With Ray Lewington in charge for the 2002–03 season, Heiðar showed a marked improvement. Although still prone to injury (he did not start the season until late September), he finished the season Watford's top goal scorer with 13, including goals in Watford's run to the FA Cup semi-Finals. In 2003–04 injury kept Heiðar out of most of the first half of the season. On his return he put in some notable performances, the most notable being his leading of the line against Chelsea in the FA Cup.