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HEATING SYSTEMS

AFUE DEFINITION, RATINGS
AGE of CHIMNEYS & FIREPLACES
AGE of AIR CONDITIONERS & HEAT PUMPS
AGE of HEATERS, BOILERS, FURNACES
AGE of WATER HEATERS
AIR CONDITIONING & HEAT PUMP SYSTEMS
AIR FILTERS for HVAC SYSTEMS
AIR FLOW MEASUREMENT CFM
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 PREVENTER VALVE, HEATING SYS
BACKFLOW PREVENTER, HEATER WATER FEEDER
BACKUP HEAT for HEAT PUMPS
BAROMETRIC DAMPERS
BIOGAS PRODUCTION & USE
BLEVE EXPLOSIONS
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BLUE vs YELLOW COMBUSTION FLAMES
BLUERAY Recall
BOILERS, HEATING
BOILER CHEMICAL TREATMENTS
BOILER COMPONENTS & PARTS
BOILER CONTROLS & SWITCHES
BOILER LEAKS CORROSION STAINS
BOILER LEAKS, HOW TO LOCATE
BOILER NOISE SMOKE ODORS
BOILER OPERATING PROBLEMS
BOILER OPERATION DETAILS
BOILER PRESSURE & TEMPERATURE SETTINGS

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

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 VENT CONNECTORS
FREEZE-PROOF A BUILDING
FUEL OIL TYPES & CHARACTERISTICS
FUEL UNIT, HEATING OIL PUMPS
FURNACES, HEATING
FURNACE CONTROLS & SWITCHES
FURNACE EFFICIENCY, HIGH vs MID
FURNACE HEAT EXCHANGER LEAKS
FURNACE OPERATION DETAILS
FURNACE OPERATING TEMPERATURES

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 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 CONTROL for HEATING SYSTEMS
NOISE, PLUMBING CHECKLIST
NOISE, WATER HEATER

ODORS & SMELLS DIAGNOSIS & CURE
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
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 - Water Heaters
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

Oil burner oil line switch (C) Daniel Friedman Guide to Oil Burner Fuel Units
Heating Oil Pump Installation, Diagnosis, Repair
     

  • Oil burner fuel unit guide: how to inspect , diagnose, install, maintain & repair or replace the heating oil fuel unit "oil pump" used on an oil fired furnace, boiler, water heater, or other heating equipment
  • Brands & Properties: Danfoss/Sunstrand/Suntec & Webster Oil Burner Fuel Units
    • Single stage & two stage fuel unit operating capabilities
    • Commercial capacity oil burner fuel pumps
    • Oil Burner Fuel Unit Rotation Direction - CW vs CCW or left hand vs right hand
  • Installation & Adjustment Procedures for an Oil Burner Fuel Unit
    • What are the Connections or Ports on a Heating Oil Fuel Unit?
    • Single-line Heating Oil System Fuel Unit Oil Piping Connections, Hookups
    • Two Line Fuel Unit Heating Oil Pump Unit Hookups
    • Internal Fuel Unit Bypass Control - does the bypass plug go "in" or should it be "removed" ?
    • Typical Pressure Settings on Heating Oil Fuel Units
  • How to bleed air out of oil piping and oil burner fuel units
  • Oil burner fuel unit Annual Maintenance, Service & Repair Guide
    • Change-out of the Internal Filter Screen on Heating Oil Fuel Units
    • Vacuum Checks at the fuel unit
    • Internal Check Valve on Heating Oil Fuel Pumps: leaks, repairs, oil delay valves
    • Drive shaft connections for oil burner fuel pumps
    • Drive Shaft Bearing Leaks on Oil Burner Fuel Units
  • Questions & Answers about diagnosing, adjusting, repairing, or replacing heating oil fuel units or oil pumps on oil-fired heating equipment: boilers, furnaces, water heaters
  • References

