OFTEC Study Guide 2026

A fire valve is a fusible link valve installed on the oil supply line near the appliance. In a fire, the fusible link melts (typically at 68°C), closing the valve and cutting off the fuel supply to prevent the fire being fed.

Net flue gas temperature is calculated by subtracting the ambient room temperature from the measured flue gas temperature. This figure is used with the CO2 reading to calculate combustion efficiency and assess heat losses.

Pollution of controlled waters is a criminal offence. Penalties include unlimited fines and/or imprisonment. Additionally, the polluter can be liable for the full cost of clean-up operations, which can run to hundreds of thousands of pounds.

Excess air beyond what is needed for combustion absorbs heat as it passes through the boiler and carries that heat up the flue. While some excess air is necessary for safe combustion, too much wastes energy.

High O2 readings (above 6-7% for kerosene) indicate excessive air entering the combustion zone. This lowers CO2, reduces efficiency, and may cause flame instability. The air band or damper needs adjusting.

Condensing oil boilers are 10-15% more efficient than non-condensing models, meaning less fuel is burned to produce the same heat. This directly reduces CO2 emissions (by the same percentage) and lowers fuel costs for the householder.