Buying advice

Best combi boiler 2026 — honest picks for each situation

There's no single "best" combi boiler — the right choice depends on your property, water hardness, budget, and how long you're staying. Here are our picks by category, based on fault-code data across 17,000+ boilers and what engineers actually recommend off the record.

Prices below include installation

Straight swap with no complications. Add 15–25% if you're moving the boiler position, converting from conventional to combi, or need new pipework. Quotes from Boxt, Heatable and iHeat are fixed-price and include VAT, installation, and parts.

Our picks by category

#1 Best overall

£2,400–£3,200 installed

Worcester Greenstar 4000

Hits the sweet spot: proven reliability, excellent customer support, widely-installed so parts are cheap and fast. 94% efficiency, A-rated, 10-year warranty with approved installer.

Best for: Most 3-bed semis with 1–2 bathrooms.

#2 Best value

£1,800–£2,600 installed

Ideal Logic Max

Comparable efficiency to Worcester at £400–£600 less. 10-year warranty. Logic+ (cheaper sibling) is solid too but Logic Max has the better modulation for mixed-use households.

Best for: Tight budgets, landlords, first-time buyers.

#3 Best premium

£2,900–£3,800 installed

Vaillant ecoTEC Exclusive

Stainless steel heat exchanger (premium build), whisper-quiet, 12-year warranty with Advance installer. The "forget about it for 15 years" option.

Best for: Homeowners staying put, hard-water areas, noise-sensitive (flats).

#4 Best for small flats

£1,500–£2,200 installed

Alpha E-Tec NX 25

Compact footprint, 25kW output (plenty for 1-bath flats), 10-year warranty. Fits in a kitchen cupboard more easily than bigger brands.

Best for: Flats, 1-bed houses, low hot-water demand.

#5 Best for big houses

£2,700–£3,600 installed

Viessmann Vitodens 100-W (35kW+)

German build quality, up to 98% efficiency, high-output for houses with 2+ bathrooms running simultaneously. Less common than the big three but very reliable.

Best for: 4-bed+ houses, two bathrooms used at once.

#6 Honest budget pick

£1,600–£2,300 installed

Baxi 800 Combi

British-made, 10-year warranty, solid reliability record. Not as efficient as top picks but saves £300+ on upfront cost.

Best for: Anyone who wants British-made without paying Worcester money.

What size combi do you need?

Property	Radiators	Output
Small flat	Up to 8	24–25 kW
2/3-bed, 1 bath	8–10	28–30 kW
3/4-bed, 1–2 bath	10–15	32–35 kW
4+ bed, 2+ bath	15+	38–42 kW