For most flats, terraces and three-bed semis a combi is the right answer — hot water on demand, no cylinder, no tanks. Two or more bathrooms showering at the same time points to a system boiler with a cylinder instead. Older heat-only setups usually convert to a combi when they reach the end of their life, from £2,699. Count your bathrooms and let the survey confirm the rest.
Combi
A combi heats water on demand — no cylinder, no tanks, one appliance doing everything. It is the right answer for most flats, terraces and three-bed semis, which is why the fitted prices on this site are combi prices. Instant hot water, space back in the airing cupboard and loft, and nothing stored going cold.
System boiler
A system boiler heats a hot water cylinder, so several outlets can draw strong hot water at once. That is its whole case: if you have two or more bathrooms and a household that showers at the same time, a combi is often the wrong answer, and a system boiler with a cylinder usually is the right one. We price system-boiler jobs at the survey rather than from a table, because the cylinder side varies house to house.
Heat-only (open vent)
The older arrangement — a boiler, a cylinder, and feed tanks in the loft. Plenty of Birmingham homes still run one, and they can run for years. But when one reaches the end, most households convert to a combi rather than fit like-for-like: for most three-bed houses it is the change that makes the biggest difference to running costs and loft space. That job is a conversion, from £2,699.
The honest rule
The best boiler does not exist in the abstract — only the right output for the radiators you have and the right warranty for the years you intend to stay. Count your bathrooms, be honest about simultaneous showers, and let the survey confirm the rest — flue route, gas supply and water pressure included.