Photograph of  a modern oil-fired heating boilerNo Heat Diagnosis
for Oil or Gas Fired Hot Water Heating Boilers

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Heating boiler problem diagnosis and repair guide - no heat or loss of heat calls: Here we explain how to recognize & diagnose no-heat problems with residential heating boilers, including loss of heat, heating boiler noises, leaks, odors, or smoke, and high heating costs.

This article explains the diagnosis and correction of no heat conditions for water or hydronic or hot water or radiator or baseboard hot water heating systems.

We give help in troubleshooting heating systems using LP gas (propane) or natural gas. How to inspect & repair central hot water heating boilers - hydronic heating. Baseboard, radiator, convector heat inspection, defects, repairs.

This website answers questions about all types of heating systems, advising on troubleshooting, inspection, diagnosis, and repairs. 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 also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

How to To Diagnose a "no heat" problem: steps the occupant or owner can take before calling repair

Heaing system emergency switch (C) Daniel FriedmanHot Water Heating System: Once you confirm that your heat is made by hot water (a heating boiler) you might want to review hot water or "hydronic" heating systems


at BOILER OPERATING STEPS where we describe the parts and operating sequence of hot water heating systems.

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


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?

How to Diagnose Loss of Heat With Oil-Fired or Gas-Fired Hot Water Heating Systems - hydronic heating system troubleshooting

If the heating boiler oil burner is not turning on at all check the causes listed on this page. We'll take you through photo-illustrated step by step things to do when you have no heat and you need to determine what's wrong. First let's review these simple "no heat" concepts .

NO HEAT: BURNER OFF, SAFETY NOT TRIPPED: - Oil or gas burner has stopped, no safety switch is tripped

1. Is the thermostat calling for heat? check that the room thermostat setting is at least 5 degrees above the actual room temperature.


2. No electrical power: check that all of the switches that power on the oil or gas burner are in the "on" position. Check heating circuit fuses & circuit breakers, not just the wall switch. We discuss this in detail just below.

3. Is there fuel in the oil tank or LP gas tank? Check your oil tank or LP gas tank tank gauge.

Out of heating oil? If the marker in your oil tank gauge reads 1/8 full or less, or is at the bottom or out of sight you are probably out of oil. If your oil tank is buried, and if you do not have an indoor (remote) fuel level gauge, the oil level is checked in the tank by removing the tank filler pipe cap and using a long (clean) stick (or in emergency a clean string and weight) to measure the depth of heating oil in the tank.

Remember that a problem with the oil piping, oil filter, or fuel unit can also cause no oil to be delivered to the oil burner even if plenty of oil is in the tank.

See OIL BURNER FUEL UNIT for some helpful diagnostics

Out of LP liquid propane gas? Check the gauge on your propane tank. If the reading is 10% or less you are out of fuel.

If your boiler is fueled by piped-in natural gas from a utility company, check that the company hasn't turned off your gas supply at the gas meter - something that might happen if you didn't pay a gas bill or if the gas company thought your building's gas system was unsafe.

4. Electric motor problem at the burner or blower fan: Check that an electric motor (for the oil burner, gas burner, or blower assembly) reset switch may have tripped. See our notes above about electric motors, and


5. Aquastat or cad cell control or relay trouble: if you hear or have ever heard buzzing from any heating system control that includes a relay switch, watch out for a control cover that is in contact with a relay switch in the unit.

If the cover is lightly touching the relay switch the control may simply buzz when the relay is trying to move.

But a too-tight control cover can also prevent a relay from operating, leading to loss of heat. Simply pulling off the cover to let the relay move freely can immediately discover and "fix" this problem.

Details and illustrations including diagnosing buzzing relays are


NO HEAT: BURNER HAS TURNED OFF ON SAFETY: Oil or gas burner has stopped, the safety switch is "off" or "tripped"

If you are not sure how to find and check the safety control reset buttons on your heating system, we describe these controls in more detail just a bit further on in this article.

The burner on your heating boiler, furnace, or water heater has shut down, if a red "reset button" has popped up on the burner primary control or on an electric motor that operates the system. This condition is called "Safety Off".

Watch out: Before re-setting the safety switch or button, it's a good idea check the following five common causes of loss of heat leading to a Safety Off condition. Photos and details follow these short paragraphs.

How to press the heating system reset button: If you do not see anything wrong, you can try re-setting the heating system: press and hold the red reset button down for 3 seconds and release it. If the heating system has electricity it will try to re-start.

Watch out: If the system does not keep running smoothly don't keep pressing the reset button - that could flood the combustion chamber with unburned fuel, causing a dangerous puff-back. Just press the reset button once. If the heating system starts and runs ok, you still should request a service call, but you can have heat while you're waiting.

1. Heating fuel failures - out of oil in the oil tank, clogged oil filter, clogged oil nozzle, oil line has been bent, crimped, clogged, clogged oil pump strainer (fuel unit strainer), or inability of the fuel unit to pump oil (broken motor shaft, missing internal bypass plug on a two line oil tank system, an air leak in the oil inlet line, or a leaky foot valve in the oil tank causing loss of oil prime). if the oil tank is outdoors in freezing weather the oil in the tank or in an oil line may have become waxy or jelled.

