Oil Burner Won't Run

Diagnose & Repair an Oil Burner that won't start or won't run properly

Step 1: Make These Quick Visual Checks 

• Power switched off to the unit
  
  - ELECTRICAL POWER SWITCH FOR HEAT
• A fuse or circuit breaker or fusible switch has blown
• Adequate oil supply in the oil tank
  
  - OIL TANK GAUGES
• The oil supply valves are all open
  
  - OIL LINE QUICK STOP VALVES
  
  and
  
  - OIL SUPPLY LINE SAFETY VALVES, OSVs
• The thermostat is really calling for heat - it is switched to "heat" and proper time of day
• The room temperature is below the thermostat set temperature
  
  - THERMOSTATS, HEATING / COOLING
• Evidence of an oil-flooded combustion chamber (you do not want to try turning on the burner in this condition as there is danger of a horrible puffback mess)

Step 2: Oil Burner Electrical Power Tests

First: test for voltage across terminals 1 & 2 at the stack relay or cad cell relay primary control

If there is no Voltage at the Oil Burner

• Check the LIMIT SWITCH, BOILER,
  
  check
  the RESET SWITCH, HEATER PRIMARY CONTROL,
  
  Check
  the LOW WATER CUTOFF VALVE (if it's hot water heat or steam heat),
  
  check any fusible switches,
  find and check all of the electrical switches that can turn off the unit (the stair switch, the service switch, the breaker or fuse in the panel
  
  - ELECTRICAL POWER SWITCH FOR HEAT.
• AMPS MEASUREMENT AUTOMOTIVE DC
• AMPS MEASUREMENT METHODS
• DMM DIGITAL MULTIMETER HOW TO USE
• VOLTS / AMPS MEASUREMENT EQUIP
• VOLTS MEASUREMENT METHODS

If Voltage is Present at the Oil Burner

Continue oil burner troubleshooting with Step 3 below

Step 3: Thermostat Tests

If you are calling for heat at the thermostat (set to HEAT mode and set to a temperature well above the actual room temperature) and if the burner oil burner does not fire up at all there may be a problem with the thermostat or the 24V thermostat circuit so that there is no call for heat.

You may need to change the 24V transformer or the thermostat.

Let's rule out a problem with the thermostat or its wiring by "bypassing" the room thermostat altogether.

At the primary control remove the existing thermostat wires and connect a jumper wire across the two T T terminals.

This completely eliminates the room thermostat and the thermostat wires between the thermostat itself and the primary control from the system.

So with a jumper in place across the two T T terminals at the heating system primary control, if the oil burner starts and runs normally we suspect a thermostat or thermostat wiring problem.

In that case continue at OIL BURNER STARTS & RUNS but NOT PROPERLY

Thermostat installation, troubleshooting, and repair details begin

at THERMOSTATS, HEATING / COOLING - home

Or see this ARTICLE INDEX to HVAC THERMOSTATS for a complete list of installation and diagnostic procedures.

Step 4: Oil Burner Start & Run Diagnostic Steps

If the oil burner relay pulls in and

The oil burner starts, continue at Step 4a below.

• Check the oil burner flame for normal appearance,
  
  The system seemed to run OK when you jumped the TT terminals, right?
  
  If the flame is normal (not smoky or loud rumbling or intermittent) reconnect the thermostat as we describe just below.
  
  If the oil burner flame is not normal,
  
  
• Re-connect the room thermostat
  
  Remove your thermostat jumper, wirere-connect the normal thermostat wires to the T T terminals, and make sure the thermostat calls for heat.
  
  

  If the burner runs OK & does not again go off on reset or "lock out" then continue with the steps just below at 4a.
  
  If the oil burner will not start and run then continue with the steps below at 4b - Oil Burner Still Does Not Start

Step 4-1: Oil Burner Runs, Not short cycling and not making unusual noises, odors, or soot

If the oil burner starts on a call for heat and runs normally without noises, soot or smells, then the heating system system should be OK.

On a furnace the burner will usually run continuously until the fan limit or thermostat turn it off.

On a hot water or steam boiler the burner may run until the boiler temperature reaches the HI limit on the primary control aquastat, then will turn back on when the boiler temperature drops. This cycle will continue until the room thermostat is satisfied.

On an oil fired water heater the burner will run until the temperature sensor on the heater detects that the set temperature in the water heater has been reached.

But if the oil burner runs but not properly, continue with the steps below on this page.

Step 4-2: Oil Burner Runs but Short Cycles On/Off

Is the oil burner short cycling on-/off every couple of minutes or less?

