Guide
Combi vs system boiler
The honest comparison — including when a combi is the wrong answer.
Combi wins
Install cost
Combi is cheaper to fit; a system boiler adds the cylinder and pipework.
System wins
Hot water at once
System boilers keep pressure up when two showers run together.
Combi wins
Space
Combi needs no cylinder or tanks at all.
System wins
Solar / heat pump ready
A cylinder lets you add solar thermal or a heat pump later.
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