Which type of combi boiler do I need?
Originally published 1 March 2019. Some figures have since changed - see our latest guides.
Finding the right combi boiler mainly depends on the size of your home and how much you are willing to spend in the short term. Combi boilers become more reliable as they go up in price, as you are paying for the durability of the equipment.
Which? has reported the average cost of a boiler repair at around £210, and that of the most reliable brands, 63% of boilers are likely to be fault-free after six and a half years, compared to only 45% of the least reliable. Two of the most trusted brands are Vaillant and Worcester Bosch, which is why BASI installs both.
What size combi boiler do I need?
The size of your boiler depends on the size of your property and how many bathrooms you have. By size we mean the wattage or power, not the physical shape. Because combi boilers generate hot water as needed, the power required depends on how many radiators, taps, baths and showers it serves, plus insulation and room sizes.
As a general rule of thumb:
| Type of home | Combi boiler required |
|---|---|
| 1-2 bedrooms, 1 bathroom | 18-24kW |
| 2-3 bedrooms, 2 bathrooms | 24-28kW |
| 3 bedrooms, 1 bathroom | 24-28kW |
| 3 bedrooms, 3 bathrooms | 30kW |
| 4 bedrooms, 1-2 bathrooms | 28-32kW |
| 4-5 bedrooms, 2-3 bathrooms | 30-32kW |
| 5+ bedrooms, 3 bathrooms | 30-40kW |
These are general calculations. The exact model varies with the size, age and insulation of your home, and how many people use hot water at the same time. Your installation engineer will assess all of these and recommend the right boiler.
Can I expect any guarantees?
Every good quality boiler comes with a guarantee. For premium models like Vaillant and Worcester Bosch, the manufacturer’s warranty lasts up to ten years, on the condition the boiler has an annual service. The boilers we install also come with two years’ cover on pipework, radiators and materials fitted as part of the installation.
If you would like help choosing the right combi boiler, our team is happy to advise, or read our guide on combi and system boilers.