Heating systems

A heating system comprising:

• a water heating system for heating potable water and/or a space heating system;
• a heat pump arranged to provide heat to the water heating system and/or a space heating system;
• a buffer vessel arranged between the heat pump and the water heating system or space heating system for storing fluid circulated by the heat pump;
• a buffer vessel heater for directly heating fluid in the buffer vessel;
• a controller configured to:
• control electric power from an electric power grid to the heat pump and the buffer vessel heater;
• detect a grid stress event;
• determine a heat pump energy penalty incurred in starting up the heat pump for providing heat in response to the grid stress event under a present operating condition;
• and,
• vary, in dependence on the determined heat pump energy penalty, a power provided to the buffer vessel heater.

A controller for a heating system comprising:

• a grid stress event detector for detecting a grid stress event;
• a data receiver for receiving sensor data;
• a processor configured to determine a heat pump energy penalty incurred in starting up the heat pump for providing heat in response to a grid stress event in dependence on received sensor data;
• and,
• a power control module configured to vary the power provided to an electric heating element in dependence on the heat pump energy penalty.