The three boiler types side by side
| Regular boiler | System boiler | Combi boiler | |
|---|---|---|---|
| Cold water tank in the loft | Yes | No | No |
| Hot water cylinder | Yes (vented) | Yes (usually unvented) | No |
| Where hot water pressure comes from | Gravity from the loft tank | Mains pressure | Mains pressure |
| Several taps at once | Good, if the cylinder is sized well | Good, if the cylinder is sized well | Limited by the boiler output and mains flow |
| Space needed | Most — loft and airing cupboard | Airing cupboard | Least — boiler only |
| Hot water when the stored supply runs out | Wait for the cylinder to reheat | Wait for the cylinder to reheat | Unlimited, one or two outlets at a time |
Why tanked systems still make sense
Combis are popular because they free up space and never run out of hot water, but they heat water on demand, so they can only supply so many outlets at once. In a home with two bathrooms where people shower at the same time, a stored cylinder can deliver more water to more taps simultaneously.
Low mains flow is the other reason. A combi can only be as good as the water coming into the house. If the flow at the kitchen tap is weak, a system with stored hot water often gives a better result than a combi would.
Regular boilers with loft tanks are common in older homes and suit properties with older pipework that might not cope with full mains pressure. They also keep a gravity supply if the mains is interrupted, for as long as the tank holds water.
How to tell what you have now
A quick look round the house usually settles it.
- A plastic or galvanised tank in the loft with a ball valve and pipes running down: you have a regular (open-vented) system.
- A copper cylinder in the airing cupboard with a smaller header tank alongside it in the loft: also a regular system.
- A cylinder with a pressure vessel and valves on it but nothing in the loft: likely a system boiler with an unvented cylinder.
- No cylinder and no loft tank, with hot water coming straight from the boiler: a combi.
Changing from a tank system
- Can I get rid of the tanks?
- Often, by switching to a combi or to a system boiler with an unvented cylinder. Removing the loft tank also removes the risk of it freezing or leaking. The decision depends on hot water demand and the mains flow, which is measured before recommending anything.
- Will my old pipes cope with mains pressure?
- Older systems were designed for gentle gravity pressure. Moving to mains pressure can expose weak joints, so the pipework is checked as part of planning the change.
Start by opening the loft hatch and the airing cupboard. What you find there tells you which boiler you have, and knowing how your household actually uses hot water tells you whether keeping a tank is still the right answer.