Key checks
When to call an engineer
If the problem involves fixed wiring, high-current heating equipment, repeated tripping, unvented hot water or uncertainty about the supply arrangement, testing is safer and usually faster than swapping parts.
Related specialist pages
Why “number of radiators” is not enough
Radiator count is a rough clue, not a heat-loss calculation. Two homes with the same number of radiators can have very different heat demand because of floor area, insulation, glazing, exposed walls, ceiling height and desired internal temperature.
Electrical supply is part of the sizing decision
An electric boiler's kW output becomes a significant electrical load. The incoming supply, phase arrangement, other large loads and diversity all need to be considered. A boiler that suits the heat loss may still require electrical work before it can be safely connected.
Hot water can be a separate design problem
Heat-only and system electric boilers normally need a hot-water cylinder if they are to provide domestic hot water. The cylinder size and reheat strategy depend on occupancy and usage, not just boiler output.
Reviewed 9 September 2026 · NICEIC-registered electrical work · G3 unvented hot-water qualified · Dimplex Pro / Quantum installer training.