This condition can lead to the oil burner going off on safety-reset.

Your service tech will probably check the following:

• Check for loose wires at controls, power, thermostats &c.
• Check for hot or burned relay switch contacts
• Check also for improper voltage.
• For a furnace whose oil burner short cycles,
  
  Check first for anything that is restricting the airflow through the system, causing the plenum to overheat.
  
  Typical causes include a dirty air filter or blocked, obstructed, damaged air ducts, or a very dirty air handler blower squirrel cage fan, or a loose drive belt on the air handler blower or failing air handler blower motor.
  
  Check also for a damaged or soot clogged temperature sensor on a stack relay control or a damaged fan limit control switch
  
  If none of thes is the problem check for/replace the blower fan control relay itself.
• For a heating boiler there could be a problem with the aquastat or its temperature settings - check the aquastat HI, LO and DIFF settings
  
  at AQUASTAT CONTROLS
• For a steam boiler, check the low water cutoff switch (that can also bounce) if one is present
  
  - LOW WATER CUTOFF VALVE
• Check for room thermostat for a bad heat anticipator setting or for thermostat bounce or thermostat internal wiring or flat cable connection defects
  
  - HEAT ANTICIPATOR Adjustment (if present) If the problem is along-standing one, check first for improperly-set heat anticipator at the room thermostat or if the problem is recent, for a failed heat anticipator devicve or circuit (not all thermostats use a heat anticipator)
  
  - THERMOSTATS, HEATING / COOLING has more room thermostat diagnostic procedures
  
  - Check the room thermostat for improperly set HVAC cycle or swing temperature variation
  
  - THERMOSTAT SWITCHES, INTERNAL
  
  If all of these look ok, you may need to change the primary control relay.
  
  Thanks to HVAC tech Anthony Alaggio for suggestions about oil burner short cycling.

  Example of short cycling oil burner problem fixed by replacing the thermostat (bad heat anticipator)

  My Heil Lincoln series fuel oil furnace recently started short cycling.

  The burner would kick in run for less than a minute, then kick back off.

  The blower wouldn't run until 20 seconds after the burner shut off.

  I eventually traced the problem back to the thermostat, a Honeywell T87F.

  The anticipator must have developed a short and wouldn't respond to any adjustments I made.

  Replaced it with a programmable Lux t-stat with an adjustable deadband (swing).

  Your website made troubleshooting this problem go very fast. Thanks! On 2016-11-20 by Luke H

  Example: of oil burner short cycling safety warning

  We have an older weil mclain gold high efficiency heater.

  Recently, it has started to go on for fifteen to twenty seconds, stop and then restart for another fifteen to twenty seconds and so on.
  
  Every time it does this, we hear a clicking sound when it goes on and another when it goes off.
  
  Our cast iron water radiators only get lukewarm to the touch even though the thermostat is turned up 5 degrees over the room temperature.

  We have a call out to our plumber but we were wondering if our system is safe to run. (Jan 2, 2018) Deb
  
  (Mod) Replied
  
  Deb

  Short cycling in any oil burner can cause soot buildup that causes the problem to get worse until the system has trouble starting at all.

  Watch out: your system needs service promptly. Turn it off. SHORT CYCLING oil burners can end in loss of all heat or
  
  also OIL BURNER SOOT & PUFFBACKS

Step 5: Oil Burner fires but just intermittently - oil burner chatters

• Check for loose electrical connections at all power and control wiring connections.
  
  Here is an example from reader M.F.

  ... the furnace draft fan began to pulse several times upon starting.

  After making sure the control module showed a steady green, I asked a friend and he suggested that I wiggle all the spade connectors to be sure there is good contact between the copper and aluminum.
  
  It seems that there only needs to be a little corrosion to cause problems.

  That seems to have done the trick. - M.F. 12/24/2014

  
  

Step 6: Oil Burner Still Does Not Start or Starts but then Stops and won't re-start

Oil burner starts but stops and the reset button pops on the primary control

Watch out: the system is not working safely and needs repair but you might be able to keep it on if the burner runs for 5-10 minutes or longer when teh reset button is pressed or the stack relay switch is reset

See details at

RESET SWITCH, CAD CELL RELAY 

or at

STACK RELAY SWITCH 

If the oil burner motor runs, continue below with Step 4b.

If the oil burner motor never even starts to run, contue at Step 4c below.

Step 7: After Reset, If the oil burner fires up but goes off on reset again

Watch out: if you pressed the reset button on the primary control and the oil burner turned off again in a few minutes or less, DO NOT keep pressing the reset button. Doing so risks a dangerous puffback explosion.

