Grant Oil Boilers Vortex 21 Outdoor HE Combi Oil Boiler, External High Efficiency Combi Boiler, ERP Compliant Oil-Fired Boiler

Domestic boilers heat water for radiators or underfloor heating, and in many homes for the taps as well. This category covers gas condensing combi, system and heat-only boilers in a range of outputs, boiler and flue packs, separate flue kits and extensions, and some oil boiler flue parts.

Combi, system or heat only

• Combi: a compact boiler that heats water on demand straight from the mains, so no hot water cylinder or loft tank is needed.
• System: works with a hot water cylinder to store hot water but does not need a cold water tank in the loft.
• Heat only (regular): found on traditional systems with both a hot water cylinder and a cold water storage tank.

Check which type the home has now before choosing, as each suits a different arrangement of cylinder and tanks.

Output, flues and efficiency

Output is given in kilowatts; ask the installer to confirm the size the home needs. Check whether a boiler comes with a flue or as boiler only, and whether the flue needs to run horizontally through a wall or vertically through a roof. In England, Approved Document L sets a minimum seasonal efficiency of 92% (ErP) for gas boilers on wet central heating systems in homes.

Installation and safety

Work on gas pipework, appliances and their gas parts must only be carried out by a Gas Safe registered engineer. Oil boilers should be installed and commissioned by an OFTEC registered technician. The installer should complete the commissioning checklist and notify the work under the Building Regulations, either through a competent person scheme or to building control.

For filters, flue parts and fitting kits, see domestic boiler accessories; for thermostats and programmers, see heating controls.