A charged heat battery contains thermal energy, but releasing it can depend on powered controls, pumps and valves. The answer during a power cut is product- and system-specific.
The short answer
Ask whether the system can deliver taps or space heat with the grid off and for how long. Do not assume a thermal battery provides electrical backup or that a home battery automatically keeps the heating circuit live.
Hot water
A mains-pressure, through-flow arrangement may still need an electrically controlled valve or pump. Gravity and vented systems behave differently. The manual should state the safe outage condition.
Space heating
Wet central heating usually needs circulation pumps and controls. Stored heat without circulation may remain unavailable to radiators.
Home battery integration
An electrical battery needs backup equipment and protected circuits to operate when isolated from the grid. The heating system's starting current and sustained load must fit that design.
Return of power
Check whether the heat battery resumes its schedule, charges immediately or needs a manual reset. A full-power restart alongside EV charging and other loads can affect maximum demand.
Freeze and fault protection
Products installed in garages, lofts or outbuildings may have temperature requirements during long outages. Follow the siting manual.
Your next step
Ask for a written outage sequence covering a charged unit, a depleted unit and restoration of power. Keep manual isolation instructions accessible without an app.
Sources
Primary and independent references checked by our editorial team.
- Energy storage options explained — Energy Saving Trust Checked 10 Nov 2026