Click to Show or Hide Related Topics

  • OIL BURNERS - home
  • COMBUSTION AIR
  • COMBUSTION AIR for TIGHT buildings
  • COMPLETE COMBUSTION, Stoichiometric
  • DIAGNOSE & FIX HEATING PROBLEMS-BOILER
  • DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
  • DRAFT MEASUREMENT, CHIMNEYS & FLUES
  • DRAFT REGULATORS, DAMPERS, BOOSTERS
  • ELECTRIC MOTOR OVERLOAD RESET SWITCH
  • NOISE DIAGNOSIS, HEATING SYSTEM
  • ODORS FROM HEATING SYSTEMS
  • OIL BURNER FUEL UNIT
  • OIL BURNER INSPECTION & REPAIR
    • Oil Burner Smoke Test
    • Oil Burner CO2 Test
  • OIL BURNER DELAY VALVE
  • 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 LINE CLOGGING FIX
  • OIL LINE QUICK STOP VALVES
  • OIL LINE SAFETY VALVES
  • OIL ODORS, LEAKY OIL TANK PIPING
  • OIL SPILL CLEANUP / PREVENTION
  • OIL TANKS - home
  • OIL TANK PIPING & PIPING DEFECTS - home
  • PUFFBACKS, OIL BURNER
  • SOOT on OIL FIRED HEATING EQUIPMENT
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Oil burner fuel unit installation & maintenance guide: this article describes the function, diagnosis, adjustment, and repair of oil burner fuel units or "oil pumps", and we provide related oil burner fuel unit safety, heating system efficiency and heating cost savings advice. We include a discussion of the oil pressure settings, one line vs two line oil piping connections, the location of the air bleeder valve, and the use of an oil delay solenoid valve or quick-stop valve or oil safety valve on some fuel units. We also describe common maintenance & repair topics & procedures for oil burner fuel units such as drive shaft coupling failures, drive shaft leaks, and internal check valve leaks.

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

Oil Burner Fuel Units or oil pumps: installation, inspection, diagnosis, maintenance & repair

Webster M34DK Fuel UnitAlso see FIRE SAFETY CONTROLS wHere we explain the proper and improper use of fusible link oil line valves - an improperly placed valve can cause leaks or even an explosion or fire at an oil-fired heating device oil pump fuel unit. The heating system articles provided at this website explain how to inspect and detect defects and hazards on heating systems, boilers, furnaces, and other equipment. Methods for saving on heating cost and on improving heating safety are included. Heating safety hazards such as carbon monoxide gas leaks, unsafe furnaces, furnace and boiler recalls are addressed. If you don't know what kind of heat your building uses, we explain how to figure out the answer at HEATING SYSTEM TYPES. If your heating system is not working properly, see NO HEAT - BOILER or NO HEAT - FURNACE.

The "oil pump", properly called the fuel unit in most oil heating texts, draws heating oil from the oil storage tank, pressurizes the oil to high pressures of 100 to 125 psi (typically on modern retention head oil burners), and delivers oil to the oil burner nozzle where the combination of high oil pressure, combustion air, and turbulating devices (in the nozzle and/or at the end of the oil burner) atomize the oil and spray it into the combustion chamber.

Danfoss/Sunstrand/Suntec & Webster Oil Burner Fuel Units

Webster single stage fuel unit (C) D FriedmanTwo common brands of widely used fuel units for oil burners are Danfoss Sunstrand or Suntec (photo at page top) and Webster (images at left and above-left). At left is a Webster single-stage 3450-rpm fuel unit.

Both companies make a range of excellent products that in our experience have proven durable and simple to install and maintain.

The single-stage Sunstrand J-pump and the two-stage Sunstrand H-pump were among the most widely used fuel units we encountered when servicing heating equipment in the Northeastern U.S. Webster's M-series fuel units are also widely used as OEM equipment on a variety of oil burners found on residential heating boilers, furnaces, and water heaters.

Single stage & two stage fuel unit operating capabilities

Quoting from Webster's description of their current product line we can read the typical capabilities of modern heating oil fuel pumping units:

Single and two stage models with 1725 and 3450 rpm operation feature compact design and field-proven reliability. These units, rated @ 3 to 25 gph (11 to 57 1/hr.) @ 100 psi (6.9 bar), can be used on one or two pipe installations. ... Operating pressure [on heating oil fuel units] is factory [typically] set at 100 psi.

