Combi boiler guides & advice

Clear, practical help on combination boilers — from choosing and sizing to installation, efficiency, and everyday troubleshooting.

Getting started

Definition, how combination boilers work, and the pros and cons compared with system and regular boilers.

Which boiler type suits your home — space, hot-water demand, and mains supply.

Controls, filters, installation best practice, and recommended products before you buy.

Match kW to heat loss and hot-water demand; modulating output and running-cost savings.

Pipework layout with de-aerator, dirt separator, bypass, limescale protection, and flushing.

Lower heating flow temperature to save gas, improve reliability, and stay in condensing mode.

Gas rates, combustion, bypass, inhibitor, DHW checks, and handover documentation.

DHW flow at ΔT, heating vs hot-water kW, modulation, and mains flow testing.

Normal pressure range, using the filling loop safely, and when to call an engineer.

No hot water, weak shower, lukewarm taps — typical combi causes and safe checks.

Free user and service manuals for leading UK manufacturers at BoilerManuals.com.

Vaillant Worcester Bosch Ideal Baxi Potterton Glow-Worm Viessmann Intergas Alpha British Gas

Visit MyBoiler.com for in-depth articles, tools, and heating resources — or browse free manuals at BoilerManuals.com.