Heating system and method for controlling a heating system

A method for controlling a heating system including

• a flow circuit arranged and configured to carry a flow of a working fluid at a set flow temperature to a heat emitting section in order to perform heating of a space;
• an electricity driven heat pump having a first heat exchanger connected to the flow circuit to transfer heat to the working fluid;
• a fuel fired boiler having a second heat exchanger connected to the flow circuit to transfer heat to the working fluid downstream of the first heat exchanger;
• the method comprising:
• determining a coefficient of performance (COPSet Flow Temperature) of the heat pump for the set flow temperature;
• determining a break even coefficient of performance (BECOP), the BECOP being an electricity price divided by a fuel price multiplied by a thermal efficiency of the boiler
• comparing the COPSet Flow Temperature with the BECOP;
• and
• if the COPSet Flow Temperature is smaller than the BECOP in a first hybrid mode
• determining an intermediate flow temperature at which the COPIntermediate Flow Temperature is higher than the BECOP,
• operating the heat pump so that the working fluid is heated to the intermediate flow temperature by the first heat exchange, and
• operating the boiler so that the working fluid is heated from the intermediate flow temperature to the set flow temperature by the second heat exchanger.