2. Oil burner motor failure: the electric motor that runs the oil burner may itself have gone off on reset. Some causes of electric motor failure: one pipe oil system with the bypass plug installed in the fuel unit (oil pump) causing excessive pressure and stalling the motor; centrifugal motor switch sticking (try banging on the motor once); motor condenser burned out; motor stator or internal windings burned or shorted; motor bearing failure.

Try re-starting the motor -

3. Oil burner ignition failure: the oil burner's ignition transformer terminals are loose; the electrodes on the burner nozzle are dirty or not set to the proper gap; the oil is contaminated and is hard to ignite; the ignition transformer has become weak or has burned out (look for tar oozing out of the ignition transformer container); the oil burner nozzle is clogged preventing oil from contacting the ignition spark arc; the ignition electrode(s) are grounded on the air tube of the burner;

4. Faulty heating system control operation: the safety sensor that checks that a good oil burner flame has been established is not working; a stack relay spring or cad cell eye may be dirty with soot; the stack temperature may be too low for the stack relay (boiler is under-fired); the oil burner has been cycling on and off to frequently (a problem with the thermostat).

Tip: Look for loose electrical connections: before deciding that a control or switch has failed, confirm that the system has electrical power, all switches are on, and that a wiring connection has not come loose.

On a recent no-heat call we were embarrassed to learn from Bob, the service tech, that the problem was most likely that somebody (who me?) may have accidentally knocked loose the electrical connector at the oil delay valve (aka "quick stop valve").

The connector may still appear to be in place but may have been pushed slightly back or askew. The result is that on a call for heat the oil burner motor will run but the burner will never ignite. Details about loose connector diagnosis & cures for the quick stop valve or oil delay valve or the PD Timer are

Other common loose electrical connections might be at wiring to any heating control or at the oil burner itself.

5. Irregular stack temperatures: in the flue can cause oil burner draft and temperature or control problems. Downdrafts (missing chimney cap), insufficient draft due to chimney problems, or fluctuating oil burner flame may be at fault. Also

-- some of this material is paraphrased from Audel.

Oil Burner Operating Problems: Oil or Gas Burner rough, noisy, smoky, smelly

The heating burner operates but not properly.

Next let's check each cause of no heat in detail; if your system uses warm air heat instead of water or steam, review the check-items just below before going

SAFETY WARNING: If a heating system oil burner has been deliberately "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.

Heaing system emergency switch (C) Daniel Friedman

Is the heating boiler turned on? Is there electric power to all of the heating system components such as an oil burner at the boiler and power to the circulator pumps?

Photograph of an oil fired heater stack relay

Where are all the heating system reset buttons? If you are looking for the main reset button on heating equipment you'll want to

and CAD CELL RELAY SWITCH (hot water boilers and some water heaters),

Stack Relay Switch
On older oil fired boilers and furnaces,

SPILL SWITCH, FLUE GAS DETECTOR (gas fired equipment),

and Low Water Cutoff Controls On steam heating systems.

At ELECTRIC MOTOR OVERLOAD RESET SWITCH we discuss the thermal overload switch and reset button that is found on many electric motors including those operating air conditioning fans, heating system oil burners, and furnace blowers and motors.

A Stack relay switch may be installed on the flue vent connector and may be in the "safety - off" position. To identify and reset this control see STACK RELAY SWITCH. Stack relays are found on older oil fired furnaces and boilers.

Still no heat? Once you have assured that you have heating fuel and that electrical power is turned on to the heating unit, if you still don't have heat check these controls:

How to Diagnose Soot or Noises during Heating System & Oil Burner Operation

For full details of this topic be sure to

How to Evaluate Heating Boiler Leaks & Corrosion

For full details of this topic see BOILER LEAKS CORROSION STAINS

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

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

How to Recognize & Diagnose Inadequate Combustion Air for Oil-Fired Heating Systems

Heating system combustion air sketch Carson Dunlop Associates

For full details of this topic see INADEQUATE COMBUSTION AIR

Lack of adequate combustion air can result in improper system operation, sooting, increased heating cost, damage to oil burner components (back pressure heat can destroy an ignition transformer), higher and more frequent heating service costs, 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

Safety warning: The sketch shown here, courtesy of Carson Dunlop, explains how dangerous furnace back-drafting can occur when there is insufficient combustion air.

These conditions can not only release flue gases into the occupied space, but they are likely to cause the production of potentially fatal carbon monoxide.

We've seen heating equipment that seemed to work just fine during its adjustment because the service technician was working with the door to the furnace or boiler room open. But when she left the system and closed the furnace room door, suddenly there was insufficient combustion air.

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


A Guide to Heating Equipment Malfunctions & Their Implications

Examples of Heating System Defects with Important Implications


Continue reading at BOILER OPERATING PROBLEMS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see DIAGNOSE & FIX HEATING BOILER, FAQs - questions & answers posted originally at this page.


Or see GAS PIPING, VALVES, CONTROLS if your heating system is fueled by LP or natural gas

See HEATING SYSTEM TYPES if you don't know whether your heat is provided by a furnace (hot air) or boiler (hot water), or steam boiler (steam heat) or whether your fuel is oil, gas, or electric, and whether your heat is hot water, steam, or warm air

Or see this

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