEASUREMENT, CHIMNEYS & FLUES
DRAFT REGULATORS, DAMPERS, BOOSTERS
DUCT SYSTEM & DUCT DEFECTS
DUST, HVAC CONTAMINATION STUDY
DUST SAMPLING PROCEDURE

ELECTRIC HEAT, DIAGNOSIS, REPAIR
ELECTRIC MOTOR DIAGNOSTIC GUIDE
ELECTRIC MOTOR OVERLOAD RESET SWITCH
ELECTRICAL POWER SWITCH FOR HEAT
EVAPORATIVE COOLING SYSTEMS

FAN, AIR HANDLER BLOWER UNIT
FAN AUTO ON Thermostat Switch
FAN, COMPRESSOR/CONDENSER UNIT
FAN CONVECTOR HEATERS - HYDRONIC COILS
FAN LIMIT SWITCH
FAN NOISES
FILTERS, AIR for HVAC SYSTEMS
FILTERS, OIL on HEATING EQUIPMENT
FIRE SAFETY CONTROLS
FIREPLACES & HEARTHS
FLAME COLOR, BLUE vs YELLOW COMBUSTION
FLOODED HEATING EQUIPMENT REPAIR
FLOODED WATER HEATER REPAIR
FLUE SIZE SPECIFICATIONS
FLUE VENT CONNECTORS
FREEZE-PROOF A BUILDING
FUEL OIL TYPES & CHARACTERISTICS
FUEL UNIT, HEATING OIL PUMPS
FURNACES, HEATING

GALVANIC SCALE & METAL CORROSION
GAS BURNER Flame & Noise Defects
GAS FIRED WATER HEATERS
GAS PIPING, VALVES, CONTROLS
GAUGES ON HEATING EQUIPMENT
GEOTHERMAL HEATING SYSTEMS

HEAT EXCHANGER LEAK TEST
HEAT LOSS in BUILDINGS
HEAT LOSS DETECTION TOOLS
HEAT LOSS INDICATORS
HEAT LOSS PREVENTION PRIORITIES
HEAT LOSS R U & K VALUE CALCULATION
HEAT PUMPS, DIAGNOSIS, REPAIR
HEAT TAPES & CABLES on Roofs for Ice Dams
HEATING COST FUEL & BTU Cost Table
HEATING COST SAVINGS METHODS
HEATING LOSS DIAGNOSIS-BOILERS
HEATING LOSS DIAGNOSIS-FURNACES
HEATING OIL CLOUD WAX GEL POINT
HEATING OIL EXPOSURE HAZARDS, LIMITS
HEATING OIL - OLD, USEABLE?
HEATING OIL PIPING TROUBLES
HEATING OIL SHELF LIFE
HEATING OIL SLUDGE
HEATING OIL USAGE RATE
HEATING SMALL LOADS
HEATING SYSTEM INSPECT DIAGNOSE REPAIR
HEATING SYSTEM INSPECTION DETAILS
HEATING SYSTEM NOISES
HEATING SYSTEM TYPES
HIGH EFFICIENCY BOILERS/FURNACES
HOT WATER HEATERS
HOT WATER IMPROVEMENT

INSULATION INSPECTION & IMPROVEMENT

LOW VOLTAGE BUILDING WIRING
LOW VOLTAGE TRANSFORMER TEST
LP & Natural Gas Safety Hazards

MANUALS & PARTS GUIDES - HVAC
MIXING / ANTI-SCALD VALVES
MOTOR OVERLOAD RESET SWITCH

Natural Gas Combustion Products
NO HEAT - BOILER
NO HEAT - FURNACE
NOISE / SOUND DIAGNOSIS & CURE
NOISE AIR CONDITIONER / HEAT PUMP
NOISE, DUCT VIBRATION DAMPENERS
NOISE, HEATING SYSTEMS
NOISE, PLUMBING
NOISE, WATER HEATER

ODORS FROM HEATING SYSTEMS
OIL BURNERS
OIL BURNER FUEL UNIT
OIL BURNER INSPECTION & REPAIR
OIL BURNER NOISE SMOKE ODORS
OIL BURNER NOZZLE & ELECTRODES
OIL BURNERS, RETENTION HEAD
OIL BURNER SOOT & PUFFBACKS
OIL FILTERS on HEATING EQUIPMENT
OIL FILTER MISSING
OIL FUEL TYPES & CHARACTERISTICS
OIL HEAT FIRE SAFETY CONTROLS
OIL LINE CLOGGING FIX
OIL LINE QUICK STOP VALVES
OIL LINE SAFETY VALVES
OIL ODORS, LEAKY OIL TANK PIPING
OIL PUMP FUEL UNIT
OIL SPILL CLEANUP / PREVENTION
OIL TANKS

