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.
Once you have compared the layouts, explore system boiler installation or regular boiler replacement for planning the work in your home.
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.
Which suits a home with several bathrooms: a system or regular boiler?
Both can supply stored hot water, so the cylinder capacity, reheat performance and simultaneous demand matter as much as the boiler type. A system boiler with a suitable unvented cylinder can provide mains-fed hot water where the incoming supply supports it. A regular boiler may still suit an existing tank-fed arrangement. Assess the whole setup rather than choosing by bathroom count alone.
Can a regular boiler be swapped for a system boiler?
Often, but it is a conversion rather than just an appliance exchange. The installer needs to assess the existing pipework for sealed operation, the cylinder arrangement and the changes to tanks, valves and controls. Agree what can remain and what needs changing during the survey.
Do system and regular boilers both need a cylinder?
For stored domestic hot water, both work with a separate hot water cylinder. Neither supplies instantaneous tap hot water in the way a combi does. The cylinder type and associated tanks depend on the installation, so changing boiler type does not by itself decide every hot water component.