Profits generated by district heating systems when participating in ancillary service markets in the electricity sector are studied in this report. An hourly scheduling model is developed to optimally schedule district heating units to meet the heat demand, minimize costs and maximize revenues from electricity markets. The output is used to evaluate the additional profits made by participating in the existing Swedish ancillary markets in addition to the day-ahead electricity market. Case studies are run in two district heating systems, one in Nyköping and one in Gothenburg, for the historical years of 2021 and 2022. Nyköping’s system is also used to evaluate potential profits from ancillary service markets in future scenarios for 2025, 2035 and 2045. Finally, Nyköping’s system is used to evaluate potential additional profits generated by two investments that enhance the flexibility that can be provided to the electricity sector: better CHP ramp rates and larger thermal storage. The analysis of the results shows, for both historical and future years, that participating in ancillary services brings about additional profits. These vary depending on the year, studied district heating system. Profits from electricity markets are shown to increase by up to 40% in Nyköping and 200% in Gothenburg when looking at the historical years. Doubling the CHP ramp rates ability for delivering ancillary services or doubling the size of the heat storage are shown to result in up to another 6% of additional profits. In the future scenarios, profits from electricity markets are shown to increase by up to 94%.