A hole in a pipe or polymeric casing associated with a district heating system is sealed by means of a polymeric patch that comprises a backing layer (2), a heat-activatable bonding layer (4) for securing the patch to the pipe or casing, and an electrically heatable layer (4). A further polymeric layer (8) may be included in the patch remote from the backing layer (2) when the substrate itself is not polymeric. The layers may be separate, or one layer may perform more than one function. Tooling (Figure 5) may also be provided to enhance the sealing of the hole when using the patch and method of the invention.
