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Biomass combined heat and power plants (CHPPs) can operate target-specifically because of their controllability while supporting decarbonization in district heating. The transition from the German Renewable Energies Act funding, which has promoted biomass CHPPs but is now about to expire, to direct marketing, is a major economic challenge for many biomass-heating grids. To successfully accomplish it, the flexible operation of biomass CHPPs, compared to the previous baseline-operation, is becoming an increasingly important requirement if participation in the electricity markets is to remain profitable. This paper presents a techno-economic assessment of flexible CHPP operation in a modeled district heating system with a CHPP, a peak load boiler and a thermal heat storage. The simulation model compares two cases - a natural gas and a wood-chip gasifier CHPP. The analysis of the results investigates the parameters that need to be adapted to make biomass-fired CHPP heating grids more efficient compared to fossil-fired CHPP heating grids in a flexible operating scenario. It highlights the technical and economic superiority of a fossil-fired CHPP in flexible operation in comparison to the wood gasifier system. The introduction of a CO 2 -tax on natural gas as a fuel, currently under discussion in Germany, would increase the competitiveness of the wood gasifier. • Simulation model of a district heating system. • Model units are wood or natural CHP plant, peakload boiler and heat storage. • Three scenarios for CHP plant dispatch under consideration of electricity prices. • Focus on dynamic differences of the CHP plant operation strategy. • Results show limitations in operational flexibility of the wood gas CHP plant. [ABSTRACT FROM AUTHOR]