Typical prices
A like-for-like vented cylinder swap is the cheapest option. Upgrading from a vented system (with a loft tank) to an unvented cylinder costs more but can improve water pressure dramatically.
| Job | Typical cost |
|---|---|
| Vented cylinder, like-for-like | £900 – £1,500 |
| Unvented cylinder, like-for-like | £1,400 – £2,500 |
| Vented to unvented upgrade | £1,800 – £3,000 |
| Heat-pump-ready cylinder | £1,800 – £3,500 |
| Replacement immersion heater only | £150 – £300 |
Indicative costs to replace a hot water cylinder (2026, supplied and fitted)
Vented vs unvented
Vented cylinders are fed by a cold water tank in the loft and rely on gravity, so water pressure is often low. Unvented cylinders are fed directly from the mains, giving better pressure, but they must be installed by an engineer qualified for unvented systems (often called G3) and serviced annually.
Signs it's time to replace
Most cylinders last 15–25 years. Leaks from the cylinder body can't usually be repaired.
- Leaks or damp patches around the cylinder
- Rust or corrosion on the cylinder or connections
- Hot water taking much longer to heat
- Running out of hot water more quickly
- Discoloured or rusty hot water
- Old, poorly insulated cylinders
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Choosing a size
Cylinder size depends on your household's hot water use. A 120–150 litre cylinder is typical for a smaller household; 180–250 litres may suit larger families with multiple bathrooms.
Should you switch to a combi?
If you have a small household and one bathroom, switching to a combi can free up the airing cupboard. Larger households often keep a cylinder for better flow to multiple taps. See replacing a conventional boiler with a combi. Get quotes from local heating engineers.
