System Boiler or Regular (Heat-Only) Boiler
Both feed a hot water cylinder, but a system boiler is sealed and pumped with its own expansion vessel while a regular boiler relies on a feed-and-expansion tank in the loft.
Both feed a hot water cylinder, but a system boiler is sealed and pumped with its own expansion vessel while a regular boiler relies on a feed-and-expansion tank in the loft. The right one depends on what's already up there and what you're willing to change.
The case for a system boiler
No loft tanks to maintain, consistent sealed pressure, and a cleaner installation where the loft is being converted or insulated heavily.
The case for a regular boiler
Where the existing pipework is fragile microbore or the loft tanks are in good order, keeping the open-vented arrangement avoids disturbing a system that already works.
Which wins when
New build or full refurbishment favours system boilers almost every time. A straight like-for-like swap on an untouched older system often favours staying regular, at least until other work forces a change.
Talk through your loft and pipework
Describe your loft tanks and existing pipework and we'll tell you honestly which boiler type suits the building as it stands.
Questions we get asked
Is a system boiler simply a newer version of a regular boiler?
No, they're different arrangements rather than one replacing the other. Some homes are genuinely better served by keeping tanks.
Can I fit a system boiler onto existing gravity pipework?
Sometimes, after a pressure test and often a flush, but old joints that have never seen sealed pressure can reveal weak points once pressurised.
Does losing the loft tanks free up much space?
Usually a worthwhile amount, though it's rarely the main reason to choose — the pipework and cylinder decision matters more.