PLASTIC HEATER VENT
PULSE COMBUSTION HEATERS
PASCAL CALCULATIONS
PRESSURE REDUCING VALVES
PRESSURE REGULATOR, WATER
PUFFBACKS, OIL BURNER
PUMPS, PONY PUMPS

RADIANT BARRIERS
RADIANT HEAT
RADIANT HEAT Floor Mistakes to Avoid
RADIANT HEAT TEMPERATURES
RADIANT SLAB FLOORING CHOICES
RADIANT SLAB TUBING & FLUID CHOICES
RADIATORS
REFRIGERANTS & PIPING
RELIEF VALVE LEAKS
RELIEF VALVES - TP Valves on Boilers
RELIEF VALVES - STEAM TP VALVES
RELIEF VALVES - Water Heaters
RELIEF VALVES - Water Tanks
Reset Switch - Heater Primary Control
Reset Switch Broken - Quick Repair
RESET SWITCH - ELECTRIC MOTOR
Reset Switch - Stack Relays

SAFETY HAZARDS & INSPECTIONS
SAFETY HAZARDS GUIDE
SAFETY, HEATING INSPECTION
SAFETY RECALLS, Chimneys, Vents, Heaters
SOLAR HEATING SYSTEM DESIGNS
SOLAR HOT WATER HEATERS
SOOT on OIL FIRED HEATING EQUIPMENT
SPILL SWITCHES - Flue Gas Detection
SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS
STACK RELAY SWITCHES
STAIN DIAGNOSIS on BUILDING INTERIORS
STEAM HEATING SYSTEMS

TANKLESS COILS
Thermal Expansion Cracking of Brick
THERMAL EXPANSION of HOT WATER
THERMAL EXPANSION of MATERIALS
THERMAL IMAGING, THERMOGRAPHY
THERMAL IMAGING MOLD SCANS
THERMAL MASS in BUILDINGS
THERMAL TRACKING & HEAT LOSS
THERMOSTATS, HEATING / COOLING
Transite Pipe Chimneys & FlueS

VIDEO GUIDES: Heating System Videos
VIDEO GUIDES - InspectAPedia.com

WATER HEATERS
WATER HEATER SAFETY
WATER HEATERS for HOME HEATING USE?
WATER HEATER NOISES
WATER HEATER SCALE - De-Liming Procedure
WATER HEATER SCALE PREVENTION
WINTERIZE A BUILDING
WOOD, COAL STOVES & FIREPLACES
WOOD STOVE SAFETY

ZONE DAMPERS
ZONE VALVES

More Information

Photograph of a burning-up and possibly dangerous oil-fired heating boilerHow to Recognize & Diagnose Heating Boiler Problems
     

  • How to diagnose loss of heat or no heat when your building is heated by a hot water boiler (a hydronic heating system)
    • Types of Boiler Defects
    • Air-bound radiators or piping
    • Diagnose Loss of Heat
    • Diagnose Oil Heat Noises
    • Evaluate Heating Boiler Leaks
    • Combustion Air Defects
    • Heat Won't Turn Off - Stop Unwanted Heat
    • Heating Malfunctions & Implications
    • Heating Defects & Implications
  • DIAGNOSE & FIX HEATING PROBLEMS-BOILER - separate article
  • Questions & Answers about diagnosing problems with residential hot water heating systems: the heating boiler
  • References

