Which boiler have I got?

Checked against its sources: Updated 3 November 2026

To tell which boiler you have, look for a hot water cylinder, tanks in the loft, a pressure gauge, and the model name on the label on the boiler.¹ No cylinder and no tanks usually means a combi.²

Which boiler have I got?: key facts

A wall-hung boiler in a kitchen cupboard. AI-generated picture.

First clue	Cylinder or no cylinder²
Second clue	Tanks in the loft or not²
Third clue	Name and model on the label¹
Fuel clue	The label or range name; LPG and oil versions exist³
Records	Benchmark checklist, if your installer completed it⁴

Covers: Homes with a wet heating system, UK.
You: Look at the outside of the boiler, the airing cupboard and the loft hatch area if safe. Read labels and the manual.
A professional: Anything needing the case off. An engineer can confirm the type at a service.

1 The quick check

Work through these in order, without taking anything apart.

What you can see and what it usually means
What you find	Usually means	Why
No cylinder, no loft tanks	Combi boiler	Hot water heated on demand²
Cylinder, no loft tanks for the heating	System boiler	Cylinder without feed tanks²
Cylinder and loft tanks	Regular boiler on an open-vented system	Two tanks feed and top up²
Boiler behind a gas or electric fire in the chimney breast	Back boiler	Baxi's description²
No flue at all, and electrical connection only	Possibly an electric boiler	No flue to extract gases⁵

These are good clues and not a guarantee. Baxi's 600 Heat guide shows a heat-only boiler can sit on a sealed system too, so a boiler with a cylinder and no tanks is not always sold as a system boiler⁶.

2 Reading the label

The maker's name and model are usually on a label on or beneath the appliance, placed there for the user:

Worcester 4000: data label centrally on the bottom of the appliance, in line with the control panel¹.
Baxi 600 Heat: an information label under the boiler, showing model, serial number and Gas Council number⁶.
Main Eco Compact: model, serial number and Gas Council number on the information label, there for user reference⁷.
Vaillant ecoTEC plus: serial numbers on the data plate⁸.

The model name often says the type outright, as in Baxi 600 Combi 2, Baxi 600 Heat or Greenstar i System Compact. Baxi asks that the serial label is not removed or covered⁶. There is no need to take a case off to read any of this, and doing so is for an engineer only.

3 Condensing or not, and which fuel

A narrow plastic condensate pipe, and a plume at the flue at times, point to a condensing boiler². Natural gas is stated on some labels and guides, for instance Main says its boiler is factory set for natural gas⁷. A tank outside points to oil or LPG³.

4 If it is still unclear

The installer's paperwork helps, including any Benchmark record left with the boiler⁴. Otherwise, ask whoever services the boiler to write the type and system down for you. Knowing it matters because repressurising and many fault steps depend on the model.

Sources

Worcester Greenstar 4000 user manual 6720891170, p6, 2020/09, read 3 November 2026.
Baxi's heating glossary read 3 November 2026.
LPG boilers, Worcester Bosch read 3 November 2026.
Approved Document L for England, para 8.8, commissioning evidence read 3 November 2026.
Electric boilers, Viessmann UK read 3 November 2026.
Baxi 600 Heat user manual 7726861-01, pp10, 13, 20, 1/19, read 3 November 2026.
Main Eco Compact Combi user guide 7716571-04, p12, read 3 November 2026.
Vaillant ecoTEC plus operating instructions 0020308119_03, section 3.3, 28.11.2023, read 3 November 2026.