Commercial capacity oil burner fuel pumps

Larger, commercial-application fuel pumps are of course also available, such as Webster's R-series fuel pumps that can deliver up to 75 gph and even V-pumps capable of firing equipment at up to 260 gph (gallons per hour) - far larger than any home application.

Oil Burner Fuel Unit Rotation Direction - CW vs CCW or left hand vs right hand

Fuel units for oil burners are sold in "left-hand" and "right-hand" rotation to meet different electrical motor and oil burner configurations. The direction of rotation is interpreted by viewing the fuel unit from the shaft end.

Installation & Adjustment Procedures for an Oil Burner Fuel Unit

What are the Connections or Ports on a Heating Oil Fuel Unit?

Suntec basic ports & connections - courtesy Suntec Fuel Units

As we describe and illustrate (Suntec ports and components are illustrated at left, courtesy Suntec - click to enlarge) in this article a typical fuel unit or "heating oil pump" will have these connections and controls:

  1. An inlet port - feeds oil from the oil tank into the pump or fuel unit
  2. Oil delivery pressure to the burner (adjustment screw)
  3. Oil return or outlet port or external bypass port - can be used in a two-pipe hookup to return oil to the oil tank
  4. Pressure gauge port
  5. Nozzle line port - high pressure oil delivered to the oil burner nozzle
  6. Heating oil inlet port
  7. An internal bypass port or cover - possibly accessed through the bypass port, an internal plug can be installed or removed
  8. Air bleeder valve

These features will be reversed if the fuel unit rotation direction is reversed, and they may be in different positions on different models and brands of oil burner fuel units. Not directly accessible from outside the fuel unit are additional important parts found on most heating oil pumps (or if you want to sound like a pro, call it a "fuel unit").

  • An internal check valve (discussed below)
  • An internal filter screen (maintenance or service item on most units, discussed below)

Single-line Heating Oil System Fuel Unit Oil Piping Connections, Hookups

Single line heating oil hook up (C) D FriedmanWhere an indoor oil storage tank is installed on or close to the same level as the oil burner, it is common for a single heating oil line to bring oil from the oil storage tank to the fuel unit. In a single-line installation, an internal check valve found in the fuel unit prevents oil backflow into the oil lines when the fuel unit stops spinning.

In our fuel unit photo (left) the green arrow marks the incoming oil from the oil tank and filter (under vacuum when the pump is running). The red arrow indicates the high pressure oil being delivered from the fuel unit into the oil burner nozzle line.

This oil burner pump unit includes an oil delay valve , an electric solenoid switch connected through the burner tube over to the oil burner motor run circuit by an electrical wire. (yellow arrow).

The typical fuel unit used on modern oil burners does not have a high lift capacity - perhaps 6 feet would be a safe lift level for a one-line oil pipe installation.

Watch out: we have found single-line fuel unit hookups where a low or even a buried oil tank was installed. Such systems may "work" successfully for many years even though they violate good practice. Or the single-line hookup may work only if the oil level in the oil storage tank is kept pretty high (reducing the total lift required). But on occasion we visited a property where there was recurrent loss of heat - a problem that was traced to the oil burner losing prime in the oil line. The "fix" was to convert the system to a two-line oil pipe hookup described below.

Two Line Fuel Unit "Heating Oil Pump" Unit Hookups

Two line heating oil fuel unit hookup (C) D FriedmanA two-line fuel unit hookup simply means that there are two oil pipes between the fuel unit and the oil tank. One line is the delivery line - from oil tank into the fuel unit, and the second line is the "return line" through which excess oil pumped by the unit flows back to the oil tank.

A two line oil piping system, required for buried oil tanks or oil tanks located below the oil burner, increases the "lift" capacity of the fuel unit and also nearly eliminates oil piping priming problems.

Our photo (left) shows a two-line oil piping hookup on a Suntec fuel unit - it's pretty easy to see since both the supply oil pipe and the return oil pipe connections are visible at the bottom of the fuel unit.

