# Combi, system or conventional boiler?

Understand the storage layout before asking an engineer about suitability.

Updated 2026-11-10. Also on the [web page](https://boilerpros.fyi/guides/combi-system-conventional-boilers).

These names describe heating and hot water layouts. They do not by themselves specify output, fuel, installation cost or suitability for a home. Ask an engineer to assess the existing system and your hot water use.

## Combi

Worcester Bosch describes a combination boiler as a water heater and central heating boiler in a compact unit. It heats water from the mains when a tap opens. The layout does not need a separate hot water storage cylinder or cold water tank in the roof space. [Worcester Bosch, checked 2026-11-10.]

Ask the engineer to assess the incoming water supply and simultaneous demand. Explain which taps and showers you use together. Do not select a boiler only from a product's headline output.

## System

A system boiler uses a hot water storage cylinder. Worcester Bosch says the main heating and hot water components are built into the boiler and that a loft tank is not needed for this layout. [Worcester Bosch, checked 2026-11-10.]

Ask where the cylinder will stand, how hot water will be controlled and what work the existing pipework needs. Include cylinder and control work in the quote so you can compare it with a combi proposal fairly.

## Conventional or regular

Worcester Bosch uses regular, traditional, conventional and heat-only for the same broad boiler type. Its explanation describes a separate hot water cylinder and cold water storage tank in the loft, with a feed and expansion tank for the heating circuit. [Worcester Bosch, checked 2026-11-10.]

Existing tanks do not prove that the original layout remains in use. Ask the engineer to inspect it. Do not climb into an unsafe loft or move pipework to identify a system.

## What to send with a quote request

Send photographs of accessible equipment, your existing paperwork and a description of hot water problems. State whether you want to keep or remove a cylinder and whether space is a constraint. Ask the engineer to explain any recommendation in terms of your property.

Our boiler type selector compares storage definitions only. It does not calculate heat loss, water flow or appliance size. A system design requires an assessment. Do not use a category result as an instruction to alter gas or heating equipment.

## Sources

All sources below were fetched on 2026-11-10. This is the date checked, not a claim about the publication date. Recheck current terms before booking.

- [Worcester Bosch, Boilers explained](https://www.worcester-bosch.co.uk/products/boilers/explained), checked 2026-11-10.

## Questions

### Does a combi boiler need a separate hot water cylinder?

Worcester Bosch describes combi boilers as heating mains water on demand without a separate cylinder.