Click to Show or Hide Related Topics

  • BOILERS, HEATING - home
  • AIR BLEEDER Valves
  • AIR SCOOPS PURGERS SEPARATORS
  • AIRBOUND HEAT SYSTEM REPAIRS
  • ANTIFREEZE for BOILERS
  • AQUASTAT CONTROL Functions
  • BAROMETRIC DAMPERS
  • BOILER CONTROLS & SWITCHES
  • BOILER INSPECTION GUIDE
  • BOILER LEAKS CORROSION STAINS
  • BOILER LEAKS, HOW TO LOCATE
  • BOILER NOISE SMOKE ODORS
  • BOILER OPERATING PROBLEMS
  • BOILER OPERATION DETAILS
  • BOILER PRESSURE & TEMPERATURE SETTINGS
  • BOILER PRESSURE CONTROLS & SETTINGS
  • CAD CELL RELAY SWITCH
  • CHECK VALVES, HEATING SYSTEM
  • CHEMICAL TREATMENTS, Boiler
  • CIRCULATOR PUMPS & RELAYS
  • COMBUSTION AIR
  • CONDENSING BOILERS/FURNACES
  • CONVECTOR HEATERS - HYDRONIC COILS
  • DIAGNOSE & FIX HEATING PROBLEMS-BOILER
  • DRAFT REGULATORS, DAMPERS, BOOSTERS
  • ELECTRIC MOTOR DIAGNOSTIC GUIDE
  • ELECTRICAL POWER SWITCH FOR HEAT
  • EXPANSION TANKS
  • FILTERS, OIL on HEATING EQUIPMENT
  • FIRE SAFETY CONTROLS
  • FUEL UNIT, HEATING OIL PUMPS
  • GAS BURNER Flame & Noise Defects
  • GAS FIRED HEATING BOILER PROBLEMS
  • GAS FIRED WATER HEATERS
  • GAUGES ON HEATING EQUIPMENT
  • HEATING COST SAVINGS METHODS
  • HIGH EFFICIENCY BOILERS/FURNACES
  • LIMIT SWITCHES, BOILERS
  • LOW WATER CUTOFF VALVES, BOILERS
  • MIXING / ANTI-SCALD VALVES
  • NOISE, HEATING SYSTEMS
  • OIL BURNERS
  • OIL LINE QUICK STOP
  • OIL LINE SAFETY VALVES
  • PRESSURE GAUGE, BOILER
  • PRESSURE & TEMPERATURE SETTINGS
  • RELIEF VALVES - TP VALVES
  • RESET SWITCH - Primary Control
  • RESET SWITCH - electric motor
  • SPILL SWITCHES
  • STACK RELAYS
  • STEAM HEATING SYSTEMS
  • THERMOSTATS, HEATING / COOLING
  • WATER FEEDER VALVES, HYDRONIC BOILER
  • ZONE VALVES
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Heating boiler defects: Here we explain how to recognize & diagnose problems with residential heating boilers, including loss of heat, heating boiler noises, leaks, odors, or smoke, and high heating costs. This website answers most questions about central hot water heating system troubleshooting, inspection, diagnosis, and repairs. Also see OIL BURNERS or GAS BURNER Flame & Noise Defects depending on the fuel your boiler uses.

Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.

How To Recognize Heating System Defects: the Heating System Inspector Must Know the Equipment

If you have no heat and need help diagnosing the cause, see HEATING LOSS DIAGNOSIS-BOILERS or HEATING LOSS DIAGNOSIS-FURNACES. The photograph at page top shows a heating boiler which is burning through it's steel outer jacket - this condition is a potential fire hazard and requires immediate inspection and repair. There is probably a combustion gas leak at this heater. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

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, it will be helpful to first review our descriptions of hot water or "hydronic" heating systems at BOILER COMPONENTS & PARTS and BOILER OPERATION DETAILS which describe hot water heating systems, and also review our descriptions of furnaces and hot air heat at FURNACES, HEATING COMPONENTS

Types of Defects and Problems with Hot Water Heating Boilers - Hydronic Heating Systems, Loss of Heat, Noises, Leaks

What sort of defects should you look for when inspecting a heating system?