The oil inlet hookup is on the left and the oil "bypass" or "return" hookup is on the right. The label on the heating oil fuel unit face also will identify the various ports on the device.

A third oil pipe, the high pressure line from the pump outlet to the oil burner nozzle assembly is not clear in this photo, though you can make out a small brass tubing loop at the upper left in our photo - a part of the high pressure oil line.

Where a buried oil storage tank is installed or where the oil storage is significantly lower than the oil burner a two-line oil piping hookup is used to give added lift capacity to the fuel unit.

Watch out: check the fuel unit installation instructions and be sure that the internal check valve is set to the proper condition on the fuel unit when changing from a one-line to a two-line oil piping hookup, or vice versa.

Watch out: as we discuss at FIRE SAFETY CONTROLS and at OIL LINE SAFETY VALVES, when a two-line oil piping system is in use, the fusible link oil safety valve should be installed only on the oil supply line. A check valve without a fusible link is typically installed on the oil return line.

Internal Fuel Unit Bypass Control - does the bypass plug go "in" or should it be "removed" ?

Webster oil burner fuel unit (C) D FriedmanWatch out: standard factory-set-up usually delivers a fuel unit with an "internal bypass" in the fuel unit "open". That's the set-up for a one-pipe oil piping hook-up.

When installing a two-pipe oil piping hookup to a fuel unit, an allen screw or plug is inserted into the fuel unit to close the internal bypass. The access to the internal bypass will be found beneath a service plug and will usually also be marked on a label on the fuel unit body.

A single-pipe heating oil system requires that the bypass plug is removed. Leaving the plug in the fuel unit will result in a blown seal, and oil leak, and loss of heat.

A two-pipe heating oil system requires that the internal bypass plug is inserted - in place. But kinked oil piping or piping blocked by sludge in the return line can still result in a blown seal in the fuel unit, an oil leak, and loss of heat. [8]

If a novice heating tech is having trouble remembering what to do with a bypass plug or port, just remember that we want only one excess pumped-oil return path - it's either inside the pump itself (an internal bypass is open on a one pipe oil piping system) or it's outside the pump and sends excess oil back to the oil tank (the internal bypass is then shut).

Our photo (above left) shows a modern single-stage 3450 rpm Webster fuel unit. If you are replacing the fuel unit on an oil burner you will need to note and match the following specifications:

  • The rotation speed of the unit (1725 or 3450 "high speed")
  • The direction of rotation (some pumps may be convertible) as "left hand" or "right hand" rotation direction.

Dirty oil burner pump fuel unit (C) D FriedmanAt the bottom of the label in our photo above you can see a reference to the internal bypass plug along with a warning note and an arrow pointing to the threaded "plug" that is either installed (internal bypass closed, two pipe installation) or removed (internal bypass open, one pipe installation).

Our fuel unit at left, also a Webster unit, tells a story without having performed any tests. It appears from the dirt and cobwebs that no one has touched this device - a clue about its service history.

Typical Pressure Settings on Heating Oil Fuel Units

When we (DF) serviced heating equipment back in the dark ages, typical fuel unit pressure factory setting was to 100 psi. The pump output can be adjusted on most fuel units, typically within a range of about 100 psi up to 150 psi. At oil burner school we learned to set the fuel unit pressure up to 110 or even 120, adjusting the nozzle size down to a smaller gph nozzle to keep the overall fuel delivery rate at the intended design point for the oil burner. That higher pressure gave better, finer oil spray delivery and more efficient oil burner operation.

Currently we see new oil fired heating equipment using 125 psi as a "standard" pressure setting. Modern fuel units such as the Webster M34DK fuel unit is able to maintain its 3 gallon fire size throughout the 100 to 150 psi pressure range.

Our heating service tech Bob, from Bottini Oil, recently installed a replacement fuel unit on our lab's oil burner assembly. In setting up the system, a 15 year old cast iron Peerless boiler with a Beckett oil burner, Bob set the oil pressure up to 140 psi, and the smoke was set first to "trace" and then (with a slight combustion air boost) down to "zero" - what he regards as current optimum settings for contemporary high speed oil burner units on newer heating equipment.

