A company named "Which?" took a poll of 3,000 boiler owners in 2010 to find the most reliable boiler. According to the poll results reported on This Is Money, Vaillant is one of the top two most reliable boiler brands. The poll states that only 29 percent of owners of Vaillant boilers experienced any problems with the boiler, and this was the lowest percentage of problems reported of any brand.
Furnace Compare rated Viessmann boilers at number 19 on its poll of customer satisfaction ratings. Only 34 percent of users recommended them, and almost 50 percent reported being very unsatisfied. Unsatisfied customers complained about parts breaking and systems failing.
Although Vaillant boilers were rated number 2 on the list, only two customers actually reviewed the brand on the Furnace Compare poll. One problem with these findings is that Furnace Compare is based out of the United States, and the Vaillant brand is primarily available only in the United Kingdom and Europe.
The "Which?" company is a consumer-product-rating service located in the UK. Its poll found Vaillant boilers most reliable, and the next-most reliable brand is the Worcester, with only 32 percent of the owners reporting problems. This Is Money did not mention Viessman boilers as part of the "Which?" poll results.
The best combination-boiler overall on the "Which?" poll is a gas-powered Baxi model: This combination boiler both heats the water and the house.