  • Unsafe conditions on the heating system such as signs of burn-out of the combustion chamber liner, unsafe relief valves, unsafe flue gas venting, fuel leaks, combustion gas leaks. Burn marks on boilers or furnaces, evidence of leaky or stuck pressure relief valves, evidence of tampering with the safety controls, abnormal heater control settings, evidence of chimney, flue, or flue gas venting defects, are all safety concerns.
  • Loss of heat - boiler or furnace won't operate, or system operates but heat is not produced in the living area - we provide a guide to diagnosing the reasons for "no heat" beginning at NO HEAT - BOILER / FURNACE DIAGNOSIS. If your hot water heating system is running (the steam or hot water boiler is making noise and seems to get hot) but some of your radiators or baseboards are cold, see RADIATORS and AIRBOUND HEAT SYSTEM REPAIRS.
  • Improper Heating System Function: noises, odors, soot, burn marks on the furnace or boiler, unreliability, inadequate heat distribution. Soot production by gas fired heating equipment is an immediate, serious hazard that risks potentially fatal carbon monoxide poisoning. Turn such equipment off and call for expert advice. Severe smoking and soot puffback from oil fired heating equipment is also dangerous and requires immediate action.
  • Improper heating system maintenance, such as failure to adequately clean and inspect the heating flue, furnace, or boiler, unsafe heating safety devices (e.g. relief valves), evidence of sooty, noisy operation, leaks in fuel, air, water. An example of an easy-to-spot clue that an oil fired heating system needs service and cleaning is illustrated at DRAFT REGULATORS, DAMPERS, BOOSTERS
  • Improper Heating System Construction/Installation
  • Leaks in the hot water heating system - see BOILER LEAKS CORROSION STAINS and LEAKS at BASEBOARD, CONVECTOR, RADIATOR.
  • Loss of heat - no heat - is discussed just below at How to Diagnose Loss of Heat With Oil-Fired Hot Water Heating Systems
  • Missing Heating System Components or missing or damaged heater safety controls, operating aids
  • Noises in heating systems are discussed at How to Diagnose Noises during Heating System & Oil Burner Operation
  • Heat won't turn off: see Heat Won't Turn Off - Stop Unwanted Heat for an explanation of why heat may continue to come out of radiators or baseboards even though you have turned down the thermostat
  • Heating system operating pressure or temperature are abnormal - see BOILER PRESSURE & TEMPERATURE SETTINGS
  • Heating system reliability - Unreliable heating systems or heating systems at or near the end of their useful life. Home inspectors and qualified heating inspectors should not give a heating system a passing grade just because heat is entering the building. The heating system needs to be safe, and sufficiently reliable that the owner can reasonably expect to leave the building without a likely loss of heat and related building damage. If a heating system has less than a year of remaining reliable and safe operating life, it is in unacceptable condition.
  • Heating System Damage: leaks, mechanical damage, combustion chamber damage
  • Heating System oil burner noise, smoke odors are discussed at Oil Burner Noise, Smoke, Soot, Odors - Diagnosis & Cure
  • Clues of potential other heating system defects: leaks, corrosion, stains, abnormal temperature or pressure, high heating fuel bills

How to Diagnose Loss of Heat With Oil-Fired Hot Water Heating Systems

  • Does the heating equipment have electric power?: make sure that electrical power is on for all of the heating system components. Check local switches at the boiler, wall mounted boiler switches at the stairwell down to the basement or utility room or in other areas, and check the circuit breakers or fuses in the electrical panel.
  • Is there fuel for the boiler ?: check the oil tank gauge; if the boiler or furnace is fired by natural or LP gas check that no one has shut the supply valves. If a system has been "shut down" and you don't know when or by whom this step was taken, beware of turning the heating system back on without an inspection and safety check by an expert technician. If you're out of oil call your oil company and request an emergency delivery. Usually the delivery person will also need to enter the building to bleed air from the oil lines in order to get the oil burner operating again.
  • Does the oil burner start but then shut off? Is the system "off on reset"? if so the red "reset" button will have popped up on the oil burner control (or possibly on an electric motor operating the oil burner) and the system has an operating problem and needs service. It may be possible to re-start an oil burner that has turned itself off by pressing the red reset button ONCE. If the system re-starts and runs acceptably, you can have heat while waiting for the service technician but the system still needs inspection, service, and possibly other repairs before it can operate safely and reliably. If you push the reset button and the burner does not start and keep running for five minutes or more, DO NOT try again as you may flood the system with oil and make restarting difficult and dangerous. Also see OIL BURNER INSPECTION & REPAIR
  • Boilers-Hydronic Heat: Is hot water water circulating?
    • Check the hot water circulator: Test to see if the circulator is operating Feeling the hot water distribution piping (Watch out it should be HOT!). Feeling the piping can indicate if circulator is running or not -- a quick change in temperature means the circulator works; slow change in temperature may occur if the circulator does not work but hot water is circulating by convection.
    • Check hot water baseboards: if some baseboards are hot and others cold, are they all on the same heating zone? If not, are all of the thermostats turned up? If some heating baseboards are hot and others cold and we're sure that they're on the same zone, then the system is probably air-blocked.

      A heating circulator pump is capable of pushing water around in the loop of heating baseboard but is often not capable of overcoming a section of baseboard that contains a large bubble of air. It's necessary to remove such air blocks. If air blocking has been recurrent a previous owner may have installed air bleeders at strategic points.