How to bleed air out of oil piping and oil burner fuel units

Two line heating oil fuel unit hookup (C) D FriedmanIn the oil burner fuel unit shown at left, our pen is pointing to the air bleeder valve on this fuel unit, in the center right of our photo.

Beckett points out in their oil burner installation instructions that it is essential to vent air out of the oil piping and out of the fuel unit itself during installation. You'll see a rounded fitting that looks suspiciously like an automobile brake system bleeder valve installed on fuel units for that purpose.

We attach a clear plastic tube to the fitting, put the other end of the fitting into a clear jar where we can watch for the end of air bubbles, then run the system to pump oil and air through the fuel unit until no more air bubbles are occurring.

This same procedure may be necessary if an oil fired heating system has run completely out of oil.

There are two reasons why this air bleeding operation is essential:

  • If too much air is inside the piping and fuel unit the pump will become air-locked and it won't deliver heating oil to the oil burner nozzle
  • Even if the piping is delivering oil to the oil burner, air in the system expands after the oil burner stops, pushing un-burned oil into the combustion chamber causing dirty, noisy oil burner start-ups (as that old un-burned oil is ignited), and risking a dangerous or damaging oil burner "puffback" later.

Air Bleeding the Fuel Unit on a One-Pipe System

  1. Start the oil burner and arrange the primary control for continuous burner operation. That can be as simple as jumping the thermostat terminals, or if the boiler is hot, running all of the heating zones so that the boiler won't shut down at its high limit during this operation.
  2. Turn the bleed valve counter clockwise about 1/2 turn for fast air purging. We attach a 1/4" I.D. plastic hose that empties the air/oil mix into a container. If you use a clear container (don't break it or you'll have a mess) you can immerse the end of the tub in heating oil and you can see when air bubbles stop coming out of the tube.
  3. How long you need to bleed air depends on where air is suspected in the system (between tank and oil burner or just at the filter, for example) and the length of oil piping involved. If necessary you can prime the fuel unit by pouring some clean heating oil in to the unit through the cover inlet port.
  4. Continue bleeding the unit for 15 seconds after the last air is seen. If you are hasty, Suntec and other manufacturers warn that the system may not work properly.
  5. Stop the air bleed procedure by tightening the bleed valve screw clockwise. CW.
  6. Clean the unit thoroughly and run the burner, inspecting for leaks.

Two pipe oil burner systems do not normally need to be air- bled since the fuel unit will return any excess air along with oil down the return line to the oil tank.

Annual Fuel Unit Service & Repair Guide

Change-out of the Internal Filter Screen on Heating Oil Fuel Units

Oil burner fuel unit filter screen (C) D FriedmanOil burner fuel units typically use an internal filter/screen to help protect the pump internal parts and the oil burner nozzle. While a proper heating system installation will include a canister-type oil filter on the oil piping ahead of the oil burner, for several reasons debris can escape the filter and enter the oil pump body.

This screen should be replaced as part of annual oil burner service. The screen comes with a new gasket that should also be used.

Watch out: if you fail to properly torque the four bolts holding the fuel unit cover over this screen assembly, air leaks in and oil leaks out at that location will prevent proper fuel unit operation.

Debris-clogging at the oil burner check valve

Watch out: when the fuel unit screen is never replaced, debris entering the oil pump can cause two common operating problems, both leading to improper and even unsafe oil burner operation:

Debris can clog the oil burner check valve (discussed just above) causing the valve to fail to stop oil delivery quickly when the oil burner stops running. The result can be a sloppy oil burner shut-down, oil burner nozzle clogging, and loss of heat or an oil burner puffback

Debris that prevents the internal check valve from closing may also allow oil from an oil storage tank to feed through the fuel unit by gravity, flooding the combustion chamber and risking a dangerous oil burner puffback, explosion or fire when the system re-starts.

During a service call on a very old oil burner in Poughkeepsie, NY in the 1980's, we found a low-speed oil burner that would keep right on going even after we turned off electrical power to the oil burner motor. It was scary. The combination of heating oil feeding past the failed check valve and into the combustion chamber along with very hot combustion chamber liner components was enough to keep a "fire" going in the combustion chamber of the old boiler.

