Central Heating Systems Explained: Types, Components And Upgrades

A combi heats water on demand with no storage, so there’s no cylinder taking up cupboard space, but it can struggle if two outlets run hot water at once. A system boiler heats and stores water in a cylinder, handling higher simultaneous demand better but taking up more space and needing the stored water to reheat once used.

In most cases yes, though it depends on your incoming mains water pressure and flow rate, which we’d check before recommending it. Some older properties with poor mains pressure are better suited to a system boiler with an unvented cylinder instead.

A well-maintained boiler typically lasts 12–15 years, though the wider system (radiators, pipework) often lasts considerably longer if it’s been looked after and not left to sludge up.

For larger properties, zoning (so upstairs and downstairs, or different areas, can be controlled independently) can noticeably improve comfort and reduce wasted heating in unused rooms. For a small flat it’s rarely worth the added complexity.

Yes to some extent — a combi avoids the standing heat loss of a stored cylinder, but a well-insulated cylinder with a system boiler isn’t far behind. Boiler efficiency and how well the system is controlled matter more than the basic type in most cases.

Usually a radiator or two can be added without an upgrade, but it’s worth checking the boiler has enough spare capacity first, particularly if you’re extending the property significantly.

This is one of the bigger jobs we do — it means running gas supply if it isn’t already there, installing a boiler, and fitting a full network of pipework and radiators throughout. Worth a proper survey rather than a phone estimate given how much this varies by property.

A boiler swap alone is usually a one-day job. A full system replacement including new radiators and pipework is more disruptive, typically several days, though we work room by room to keep at least some heating and hot water running where possible.

No — combi systems don’t use a cylinder at all, which is one of their main appeals in smaller properties where storage space is limited.

It can, particularly if the old pipework is narrower than modern standards or carries years of debris that a new, more efficient boiler is more sensitive to. It’s not automatically a problem, but when installing a new boiler onto an older system, a powerflush beforehand is usually worth the modest extra cost to protect the new appliance.

A telltale sign is if certain rooms have always struggled to reach a comfortable temperature even when everything works correctly, rather than only during a fault. A proper heat-loss calculation, which we can carry out during a survey, confirms whether the boiler and radiators were sized correctly or whether that’s been an underlying limitation since installation.