      The bleeder can be opened slightly and carefully, to permit air to escape. As soon as water starts coming out of an air bleeder valve it can be closed. Automatic air purge devices are available and are usually installed right at the heating boiler but sometimes additional ones are needed at higher levels in the building.
    • Check hot water radiators or convectors: if some radiators or wall convectors are hot and others are cold, and provided that the individual feed valves located at each of these devices is open (turned counterclockwise) the radiator or convector may be air blocked. Usually an individual air bleed valve is located on each of these devices. As we suggested above, if your hot water heating system is running (the steam or hot water boiler is making noise and seems to get hot) but some of your radiators or baseboards are cold, see RADIATORS and AIRBOUND HEAT SYSTEM REPAIRS.

How to Diagnose Noises during Heating System & Oil Burner Operation

Complete details about all types of heating system noises, causes, cures, are found at HEATING SYSTEM NOISES. Noises specific to an oil burner used at heating boilers or water heaters are discussed at OIL BURNER NOISE SMOKE ODORS. Excerpts below focus on some of the most common heating system noises.

  • Noises during oil burner startup - a "bang" or puffback which blows soot into the room through the barometric damper or through other equipment openings: the oil pump may not be shutting down properly at the end of an oil burn cycle, leaking incompletely burned oil into the combustion chamber. That oil ignites at startup causing a potentially dangerous puffback. Immediate service and repair are needed. See OIL BURNER SOOT & PUFFBACKS
  • Noises during oil burner startup - a "rumbling" sound (which usually continues all during operation" or a "stumbling" sound in the combustion chamber probably indicates that the system needs inspection and cleaning very soon. Some noise is normal however, but the normal sounds tend to be more smooth and continuous. See OIL BURNER NOISE SMOKE ODORS
  • Noises during oil burner shut-down - a stumbling or rumbling after the oil burner motor has stopped, indicate that oil is continuing to leak into the combustion chamber and risks a dangerous puffback - see "Noises during oil burner startup" above. Immediate service is recommended. See OIL BURNER NOISE SMOKE ODORS
  • Noises of shrieks or grinding coming from the electric motor or oil pump on the oil burner or more rarely at a circulator pump mean that prompt service is needed - probably a bearing is failing.
  • Startup problems: noises and clues of puff back: if you see flapping at the barometric damper or if you see or hear vibrations in the system, prompt service is needed -see OIL BURNER SOOT & PUFFBACKS.
  • Noisy hot water heating system piping or circulator pumps: can be caused by air in the piping (AIRBOUND HEAT SYSTEM REPAIRS) or by (more rarely) a defect in the circulator pump itself (Circulator Pumps & Relays)
  • Noises from radiators or heating baseboards:
    • Clanking heating system pipes or sharp snapping noises may be heard as a normal consequence of expansion of metals during the heating cycle. These noises can often be eliminated or reduced by careful routing of piping and by allowing room around heating pipes for expansion, but probably not eliminated in the case of hot water baseboards.
    • Bubbling or rumbling heating system noises in hot water heating piping can be caused by air in the heating lines. If the amount of air becomes excessive the heating system may be unable to circulate hot water and extra steps to bleed unwanted air will be required. See AIRBOUND HEAT SYSTEM REPAIRS
    • Hissing heating system sounds such as air escaping from radiators or the piping where air bleeder valves are installed are normal but should be brief and uncommon. If you constantly hear air hissing from radiator bleed valves double check that you understand what kind of heat you have - hissing from bleeder valves on steam heat radiators as heat is coming up in the building is normal. See RADIATORS.
  • Also see OIL BURNER INSPECTION & REPAIR

Evaluate Heating Boiler Leaks & Corrosion

When observing evidence of leaks on a heating boiler, keep these points in mind:

  • Even serious leaks may never show up as "wet" spots: A boiler may be leaking but you may see no actual water: during the heating season the boiler may always be hot, causing small leaks on the boiler or on heating piping to simply evaporate. But such leaks will usually be visually very evident: look for a build-up of corrosion, green or white or other colored mineral salts, or look for rust or water stains on the equipment.
  • Internal heating boiler leaks: Some critical boiler leaks may be internal and not visible by simple inspection, such as a leak inside the boiler heat exchanger which may pass water into the combustion chamber. A service technician or a skilled home inspector should be able to spot evidence of these leaks.
  • Surface rust, light, superficial rusting, is generally repairable. Clean the area and fix the leak when the boiler is next serviced and monitor for any future leaks.
  • Exfoliation, or thick flaking rust on any boiler but particularly on a steel heating boiler is very serious, possibly not repairable, and risks loss of the boiler as well as sudden loss of heat in the building.
  • Leaks related to temperature or pressure: Some leaks occur only at peak operating temperature - e.g. at relief valve. On some heating boilers such as some cast-iron units, leaks may occur between boiler sections when the system is cold - on these models some technicians prefer to keep a little heat in the boiler year-round to avoid this problem. Leaks between boiler sections may be repairable but if left unattended can destroy the equipment.

