Jargon Buster - B

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Movement of the fluid from a downstream to upstream within an installation contrary to the intended direction of flow.

Balanced Flue appliance

Room sealed appliance which draws its combustion air from a point adjacent to the point at which the combustion products are discharged, the inlet and outlet being so disposed that wind effects are substantially balanced.


A valve for controlling the flow of water into a cistern, the valve being operated by the vertical movement of a float.

Banging sounds

This can be caused by overheating due to a variety of reasons, a build-up of scale due to hard water, a faulty boiler thermostat, a lack of water in the system or the pump not working.

Bleed valve

Used to release air that has gradually built up inside the radiator, preventing the panel from heating properly. If this does happen, check out our simple instructions on how to bleed your radiator.


An obstruction that could apply to a pipe or airway in a domestic appliance or central heating system.

Blocked Chimney

Can prevent boiler waste products being safely taken outside of the building. Mechanical defects and debris can also cause blockages.


A boiler is an appliance in which water or other fluid is heated. The fluid is then circulated out of the boiler for use in heating applications. Faulty boilers should only be dealt with by a Gas Safe Registered engineer.

Boiler flue

Passage for conveying combustion products to outside air.

Boiler flue thermostat

Heating system safety and control feature on a boiler that measures the temperature of gases entering the flue after the burner.

Boiler-energy manager/optimiser

A device that collects temperature data from sensors inside and outside the building, allowing the boiler to work at maximum fuel efficiency.


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