Vacuum Checks at the fuel unit

Annual service for the fuel unit also includes a vacuum check for proper pump operation and to check for leaks in the input line.

Internal Check Valve on Heating Oil Fuel Pumps: leaks, repairs, oil delay valves

An internal check valve on the fuel unit is designed to rapidly stop the flow of oil out of the pump and to the oil burner nozzle when the electric motor stops spinning. If the check valve is not working, as the electric motor shaft slows below its full operating speed, oil may be otherwise delivered to the oil burner nozzle at low-pressure.

In turn, low pressure oil delivery means incomplete combustion of the oil in the combustion chamber (it is not fully atomized or broken into a fine spray). Incomplete combustion of heating oil in turn clogs the oil burner nozzle, leading to sooting and even loss of heat or a dangerous oil burner puffback.

Because a failed or "sticking" oil burner pump check valve causes serious operating problems and because this internal part is not easily repaired in the field there are two common repair approaches:

  1. Replace the entire oil burner fuel pump or fuel unit
  2. Install an oil delay valve - see OIL LINE QUICK STOP VALVES for details. An oil delay valve is an electric solenoid installed on the high pressure oil line between the oil pump outlet fitting and the oil burner nozzle tube. The oil delay valve can help assure clean oil burner start-ups and shut-downs by making sure that the electric motor spinning the oil burner air intake blower as well as the oil pump are up to full operating speed before the solenoid opens to allow oil to flow to the oil burner nozzle.

We provide an article series that explains the installation & use of

  • Fusible Link Oil Safety Valves,
  • Vacuum-Activated Oil Safety Valves, OSVs & PRVs,
  • Check Valves on Heating Oil Lines, and
  • Tigerloop™ or similar oil line de-aerator/prime-protection devices.
  • Oil delay valves, also called quick-stop valves and also referred to as oil safety valves, are discussed separately at OIL LINE QUICK STOP VALVES.

Drive shaft connections for oil burner fuel pumps on boilers, furnaces, water heaters

An electric motor mounted on one side of the oil burner drives a shaft that in turn spins both a combustion air blower (that draws combustion air into the oil burner tube) and the fuel unit. Both of those components are connected in line on the drive shaft of the electric motor using a somewhat flexible rubber or plastic and rubber coupling.

Older "slow speed" oil burners used a motor that rotates at 1725 rpm, a speed that in turn determines the speed of the blower assembly and the fuel unit as well.

Modern "high speed" oil burners use a motor that rotates at 3450 rpm, a bit noisier but because of the additional combustion air that these systems can provide, high speed burners typically operate at a higher efficiency than the older models.

Watch out: a stripped or failed or loose coupling can result in slow burner blower assembly or fuel unit rotation and improper oil burner operation, or in no oil burner operation at all. A bad coupling or bad coupling alignment (everything should be in a straight line, motor, blower shaft, fuel unit shaft) will also be a cause of noise at the oil burner or fuel unit.

Drive Shaft Bearing Leaks on Oil Burner Fuel UnitsLeaky shaft at the oil  burner fuel unit (C) Daniel Friedman

Damaged coupling joining the electric motor that drives the oil burner, the combustion air blower squirrel cage fan, and the shaft that turns the fuel pump unit itself.

In our photo, left, the heating service tech has removed the fuel unit (oil pump) from the oil burner to inspect for evidence of leaks around the oil burner's fuel unit drive shaft.

He did so after observing oil and debris and tar inside the burner tube assembly and on the oil burner's squirrel cage fan assembly. Because this fuel unit had a (small) leak around the fuel unit shaft, the entire unit was replaced. In this closeup photo of the fuel unit shaft leak you can see a tarry accumulation that convinced the tech (and us) of the leak problem.