See BOILER LEAKS CORROSION STAINS and LEAKS at BASEBOARD, CONVECTOR, RADIATOR for details.

A Catalog of Common Heating System Leak Points - Where to Watch for Heating System Leaks

  • Tankless Coil mounting plate - see rust stains below and around plate
  • Pipe fittings at face of coil plate - mineral salts
  • Leaks around bolt openings - suspect hidden damage
  • Leaks between sections of a cast iron boiler
  • Leaks at the circulating pump mounting flanges
  • Leaks at the boiler temperature/pressure relief valve. This leak may be very dangerous as corrosion from water passing through the valve may prevent its safe operation in an emergency. Prompt expert inspection and repair are needed. Watch for leaks below the valve's mouth or discharge pipe (a pipe should extend from the relief valve to a few inches from the floor) or watch for corrosion at the tip of the discharge pipe. Gently feel inside the tip of this pipe to see if it's wet. DO NOT TRY TO TEST or open or operate the relief valve itself.
  • Leaks at air bleeder valves - at the boiler or remote where such bleeders are placed on heating piping or baseboards or radiators
  • Leaks at radiator control valves
  • Leaks at poorly-soldered copper pipe fittings on finned copper baseboard heating systems
  • Leaks due to frozen and burst piping or in extreme cases, frozen and burst heating boilers themselves

How to Recognize & Diagnose Inadequate Combustion Air, Sooting, or Burn Marks at Oil-Fired Heating Systems

Backpressure sooting at an oil fired furnace (C) Daniel Friedman Backpressure Burn at an oil burner (C) Daniel Friedman

Lack of adequate combustion air (see COMBUSTION AIR ) can be indicated by or can result in these heating system operating and heating system safety worries:

  • Improper oil burner system operation such as noises, rumbling, etc. discussed above. See BOILER NOISE SMOKE ODORS for the conditions listed here.
  • Oil burner sooting or dirty operation (the photo at above-left) may be due to improper adjustment of the oil burner or draft, a blocked chimney, or other problems. Also see Draft Inducer Fans as their use may indicate a chimney, draft, or venting problem.
  • Burn marks on the boiler (photo at above right), furnace, or water heater, (these conditions may be caused by a blocked exhaust flue and inadequate venting).

    Safety Warning: burn marks on a heating boiler or furnace (shown in our page top photo) can also be due to collapse or damage to the combustion chamber liner - a serious fire hazard needing immediate attention. Notice that in our photo at right, the brown burn marks around the oil boiler combustion chamber inspection port (that rusty round door above the oil burner) have been cleaned-off.

    The presence of these burn marks does not necessarily mean that the oil burner backpressure problem remains - in this case the system has been cleaned and adjusted, but no one has re-painted the front of the boiler. But if you see fresh peeling paint or soot in such an area further investigation is needed.

    That's why we recommend that after repairing a back-pressure problem at heating equipment the service technician should clean the boiler or furnace exterior - to remove confusing debris and to make it easier to see if the problem recurs.
  • Heating equipment located in a small utility room with no provision for combustion air intake. When the service technician adjusts the system she probably worked with the utility room door open, but when the service tech left the job he may have closed the door - completely changing the availability of combustion air for the equipment. We need about one square inch of un-louvered (unobstructed) combustion air intake per 1000 btuh of the oil fired heating boiler, furnace, or water heater. See COMBUSTION AIR and also COMBUSTION AIR for TIGHT buildings
  • Increased heating system operating cost, - see HEATING COST SAVINGS METHODS
  • Damage to oil burner components (backpressure heat can destroy an ignition transformer),
  • Loss of building heat - the heating system stops working, see HEATING LOSS DIAGNOSIS-BOILERS and HEATING LOSS DIAGNOSIS-FURNACES
  • Noises at the heating system when the boiler, furnace, or water heater starts, is operating, or is shutting down. See How to Diagnose Noises during Heating System & Oil Burner Operation
  • Smoke indoors,coming out of the heating equipment or its draft regulator. See BOILER NOISE SMOKE ODORS for the conditions listed here.
  • Carbon monoxide or combustion gas and flue gas leaks: potentially, the production of carbon monoxide or other flue or combustion gases which escape into the building - potentially dangerous. See CARBON MONOXIDE - CO and CARBON MONOXIDE WARNING as well as CHIMNEY INSPECTION DIAGNOSIS REPAIR.

