Flue temperature can be monitored and used as an indication of efficient boiler operation. A 50C rise in flue temperature indicates a one per cent efficiency loss.5 The optimum temperature can be obtained by reading the flue temperature immediately after the boiler has been serviced and cleaned. Preventative maintenance should include flue temperature readings at least three times a day, at the same firing rate and comparing this temperature with the optimum.

A temperature variation may indicate the need for boiler cleaning. The fuel source used by the boiler will affect the degree of fouling. For example, low grade fuels such as coal and wood will cause more fouling than natural gas.

Soot is usually removed with a brush and vacuum. Fire side tubes can build up scale on the water side which can be difficult to remove, requiring mechanical or acid cleaning, so prevention by good water treatment is essential.

Electronic combustion efficiency testers with data loggers can be used for increased monitoring. Inline temperature sensors must be regularly calibrated and checked for fouling.