Two identical eddy correlation systems were operated to determine the fluxes of heat, water vapour, and carbon dioxide over a meadow. A new error source of heat flux measurements by sonic anemometers has been identified and corrected for: sound transit times were altered regularly by liquid water forming and evaporating on the sonotrodes. Concerning the gas fluctuation measurements using closed-path analysers, several errors are treated, including an empirical approach to correct for unknown sorption effects in the tube line. The measured fluxes are investigated with respect to energy balance closure and source areas. It is shown that good closure alone does not guarantee representativeness of fluxes. However, considering changes in surrounding vegetation yields consistent energy budgets.