• Check for a bad flame, bad firing, dirty nozzle, electrodes, oil leak at the nozzle adapter, blocked combustion air
• If a stack relay is used, check for a dirty or broken helix
• If a cad cell relay is used, check for a dirty or failed cad cell eye
• If these look OK you probably have to change the primary control relay

Details are at OIL BURNER SOOT & PUFFBACKS

Step 8: Oil burner motor started but no flame: no oil flow

• No oil flow comes out of the burner. 
  
  You already checked that there is really oil in the tank, right?
  
  - OIL TANK GAUGES
• Check that the oil tank float gauge is not stuck.
• Check for a dirty or clogged oil filter
  
  - OIL FILTERS on HEATING EQUIPMENT
• Check for a dirty, clogged oil burner nozzle
  
  - OIL BURNER NOZZLES [PDF]
• Bleed the fuel unit of any trapped air, then check the pressure (pressure out, vacuum in) on the oil lines.
• Check any oil safety valves, check valves, PRVs,
  
  OIL SUPPLY LINE SAFETY VALVES, OSVs
• Check for a clogged strainer in the oil burner fuel unit
• Check that the burner motor is turning the burner blower and fuel unit (a bad coupling or a bad motor)
• Check for an oil line that is clogged or blocked by ice (outdoor tank) or sludge - a clue is to see how much crud is in the bottom of the oil filter canister.
  
  OIL LINE CLOGGING FIX
• If there is oil flowing freely at the oil line and all of the above check out, we suspect that the fuel unit is not pumping.

Step 9: Oil Burner Started, Oil Delivered, No Ignition

Check Ignition Transformer & Electrodes

No ignition: oil comes out of the nozzle but there is no ignition. Check

• Check for voltage 
  
  at the primary, control, terminals 2/4 or if your oil burner uses constant ignition, terminals 2/3
• Test the ignition transformer 
  
  for spark (old timers know a screwdriver trick; if the flame is blue and reaches mostly across the gap of the transformer springs with the screwdriver an inch or so away, the transformer is probably ok.
  
  Watch out: this is very high voltage: you could be shocked or killed - this old-timer's trick is not officially recommended and our service tech declined to be photographed performing this step.
  
  Other, recommended oil burner ignition transformer test procedures are provided by the manufacturer.
  
  If the transformer is weak the spark will be dead, not bridge the gap to the screwdriver, or not extend to at least 3/4 the width between the contact springs, or will be orange not blue in color.
  
  In my photo above we found burn marks on the boiler that might indicate backpressure in the combustion chamber - an operating snafu that can direct heat back up the oil burner tube until it destroys the ignition transformer - described in more detail
  
  at IGNITION TRANSFORMER FAILURES
• If the transformer does not check out,
  
  replace it.
• If the transformer looks OK Check the oil burner electrodes and ceramic insulators
  
  heck closely the ignition leads including for cracked shorting ceramic insulators in the burner assembly or an improper or improper gap or damaged electrodes.
  
  You already looked to be sure the electrodes were not bridged with soot and crud, right?
  
  See details at OIL BURNER ELECTRODES

Step 10: Oil Burner Motor Never Starts

Step 10-1: If the oil burner motor does not start

• Check primary terminals 2 & 3
• Check for live voltage
  
  at wires powering the motor (if no power there and the relay pulled then there may be a broken wire)
• Check for thermal overload:
  
  If hot and ground are good at the motor, check for a thermal overload switch pop on the motor itself - if it's out, let the motor cool, reset it and start again.
  
  RESET SWITCH, ELECTRIC MOTOR
• Oil Burner Motor Tests
  
  If after reset of the thermal overload the motor still won't start, replace the motor.
  
  At ELECTRIC MOTOR DIAGNOSTIC GUIDE
  
  we describe both offline and online electric motor circuit analysis (MCA) test procedures.

Step 10-2: If the primary control relay does not pull in to turn on the oil burner

• If the primary control is a stack relay, re-step the relay contacts inside the control.
  
  STACK RELAY SWITCH
• If the primary control is a cad cell relay or aquastat, check the lock switch on that device: see
  
  AQUASTAT RESET BUTTON
  
  RESET SWITCH, CAD CELL RELAY
  
  RESET SWITCH, HEATER PRIMARY CONTROL
• Check for cold relay points - broken, not connected
• Check for a broken or clogged helix in the stack relay
• Check for a bad cad cell relay