What happens if we have even a small leak around the fuel unit drive shaft on an oil burner pump? Oil dripping into the oil burner tube soils the squirrel cage blower fan blades just enough that the blades accumulate and hold dust and debris. The result is that while the fan may look ok, it is moving less air, leading to inadequate combustion air and a smoky sooty oil burner operation, eventually perhaps a puffback. Crud accumulating in the oil burner tube will eventually clog a small bleeder hole in the tube bottom, leading to still more oil and debris accumulation in this location.


Frequently Asked Questions (FAQs) about heating oil fuel units (oil pumps)

Question: What causes pulsating oil pressure at the oil burner?

Since I asked for one, my oil burner has a pressure gauge mounted on the unit showing the output pressure on the system. Usually the gauge is steady at 120 psi but now I see the needle is waving all over the place. What might be wrong. .

Reply:

I would be a little nervous about leaving a gauge on the outlet side of a fuel unit for heating oil equipment. There is a risk of blowout of the gauge and a horrible oil leak mess. That said, look for:

  • a defective oil pressure gauge (check against a known-good gauge)
  • an air leak in the intake oil supply piping line
  • an air leak on the fuel unit itself. For example if someone pulled the fuel unit cover to replace the strainer and failed to install a new gasket, or failed to properly tighten the cover, you could get an air leak there. [8]

Other leaks and problems besides those air leaks above can also lead to oil burner shut-down or improper oil burner nozzle cutoff problems, including:

  • Leaks at the heating oil filter cover, oil piping fittings, or air bleeder screw.
  • Air trapped between the oil cut-off valve (oil safety valve) and the oil burner nozzle. Usually this problem will disappear with a few oil burner on and off cycles as long as new air is not leaking into the system.
  • A partly clogged strainer on the inlet end of the oil burner nozzle. If the strainer is fully clogged the system won't start at all;
  • A leak at the nozzle adapter. The nozzle adapter is a brass fitting that connects the oil burner nozzle to a small diameter oil supply tube that runs inside the oil burner gun assembly. If you are heavy handed and over-tighten a steel oil burner nozzle in the end of the nozzle adapter, or if you mess up the other end of the adapter where it threads onto the end of the oil supply tube, you may get oil spray leaks out at the fitting, causing havoc with the oil burner flame. I know, I made this mistake badly a time or two before I (DF) learned not to over-tighten these parts during oil burner assembly.

Incidentally, Suntec also offers these additional diagnostic suggestions regarding heating oil pressures: [8]

If oil pressure at the outlet side of the fuel unit is low, check the accuracy of the pressure gauge, then check that the nozzle capacity is not greater than the capability of the fuel unit. We add: check that someone has not misadjusted the fuel unit pressure screw.

Improper oil burner nozzle cut-off diagnosis - here is a diagnostic procedure from Suntec:[8]

With a pressure reading gauge in the nozzle port of the fuel unit (that is the fuel unit's output side), watch for a minute to see what happens to oil pressure as the oil burner stops running.

  • If the pressure reading drops from normal operating level (say 100 to 140 psi depending on how the fuel unit was set) down to a lower number, then stabilizes, the system is working normally and the sloppy oil burner shut down is most likely due to air in the system.
  • If the pressure unit drops all the way to 0 psi, the fuel unit is defective and needs to be replaced.
  • Also see Oil Delay Solenoid Valve or Quick-Stop Valve on Oil Burner Pumps / Fuel Units and see OIL BURNER SOOT & PUFFBACKS

Ask a Question or Search InspectApedia

Questions & answers or comments about diagnosing, adjusting, repairing, or replacing heating oil fuel units or oil pumps on oil-fired heating equipment: boilers, furnaces, water heaters

Ask a Question or Enter Search Terms in the InspectApedia search box just below.

