OFTEC OFT105 Commissioning: What the Record Covers, Combustion Analysis and Handover to Customer

Quick Answer: OFTEC OFT105 is the commissioning standard for oil-fired appliances. It requires the engineer to complete a combustion analysis (CO₂%, CO ppm, flue gas temperature, efficiency), record the results on an OFTEC commissioning certificate, and hand it to the customer. Target combustion figures for a pressure-jet oil boiler: CO₂ 10–13%, CO <100ppm (preferably <50ppm), net flue gas temperature 150–250°C, combustion efficiency >85%.

Summary

Commissioning an oil-fired appliance correctly requires more than starting the boiler and checking for obvious faults. OFT105 commissioning involves systematic verification of combustion performance using a calibrated flue gas analyser, adjustment of the burner to achieve target combustion parameters, and formal documentation of the results. The commissioning record is the evidence that the boiler has been set up correctly and is operating safely and efficiently.

For OFTEC-registered engineers, combustion analysis at commissioning and annual service is a professional and regulatory requirement. An oil boiler commissioned without combustion analysis and a certificate is not OFTEC-compliant.

Key Facts

• OFT105 — the OFTEC commissioning category; engineers must hold OFT105 registration (or it must be included in their OFT101 scope) to legally issue commissioning certificates with combustion analysis
• Flue gas analyser — the instrument used to measure combustion products in the flue; measures CO₂ (or O₂), CO, flue gas temperature, and calculates combustion efficiency (using the Siegert method); must be calibrated annually; common brands: Kane, Testo, Flue Gas Pro
• CO₂ target — for a pressure-jet oil burner on kerosene: 10–13% CO₂ is the target range; below 10% indicates excess air (inefficient, cold flue, increased condensation risk); above 13% indicates insufficient combustion air (risk of CO production and sooting)
• CO target — carbon monoxide in the flue should be <100 ppm; ideally <50 ppm; above 100 ppm indicates incomplete combustion — adjust the air/fuel ratio; above 200 ppm requires the boiler to be taken out of service until the cause is identified and rectified
• Net flue gas temperature — flue gas temperature minus air temperature at the boiler intake; typical range 150–250°C for a non-condensing boiler; condensing oil boilers will show lower flue temperatures (below 60°C in condensing mode)
• Combustion efficiency — calculated from CO₂%, net flue gas temperature, and fuel type; typical target ≥85% for a non-condensing oil boiler; condensing boilers should achieve 90–94%
• Smoke number (Bacharach) — a test for unburned soot particles in the flue; performed by drawing a sample of flue gas through filter paper and comparing the resulting stain to a reference scale (0 = clean, 9 = very sooty); target ≤1 for domestic oil boilers
• Draft measurement — the draught over the burner (negative pressure differential between the combustion chamber and the flue); typically -0.1 to -0.2 mbar for most domestic oil boilers; too little draught causes combustion problems; too much wastes heat up the flue
• Burner adjustment — air settings on the oil burner (air band, air shutter) are adjusted to achieve target CO₂%; oil pressure is set per the manufacturer's specification for the nozzle size fitted; head position is set per burner installation guide
• OFTEC commissioning certificate — the formal record; issued via the OFTEC portal; includes: appliance details, combustion analysis results, smoke number, flue draught, oil pressure, nozzle size and type, engineer's OFTEC registration number; given to the customer and retained by OFTEC

Quick Reference Table: Target Combustion Parameters (Kerosene, Pressure-Jet Burner)

Detailed Guidance

Commissioning Sequence

Before starting the burner:

1. Inspect the heat exchanger and combustion chamber — no blockage, no debris, previous service date (if applicable)
2. Check the oil supply: filter condition, oil flow rate, no air in the supply line
3. Confirm nozzle size and type matches the manufacturer's specification for the appliance
4. Check electrode gap and position per burner manufacturer's setting data
5. Confirm flue connections are complete and unobstructed

First firing:

1. Purge air from the oil supply line (bleed screw on the pump or pre-purge on the controller)
2. Start the burner; observe ignition; confirm flame established within the lockout time
3. Allow the boiler to run for 5–10 minutes to reach stable operating temperature before taking measurements

Combustion analysis:

