Low availability of sustainable biomass prevents transition of district heating in Europe away from fossil fuels. The need for sustainable fuels stems from current energy generation structure, which mainly relies on centralised combined heat and power operated as baseload units. Our study shows that districts with generation of renewable power, heat and synthetic natural gas can reach complete energy system decarbonisation even without biomass, only using wind and solar power as primary energy. It requires rethinking of interactions between electricity, gas and heating networks and a polygeneration solution with power-to-heat and power-to-gas technologies to fully utilise local solar and wind power and cover peak demands. Power-to-heat as baseload units supported with power-to-gas for seasonal and back-up energy storage are proposed as novel district heating approach. The operation of such polygeneration is tested successfully using a model of a Finnish district. Carbon dioxide circulation is analysed together with capacity requirements to synthetic natural gas and needed wind power installation. Resulting complete decarbonisation requires coordination and flexible operation of power-to-heat and power-to-gas capacity together with gas-fired combined heat and power plants and heat-only boilers, which ensures that renewable power production, heating and power needs, security of supply and grid limitations are met.