A combi boiler produces hot water when a tap opens and normally heats radiators directly. A heat battery stores energy before demand. Replacing one with the other changes both the fuel path and how the home handles peaks.
The short answer
A combi can suit homes with adequate gas and water flow that value compact, on-demand hot water. A whole-home heat battery may suit a planned move from fossil fuel where the electrical supply, tariff and stored capacity cover the building's demand.
Hot-water behaviour
Both can avoid a conventional cylinder, but neither creates mains pressure. Compare delivered flow at winter inlet temperature and simultaneous outlets.
Space heating
The combi fires when rooms call for heat. A heat battery must contain enough energy and release enough power between charges. Require a heat-loss design for the latter.
Bills and standing charges
Do not compare the cheapest electricity period with the gas unit rate alone. Include efficiencies, peak top-ups, standing loss and whether removing the boiler also removes every other gas appliance.
Infrastructure and disruption
One path may need flue and gas work; the other may need a new high-load electrical circuit, controls and supply assessment. Compare complete installations.
Resilience
Both modern systems need electricity for controls and pumps. Ask what hot water and heating remain during a power cut or equipment fault.
Your next step
Give both designers the same hot-water pattern and room heat-loss figures. Reject a comparison that sizes one system and guesses the other.
Sources
Primary and independent references checked by our editorial team.
- Energy storage options explained — Energy Saving Trust Checked 10 Nov 2026