The level of aftercare your retrofit measures will need depends on the contract you have with builders and the guarantees you’ve been given.
Normally, retrofit contracts include a ‘rectification period’ to deal with ‘latent defects’ and this varies from 3 to 12 months following installation. Remember to include this defects period requirement at tender stage as it might affect the price that contractors quote.
Guarantees from suppliers and manufacturers are longer: usually 5 years for boilers and 15-30 years for external wall insulation systems and roofs. Remember to check terms and conditions and remind your contractor that they may need to fill out and submit forms to qualify.