Also see Unsafe Air Conditioning or Heating Duct Openings which describes the risks of reduced combustion air on hot air heating systems when certain return air duct defects are present, and also see CARBON MONOXIDE - CO and CHIMNEY INSPECTION DIAGNOSIS REPAIR

A Guide to Heating Equipment Malfunctions & Their Implications

  • Noises & soot buildup can lead to a potentially dangerous puffback which can damage the heating equipment and blow soot and smoke throughout the building.
  • Leaks on hot water heating systems are never acceptable, anywhere.
    • Leaking pressure/temperature relief valves need immediate attention and repair (Leaking relief valve could be due to water-logged expansion tank, improper control settings (temperature too high), improper automatic water feeder operation (pressure too high), or defective valve (leaky). True, you only have to report the valve.
    • Did you miss problems at the other components?)
    • Corroded relief valves also need to be test by a service technician and repaired or replaced as they may be unsafe and may fail to open when necessary
  • Relief Valves: Do not touch the heating boiler or water heater temperature or pressure relief valve - it may open and fail to shut down. A relief valve which does not work is dangerous since the system is missing an important safety device. Should an over pressure or over temperature condition develop for other reasons, the boiler could explode.
  • Corrosion on heating system parts: Do not pick at corrosion as you may start a catastrophic, un-stoppable leak requiring total system shut-down. Leaks left un repaired can destroy heating equipment.
  • Tankless coils for making hot water:
    • If there is different water pressure/flow observed in the kitchen in which the hot water pressure is significantly less than cold, even before examining the building's mechanical systems you may speculate that a tankless coil installed may be installed.
    • What other clues suggest that the local water supply may be hard in minerals and that there may be a risk of clogged piping?
    • When the water supply is high in minerals, the hot water pipes or tankless coils clog up before cold water piping. Is a water softener installed? Is there known "hard" water--have mineral deposits clogged the coil?
    • Are there "cleanout" plumbing fittings on the tankless coil piping? Does this suggest a history of clogging and acid-flush treatments?
    • A clogged tankless coil can be repaired or replaced.
    • How severe was that rust you observed at the tankless coil mounting plate? Severe rust may mean that the boiler must be replaced.

Examples of Heating System Defects with Important Implications

  • Lack of adequate combustion air can result in improper system operation, sooting, loss of heat, noises, smoke, and potentially, the production of carbon monoxide or other flue or combustion gases which escape into the building - potentially dangerous
  • Leaky oil at an oil burner ignition transformer: watch for back pressure in combustion chamber--watch out for blocked heating flue or blocked chimney - these would be unsafe, or the heater may be unreliable. An unreliable heater can lead to frozen burst pipes and costly building damage. A blocked chimney could lead to a potentially fatal carbon monoxide hazard.
  • Leaks in hot water or steam (condensate piping) heating systems risk
    • Loss of heat, frozen pipes, related damage
    • Water damage to the building including rot or costly mold contamination
  • Unusual interior moisture conditions, noises, smoke, or odors during heating season--watch for blocked chimney or poor flue vent connections
  • Equipment recalls: Specific heating system problem brands Repco, Blueray etc.
    [Do not confuse Repco™ heating boilers, which had fire chamber and other failures, with other products (REPCO pumps, REPCO controls, REPCO water conditioners, or water treatment that carry the Repco name. Those products are distinct from REPCO heating boilers and are produced/distributed by the R.E. Prescott Company. Further, we are unaware of any remaining warranty or replacement support for failed or antiquated Repco heating boilers.]
  • BLUE vs YELLOW COMBUSTION FLAMES - the Blueray history and blue flame vs. yellow flame combustion, flame color & combustion efficiency, & how oil competes with gas as a heating fuel.
  • Blueray Heating Boilers/Furnaces Safety Recall by the US CPSC, with additional history, photos, and technical details; Blue Flame Blue Ray
  • Carbon Dioxide Gas Toxicity
  • Carbon Monoxide Gas Toxicity, exposure limits, building inspection for CO hazards
  • DUST, HVAC CONTAMINATION STUDY An Investigation of Indoor Dust Debris Blamed on a Heating/Cooling System Reveals Carpet Dust
  • Goodman Furnace High Temperature Plastic Vent HTPV safety recall US CPSC notice
  • Home Heating System Should Be Checked [for proper venting and for CO Carbon Monoxide Hazards - DJF]
  • Inspection Procedures for Oil-Fired Heating Systems Detailed step by step approaches for inspecting complex systems]
  • Lennox Pulse Furnace Safety Inspection/Warranty Program: Carbon Monoxide Warning
  • Oil Tanks - The Oil Storage Tank Information Website: Buried or Above Ground Oil Tank Inspection, Testing, Cleanup, Abandonment of Oil Tanks
  • Oil Tanks Above Ground, UL Standards, guidance for home owners, buyers, and inspectors
  • Home Inspection Report Language Library: Gas Fuel Piping or Tank Faults Basic advice - home inspection report language suggestions
  • Home Inspection Report Language Library: Buried Oil Tanks, Basic home buyer advice - home inspection report language suggestions
  • Home Inspection Report Language Library: Defects in Oil Tank Installations, Tanks, and Heating Oil Piping
  • Plastic Heating Vent Pipe & Other Heating Safety Recall Notices
  • Weil McLain Model GV Gas Boiler/gas valve CPSC recall/repair

