Martin Cooke, Technical Director at EOGB Energy Products Ltd, provides guidance on correctly replacing oil burners, fault finding and servicing…


When problems arise with an oil boiler it is often down to age. However, as long as the boiler is sound and the water jacket and/or heat exchanger and electrical controls are still in good condition, problems may be caused by one or more of the components on the burner.


Of course everything has a working life and components such as ignition transformers and oil solenoids which operate at high temperatures can eventually fail or fail intermittently causing nuisance lockouts. These parts are still available to replace as many burners fitted over the past twenty years or so are industry standard and have ignition transformers, oil pumps with solenoid and photocell.


The engineer working on the appliance often needs to weigh up the pros and cons of fixing versus replacing the burner unit. For example, if the burner requires a new fan motor, fan and oil pump then you could easily be approaching the cost of a replacement burner, especially if you factor in the labour costs involved. Burner manufacturers will be able to advise on a suitable burner replacement for the boiler model, and then the engineer can make the decision on what is the best plan of action.


Burner replacement tips


Often burner replacement is relatively simple and a retrofit burner can be a quick solution to get the boiler back up and running, plus you are able to offer the customer a warranty from the burner manufacturers. However there are a few essential questions that must be answered before replacing a burner, such as:


  • Is the oil supply the fundamental problem for burner failure? If it is a gravity fed oil supply then remove the flexible hose from the oil pump on the original burner and see if you have a flow of oil at this point. This is a common fault that gets overlooked and it could just be a simple fuel filter blockage
  • Do you know the model and output of the boiler? This may sound obvious but many old boilers still in operation are devoid of essential information such as data plates
  • Does the old burner have a non-standard extended blast tube?
  • Is the correct nozzle for the boilers output already fitted?
  • Is standard wiring used for the electrical connections? Don’t pull out wires on the old burner before checking what they do and where they go. This can turn a simple job into a problem job very quickly!
  • Does the new burners’ mounting flange fit the boiler? Most manufacturers offer a six bolt flange to give a few options when it comes to mounting. Don’t destroy the old one getting it off before you are certain that the new one will fit!

Fault finding


If an engineer is new to fault find on an oil burner, a simple methodology is to follow the burner sequence of operation. The burner sequence of many common burners is:


  1. Fan purge
  2. Spark
  3. Photo cell check for stray light
  4. Power to solenoid coil
  5. Fuel release ignition
  6. Photo cell checking for flame
  7. Preparation until thermostat is satisfied

Then check if the burner is locked out or sat waiting for a signal to run. The control box neon indicator will display when a lockout has occurred but if there is no light on the control box then check the electrical supply to the burner. Most oil burners have a simple 220 volt AC supply down to the control box or terminal strip on the burner so if no voltage is present then check the thermostat, overheat stat, frost stat, or time clock before undertaking any work on the burner as the fault may be external.


Before starting work always fit a pressure gauge to the oil pump as this will tell you if you have the pressure adjusted correctly. You don’t want to work on the burner for an hour only to discover you have no oil pressure to start with! This is also a good indication that the drive coupling between the pump and the motor is connected and not stripped out.


Identifying the fault


When you press the reset does the fan run and then the burner locks out before igniting? Remove the burner and check if the blast tube is wet with fuel. If so, then it is probably ignition transformer failure or electrode problems. If the tube is dry it could be solenoid coil on oil pump or photocell detecting ‘stray light’.


Try disconnecting photocell and firing the burner again. If the burner lights then locks out after ten seconds, replace the photo cell. If the burner doesn’t ignite after disconnecting the photocell, check the solenoid coil. This could be checked with a multi-meter on ohms resistance and if you get open circuit then replace solenoid. If the burner runs for a few seconds and lockouts it is most likely a photocell failure. If the burner runs for a few minutes and lock out then it could be an oil pump solenoid failure.


These are a few of the common oil burner failures that are relatively easy to rectify. If an engineer is new to oil, most manufacturers offer oil burner training courses to go over the commissioning, serving and fault finding procedures.


Servicing quick guide


Domestic oil boilers should be serviced every twelve months. Check manufacturer’s instructions and relevant local authority legislation regarding oil storage and ensure the following is checked or changed where necessary:


  • Replace nozzle
  • Replace braided hose (if it’s a long life hose check date on hose and replace if there is any doubt on its age)
  • Check external filters and replace elements if they are a disposable type
  • Follow manufacturer’s instructions on boiler baffle removal and cleaning of combustion chamber and condense trap if applicable
  • Fit pressure and vacuum gauges to ensure pressure and flow of oil to burner
  • Check combustion as per manufacturers guidelines including a smoke test prior to analyzing
  • Complete a suitable service report displaying combustion figures including, CO2, CO, O2, smoke number and flue gas temperature

By following the correct guidelines above, installers can ensure that they make a quick and accurate diagnosis to effectively repair the heating system and minimise shutdown time.