Which type of combi boiler do I need?

‘Which combi boiler do I need?’

It’s a question we get asked a lot. Finding the right combi boiler mainly depends on the size of your home and how much you’re willing to spend in the short term.

Combi boilers, like almost anything in life, become more reliable as they go up in price, as you are paying for the durability of the equipment. If you have the money, then it’s much better to invest in a more reliable model.

According to Which? the average cost of a boiler repair is £210. The same survey revealed that, of the most reliable brands, 63% of boilers are likely to be fault-free after six-and-a-half years. This compares to only 45% of the least reliable models.

Two of the most trusted brands are:

  1. Vaillant
  2. Worcester Bosch

At BASI, we install boilers from Vaillant and Worcester Bosch. They’re two of the leading manufacturers, who consistently rank amongst the best-performing boiler brands. We selected these manufacturers because it’s important our customers get longevity from their new boiler.


‘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. When we say size, this is not simply referring to the physical shape of your system, but the wattage or power of the boiler.

Because combi boilers generate hot water as needed, the power required to keep them running efficiently depends on how many rooms they are serving. The more radiators, taps, baths and showers there are to fuel, the harder your boiler has to work.

In addition to the number of bathrooms and bedrooms your home has, the level of insulation and the size of the rooms will also be a factor.

As a general rule of thumb, these are the different size combi boilers you might need:

Type of home Combi boiler required
1-2 bedrooms, 1 bathroom 18-24kW
2-3 bedrooms, 2 bathrooms 20-18kW
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 and the exact model will vary depending on the size and age of your home, plus how well insulated it is. It’s also worth considering how many people live in your home, as this may mean people using different hot water supplies simultaneously.

Your boiler installation engineer will be able to asses all of these factors and provide you with an exact recommendation for the type of boiler you require.

‘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 for ten years. The only stipulation is that your boiler has an annual service to keep it in good working condition. Most reputable heating installers will send you a reminder when your service is due.

In addition to the boiler warranty, all of the boilers we install come with two years’ cover on all of the pipework, radiators and materials that come as part of the installation. This means you’re never left in the lurch if any unexpected issues occur once your boiler’s been fitted.

If you have any questions, please don’t hesitate to contact us on 0800 980 6018 or via [email protected].

Would you like to arrange a new boiler survey? Book an appointment today by calling or booking below.

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