What is a combi boiler?
One unit that does heating and hot water on demand, with no cylinder or tanks. Excellent for most homes — not all.
A combi — short for combination — boiler heats your radiators and produces hot water on demand from a single unit. No hot water cylinder, no cold tank in the loft.
The advantages
- No cylinder or tanks, so you get the airing cupboard and loft space back
- Hot water on demand, with no waiting for a tank to reheat
- No heat lost from a cylinder standing hot all day
- Generally cheaper and quicker to install
Where a combi struggles
A combi heats water as it passes through, so its hot water output is limited by flow rate. Run two showers at once and both will suffer.
If your home has two or more bathrooms in regular simultaneous use, or your incoming mains pressure is poor, a system boiler with a cylinder is usually the better answer — even though a combi is the fashionable one.
Combi or system?
As a rough guide: one bathroom, good mains pressure, combi. Two or more bathrooms used at the same time, or weak mains, system boiler with an unvented cylinder.
The honest test is your water flow rate, which takes an engineer about two minutes to measure. Anyone quoting for a combi without checking it is guessing.
Want this priced for your property?
Send BPS Plumbing & Heating a few photos and the rough measurements and you'll get a written quote that sets out exactly what's included — so you can compare it properly against anything else you've been given.