Work on fixed water and heating installations needs an autoriseret VVS-installatør (authorised plumbing contractor), or a firm that brings one. Ask which it is, and ask for that on the invoice (faktura). Authorisations are looked up at Sikkerhedsstyrelsen, sik.dk.
Helsingør and nearby North Zealand towns such as Hørsholm have older coastal houses and apartments near the station. Salt, wind and older roofs show up on roof and facade jobs. The same 2 businesses as the Danish page: Helsingør VVS Service ApS, Sylvest VVS A/S.