Combi vs system vs heat-only boilers, explained plainly

The three types in one line each

• Combi — heats water on demand, no cylinder, no tanks. One box does everything.
• System — heats a stored cylinder of hot water, but takes its water supply straight from the mains. No loft tanks.
• Heat-only (conventional/regular) — the traditional setup: boiler, cylinder, and feed tanks in the loft.

Which suits your home

One bathroom and limited space points to a combi. Two or more bathrooms used at the same time points to a system boiler with a cylinder. A heat-only boiler usually only makes sense as a like-for-like replacement where the tanks and cylinder are staying, or where the mains pressure is too weak for anything else.

The hot water truth

A combi's hot water is limited by its flow rate — one great shower, two mediocre ones. A cylinder stores hot water, so several outlets can run at once until it empties. That single fact decides more boiler choices than any efficiency figure.

What we stock

Our shop carries all three types: over 400 combi packs, plus system and heat-only packs from the same ten brands. Fitted, we quote combi and system installations — the boiler builder asks about your bathrooms and cylinders, then recommends the type rather than guessing.