Overview
Worcester Bosch and Vaillant are consistently rated as the UK's two most reliable boiler brands. Both are excellent — the difference between them is marginal.
Reliability
Independent surveys show Worcester Bosch has a fractionally better UK reliability record. Both brands far outperform budget alternatives.
Warranty
Worcester Bosch: up to 12 years with accredited installer. Vaillant: up to 10 years. Worcester wins on warranty length.
Efficiency
Both brands achieve 94–96% efficiency at the top of their ranges. Effectively equal.
Price
Similar pricing across equivalent models — typically within £50–£100 of each other.
Parts availability
Worcester Bosch has a slight edge with the largest UK spare parts network of any boiler brand.
Verdict
Both are outstanding choices. Worcester Bosch edges it for the longer warranty and parts availability. Vaillant is preferred by some engineers for its engineering quality at the upper end of the range.