Combi boiler guides & advice

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

Getting started

Guide

What is a Combi Boiler?

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

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Combi vs System vs Regular

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

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Choosing a New Combi Boiler

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

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Sizing & Energy Efficiency

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

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Installation & optimisation

Guide

Installation Best Practice

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

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Reduce Flow Temperature

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

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Commissioning Checklist

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

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Reading Combi Datasheets

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

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Common problems

Homeowner

Boiler Pressure & Topping Up

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

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Hot Water Problems

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

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Boiler manuals by brand

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

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