Technical Reviewers & References

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

  • [1] Audels Oil Burner Guide, Installing, Servicing, Repairing, Frank D. Graham, Theo. Audel & Co., New York 1946, 1947, 1955 (out of print, copies occasionally available from antique book dealers and on EBay)
  • [2] Beckett Model SR Oil Burner Instruction Manual, R.W. Beckett Corporation, PO Box 1289, Elyria OH 44036 and R.W. Beckett Canada, Ltd., 430 Laird St., Guelph, Ontario, Canada N1G 3x7
  • [3] Thanks to Bottini Fuel service technician Bob for discussing the buzzing aquastat relay problem, 4/18/2012. Bottini Fuel is a residential and commercial heating oil distributor and oil heat service company in Wappingers Falls, NY and with offices in other New York locations. Bottini Fuel, 2785 W Main St, Wappingers Falls NY, 12590-1576 (845) 297-5580 more contact information for Bottini Fuel
  • [4] Beckett Model SF Oil Burner Instruction Manual, op.cit.
  • [5] Sunstrand Corporation - Sunstrand Fuel Units, 4949 Harrison Avenue P.O. Box 7003 Rockford, Illinois 61125-7003 U.S.A. Telephone: (815) 226-6000 Fax: (815) 226-5399 http://www.sundstrand.com
  • [6] Sunstrand Transmission Service Manual, May 1974, web search 08/19/2011, original source: http://www.cushmantrackster.com/pay-pdfs/sundstrand.pdf - Sunstrand Series 15 hydrostatic transmissions
  • [7] Webster Fuel Pumps & Valves, Capitol City Tool, Inc., http://www.websterfuelpumps.com/
  • [8] Suntec Model A-7400 Fuel Unit Solenoid Dumping Pump,
    Suntec Industries Inc., 60 Aberdeen Drive - PO Box 5000 Glasgow, KY 42142-5000 - USA Tel : 270 651 7116 - Fax : 270 651 9276 e-Mail : info@suntecpumps.com and
    Suntec Industries France, 1 Rue Lavoisier - B.P. 102 F-21603 LONGVIC Cedex - FRANCE Tel : +33 (0)3 80 70 60 70 - Fax : +33 (0)3 80 70 61 11 e-Mail : information@suntec.fr, [copy on file as /heating/Oil pumps fuel units/Sunted_Solenoid_DumpingPPump.pdf] ,
    Also /Suntech_Solonoid_Safety_Valves.pdf (brochure)
    web search 4/19/12, original source: http://www.suntecpumps.com/Suntecus/PDFs/Form%202740%20
    -%20Solenoid%20Dumping%20Pump.pdf
  • [9] Suntec Model PRV-38 Oil Safety Valve Installation Information, Suntec Industries Inc., 60 Aberdeen Drive - PO Box 5000 Glasgow, KY 42142-5000 - USA Tel : 270 651 7116 - Fax : 270 651 9276 e-Mail : info@suntecpumps.com and
    Suntec Industries France, 1 Rue Lavoisier - B.P. 102 F-21603 LONGVIC Cedex - FRANCE Tel : +33 (0)3 80 70 60 70 - Fax : +33 (0)3 80 70 61 11 e-Mail : information@suntec.fr, [copy on file as /heating/Oil pumps fuel units/Form 2155 - PRV-38 Installation.pdf]. You can download this file from Suntec's website.
  • Fuel Oil & Oil Heating Magazine, 3621 Hill Rd., Parsippany, NJ 07054, 973-331-9545
  • Inspection Procedures for Oil-Fired Heating Systems Detailed step by step approaches for inspecting complex systems]
  • OIL TANK PIPING & PIPING DEFECTS - how to pipe oil tank fill, vent, and oil supply lines, common defects, leaks, safety concerns
  • 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.)
  • "Scale formation in water heaters and methods of prevention", Krappe, Justus Maximilian, Engineering experiment station. Gas engineering bulletin; no. 6; Research series; no. 74; On cover: Engineering bulletin, Purdue university. Vol. xxiv, no. 3a. June, 1940 (Layfayette Indiana) commonly referred to in some references as "Purdue University Bulletin No. 74" - thanks to researcher Robyn Goldstein for the full citation. LCCN: 40028844 & OCLC: 1038544 - Water analysis, water softening, hot-water supply. 27pages. You can obtain this document through your local library. (full copy file at InspectAPedia 3/31/2010) Purdue B074 can be hard to locate online.
    Also Bradford White Corporation (a manufacturer of water heaters) has published excerpts from that document, available at Purdue_B074_BradfordW.pdf
  • ...

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    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
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