1. Insert the flue gas analyser probe into the flue sampling point (required on all oil appliances per Part J — a permanent sampling hole with a cap)
2. Allow the analyser to stabilise (typically 30–60 seconds)
3. Record CO₂%, CO (ppm), flue gas temperature, and calculated efficiency
4. Perform smoke test: insert the smoke pump probe into the sampling point; draw 10 strokes; compare filter paper to Bacharach scale; record result
5. If results are outside target, adjust the air band on the burner (small increments; stabilise for 30 seconds after each adjustment before re-measuring)

Final checks:

1. Confirm oil pressure at the pump is set per the manufacturer's nozzle/pressure specification (measured with a pressure gauge on the pump test port)
2. Measure flue draught (at the draught diverter or flue sampling point)
3. Confirm the boiler cycles correctly on thermostat demand
4. Check all controls (programmer, thermostat, cylinder thermostat) are operating correctly
5. Check for oil leaks at all connections
6. Record all results on the OFTEC commissioning certificate

Combustion Analysis Equipment

Flue gas analyser: A calibrated electrochemical cell analyser is required. The CO and CO₂ cells degrade over time and must be replaced and recalibrated according to the manufacturer's schedule (typically annually for CO cell; every 2 years for CO₂). An out-of-calibration analyser cannot be relied upon — results may indicate compliance when the appliance is actually producing unsafe CO levels.

Smoke pump (Bacharach pump): A hand pump drawing flue gas through a paper disc. The disc is compared against the Bacharach scale (0–9). Target ≤1 for a domestic oil boiler. Above 1 indicates incomplete combustion — black soot particles in the flue. Adjust the air supply.

Oil pressure gauge: A glycerine-filled pressure gauge with 0–20 bar range; connects to the pump test port via a flare-fit adaptor. Set oil pressure per the nozzle manufacturer's specification (typically 7–10 bar for domestic burners).

Issuing the Commissioning Certificate

After completing all commissioning checks, the certificate is issued via the OFTEC portal:

1. Log in to the OFTEC installer portal
2. Enter the property address, customer name, appliance details (make, model, serial number)
3. Enter combustion analysis results and other commissioning data
4. Submit — OFTEC records the certificate and generates a certificate number
5. Print or email a copy to the customer; retain a copy in your own records

The certificate number is the customer's proof of OFTEC-compliant commissioning. It is required by insurers, mortgage lenders, and solicitors on property sale.

Frequently Asked Questions

What if the CO reading is above 100 ppm and I cannot get it below by adjusting the air settings?

If CO remains above 100 ppm after air adjustment, the cause must be identified before the boiler is left in service. Common causes: blocked or scaled heat exchanger (preventing complete combustion), incorrect nozzle size or type, damaged electrodes causing poor ignition, oil supply contamination. Take the boiler out of service and advise the customer not to use it until the cause is rectified. Do not issue a commissioning certificate for an appliance with a CO reading above 100 ppm.

Does every oil boiler service require a commissioning certificate?

No — a commissioning certificate is issued for new installations and major appliance replacements. Annual servicing uses a separate OFTEC service record (not a commissioning certificate). However, combustion analysis must be performed and recorded at every annual service. If the boiler fails the service checks, an advisory notice must be issued (similar to a Gas Safe "At Risk" notice for gas).

The existing boiler has no flue sampling point. Can I still perform combustion analysis?

No — a permanent flue sampling point is required by Approved Document J for all oil-fired appliances. If the sampling point is missing (common on very old installations), it must be fitted before combustion analysis can be performed. Fit the sampling point as part of the service visit.

Regulations & Standards

• Building Regulations Approved Document J — requires a permanent flue sampling point on all oil-fired appliances; OFTEC commissioning and service requirements

• OFTEC OFT600 — technical standard for oil-fired appliance installation and commissioning; the reference document for OFT105 procedures

• BS EN 267 — oil burner standard; combustion performance requirements

• COSHH Regulations — handling of combustion analysis equipment and oil; relevant to flue gas exposure

• OFTEC — oftec.org — OFT105 commissioning requirements and portal

• OFTEC OFT600 — technical installation and commissioning standard

• Kane Instruments — kane.co.uk — flue gas analyser calibration and guidance

• oftec registration oft101 — OFTEC registration and scope of competence

• oil boiler service procedure — annual service procedure including combustion analysis

• building regs part j oil — Part J requirements for flue sampling points and commissioning