OFTEC Oil Firing (OFT101/105E) common mistakes
OFTEC Oil Firing (OFT101/105E) · Understand the traps and how to avoid them.
Treats the fire valve as the primary overheat protection and cannot state where the fire valve must be fitted relative to the burner and oil line, or what temperature it operates at.
Candidates group all safety devices together and memorise 'fire valve' without separating its function (isolating the oil supply on fire/overheat) from the appliance overheat thermostat and high-limit stat.
What to do instead
Build a three-column table of safety devices: what it senses, what it does, and where it is fitted. For the fire valve, commit to memory that it sits on the oil line outside the building, is normally held open by a fusible element or capillary phial, and closes on a rise to a set temperature.
Calculates ventilation openings from appliance kW input using the wrong formula or forgets that a boiler and an open-flue appliance in the same space require combined free area.
Ventilation is taught as a rule-of-thumb, so candidates apply a remembered figure without checking whether it applies to the appliance type (room-sealed vs open-flue) or the total rated input.
What to do instead
Work every ventilation question from first principles: state the appliance type, total input, required free area per kW, and whether high- and low-level openings are both needed. Show the arithmetic so a slip is visible.
Misreads flue draught readings, quoting a positive pressure or a reading taken at the wrong point, and cannot distinguish a balanced flue from an open flue when deciding test method.
Candidates learn that 'draught should be negative' but do not practise interpreting readings taken at the flue test point versus the terminal, or appreciate that room-sealed appliances are tested differently.
What to do instead
Practise reading a draught gauge on both flue types, record where the sample is taken, and state the expected sign and magnitude for each. Always identify the flue category before selecting the test.
Confuses the roles of the control thermostat, the overheat/high-limit thermostat and the burner control box, so fault-finding stops at 'the boiler won't fire' without a logical sequence.
Candidates jump to the control box because it is the most visible component, skipping the simple checks (power, thermostat call, photo-cell, solenoid) that would isolate the fault.
What to do instead
Use a fixed diagnostic sequence: supply and controls, then thermostat call, then burner motor and pump, then ignition, then flame detection. Write the sequence down and apply it to every fault scenario.
Gives the wrong smoke number or CO2 target for a pressure-jet burner, or treats a high smoke number as acceptable because CO2 looks right.
Candidates remember 'low smoke is good' but not the actual acceptance limits, and do not connect excess air, smoke and CO2 as a single combustion picture.
What to do instead
Learn the smoke scale and the acceptable band, and the CO2 range for kerosene pressure-jet burners. Practise explaining how reducing excess air raises CO2 but also raises smoke, and why the smoke limit governs.
Describes oil storage tank siting without stating the required separation from buildings, boundaries and drains, or omits bunding and secondary containment for a domestic tank.
Tank siting is a list of numbers candidates skim; without a mental map of the installation they cannot recall which separation applies to which hazard.
What to do instead
Draw a plan view of a tank installation and label each separation (building, boundary, drain, flue terminal) and the bund capacity rule. Reconstruct the drawing from memory before answering siting questions.
Cannot explain why kerosene and gas oil differ in preheat requirement, viscosity and storage behaviour, and applies gas-oil settings to a kerosene appliance.
Fuel properties are treated as background reading rather than as the reason burner nozzles, pumps and preheaters are set as they are.
What to do instead
Link each fuel property to a burner consequence: viscosity to nozzle size and pump pressure, waxing point to storage and line protection, calorific value to combustion air. State the fuel before quoting any burner setting.
Omits a step in the commissioning and handover sequence, typically the combustion analysis after setting the air, or the recording of readings and instructions to the user.
Candidates learn commissioning as a jumble of tasks and lose the order, so the final verify-and-record stage is dropped under time pressure.
What to do instead
Memorise commissioning as a numbered flow: pre-checks, oil pressure and nozzle, air setting, combustion readings, safety device tests, then record and hand over. Rehearse the flow until the order is automatic.
Describes a service as 'clean and reassemble' without naming the components inspected, the tests performed after reassembly, or the reason each step matters.
Servicing is seen as practical routine rather than an examinable procedure with specified checks and post-service verification.
What to do instead
Write a service checklist that names each component (nozzle, electrodes, photo-cell, baffles, flueways, filters, fire valve) with the check performed and the test after reassembly. Answer service questions from that checklist.
Cannot trace a wiring diagram or state the function of the burner control box sequence, and misidentifies which terminal the thermostat, photo-cell or solenoid connects to.
Electrical controls are learned as component names rather than as a circuit, so candidates cannot follow a fault through the control box lockout sequence.
What to do instead
Redraw the burner circuit from memory: supply, control box, thermostat, motor, solenoid, ignition, photo-cell, and mark the lockout path. Practise tracing a fault to a terminal on a blank diagram.