Frequently Asked Questions (FAQs)

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Questions & answers or comments about diagnosing problems with residential hot water heating systems: the heating boiler

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

  • R.E. Prescott Company, a producer of other REPCO™ residential and industrial products as well as a provider of design-build engineering services is at 10 Railroad Avenue, Exeter, NH 03833. Tel: 603-722-04321 or 888-786-7482. Trish O'Keefe from Prescott informed us (10/7/2009) that their company had nothing to do with the failed Repco heating boilers discussed at InspectAPedia.com. She wrote:
    • Our company manufactures & distributes residential water treatment equipment, including our Repco line of conditioners. We have a plumbing & heating supply dept as well. We are mistaken for the Repco Boiler company on a regular basis, most frequently in Oct. and Nov.
    • Any information you could give me on the other Repco company would be appreciated. We've assumed it is no longer in business, and we'd like to know that for sure. Many callers want to know where to get replacement parts and I would be glad to direct them if I knew...plus there's always a chance they might be interested in a Crown Boiler instead.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

  • Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
  • Home Reference Book - Carson DunlopThe Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

    Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.

  • GO TO Carson Dunlop's Home Study Course Information - How to Become a Home Inspector: Carson Dunlop's nationally recognized Home Study Course, selected by ASHI the American Society of Home Inspectors and other professionals and associations. This website author is a contributor to this course.
  • GO TO Carson Dunlop's Home Study Course Information - How to Become a Home Inspector: Carson Dunlop's nationally recognized Home Study Course, selected by ASHI the American Society of Home Inspectors and other professionals and associations. This website author is a contributor to this course.
  • GO TO Carson Dunlop's Home Study Course Information - How to Become a Home Inspector: Carson Dunlop's nationally recognized Home Study Course, selected by ASHI the American Society of Home Inspectors and other professionals and associations. This website author is a contributor to this course.
    Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd
  • Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
    Special Offer
    : Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.

  • Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
  • DUST, HVAC CONTAMINATION STUDY An Investigation of Indoor Dust Debris Blamed on a Heating/Cooling System Reveals Carpet Dust
  • Fuel Oil & Oil Heating Magazine, 3621 Hill Rd., Parsippany, NJ 07054, 973-331-9545
  • Goodman Furnace High Temperature Plastic Vent HTPV safety recall US CPSC notice
  • Home Heating System Should Be Checked [for proper venting and for CO Carbon Monoxide Hazards - DJF]
  • Inspection Procedures for Oil-Fired Heating Systems Detailed step by step approaches for inspecting complex systems]
  • Lennox Pulse Furnace Safety Inspection/Warranty Program: Carbon Monoxide Warning
  • Oil Tanks - The Oil Storage Tank Information Website: Buried or Above Ground Oil Tank Inspection, Testing, Cleanup, Abandonment of Oil Tanks
  • Oil Tanks Above Ground, UL Standards, guidance for home owners, buyers, and inspectors
  • Plastic Heating Vent Pipe & Other Heating Safety Recall Notices
  • Weil McLain Model GV Gas Boiler/gas valve CPSC recall/repair
  • Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
  • National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
  • The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
  • Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
  • The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
  • Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
  • "Residential Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
  • "Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
  • "Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
  • Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
  • Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
  • Installation Guide for Residential Hydronic Heating Systems
  • Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
  • The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
  • Links to our list of additional information on heating system inspection, repair, maintenance
  • ...
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