The tests of 3 Heat Pumps (HP) from 3 European manufacturers were performed in controlled laboratory environment, over several days period each. Each HP implemented prototype control rules to modulate its power consumption proportionally to frequency and voltage instantaneous deviations. The outdoor unit is exposed to varying weather conditions-cold, average, and warm-while indoor unit aims to achieve different temperature settings to assess its performance in heating and cooling of a virtual building. The unit's electrical supply is controlled to replicate typical distribution grid conditions, as in system splits and low-voltage scenarios (load/generation imbalances). Voltage amplitude and frequency are monitored alongside thermal variables like thermal power and hydraulic circuit supply temperature to the virtual building. These experiments' showed that current HPs in the market implementing such control offer 1 %/s modulation speed of rated power, insufficient during fast frequency deviations, and feature several off-nominal modes (e.g., defrosting/oil gathering/ramp-up) during which active power modulation is impractical. Nonetheless, reaction speed's improvement areas clearly exist for products under development, gradual modulation of HP active power from local grid measurements is shown feasible and able to support grid in enhancing stability with negligible influence on user thermal services.