What a hybrid is
A hybrid heating system has two heat sources: a heat pump, nearly always air source, and a boiler, usually the home's existing gas boiler or a new one. Both feed the same radiators. A controller decides which runs, or whether both run together, hour by hour.
There are two broad kinds. An add-on hybrid fits a heat pump to an existing boiler system, with a controller linking them. A packaged hybrid is designed as one product, with the heat pump and boiler sold and controlled together. Either way, the heat pump part works exactly like any other heat pump; see how heat pumps work.
How the controls decide
Different products use different rules, often in combination:
- Outdoor temperature. Below a set point, called the bivalent point, the boiler takes over or helps, because the heat pump's efficiency has fallen and the home's demand has risen.
- Demand. When the home needs heat fast, for example after a cold night, the boiler can boost.
- Price. Some controllers compare the cost of a unit of heat from each source, using the tariff and the heat pump's current efficiency, and run whichever is cheaper.
- Hot water. Some designs leave hot water to the boiler entirely.
The price rule is the same sum as on our cost page. At the price cap for 1 October to 31 December 2026, a heat pump achieving 2.8 makes heat at about 9.40p a kWh and a 90% gas boiler at about 8.86p, so a price-led controller would switch between them as conditions changed the heat pump's efficiency.
Which homes a hybrid can suit
- Homes where a heat pump alone would need many larger radiators or major insulation work the owner is not ready for.
- Homes with a relatively new boiler that the owner wants to keep using.
- Homes with no space for a cylinder, where the boiler keeps doing hot water.
A hybrid usually needs a smaller heat pump than a full system, because the boiler covers the coldest days. That can mean a smaller outdoor unit and fewer radiator changes.
What it does not do
A hybrid keeps a fossil-fuel boiler and a gas connection, so the home keeps paying the gas standing charge, 29.68p a day on the cap for 1 October to 31 December 2026, and keeps a boiler to service. And because the boiler covers the coldest, highest-demand days, a share of the heat still comes from gas.
Grants
GOV.UK says the Boiler Upgrade Scheme does not provide a grant for a hybrid heat pump system, such as a gas boiler with an air source heat pump, and it does not fund replacing an existing low carbon heating system. In Scotland, Home Energy Scotland's heat pump funding requires the heat pump to meet all of a home's heating and hot water, so hybrids, air-to-air and exhaust air heat pumps are not eligible there; its grant for qualifying heat pumps is up to £7,500. The Boiler Upgrade Scheme does contribute £2,500 towards an air-to-air heat pump in a home, which is a different kind of system.
Hybrid or heat pump alone?
The honest comparison is between a hybrid now and a full heat pump now, with the cost of each, the work each needs, and the grants each can or cannot get. A full system designed for the home usually needs more work at the start but no boiler. A hybrid needs less work now but keeps the boiler, the gas connection and the gas bill. Ask for both designs in writing if you are undecided.
Designing a hybrid well
The value of a hybrid depends on how much of the year the heat pump does the work. A design that hands over to the boiler too early, or a controller set to favour the boiler, can leave the heat pump idle most of the winter. The questions to ask are where the bivalent point is set and why, what rule the controller uses to choose between the two, whether hot water goes to the boiler or the heat pump, and roughly what share of the year's heat the heat pump is expected to supply.
Flow temperature matters here too. If the radiators need very hot water to keep the home warm, the heat pump's efficiency falls and the controller will hand over to the boiler more often. Some owners use a hybrid period to find out which rooms struggle at lower temperatures and upgrade those radiators, which is one way a hybrid can lead to a full heat pump later. The flow temperature guide explains the link between radiator size and water temperature.
Hybrids and hot water
Hot water is where hybrid designs differ most. Some keep a combi boiler and let it make all the hot water, so the heat pump only heats rooms and no cylinder is needed; that suits homes with no space for one. Others store hot water in a cylinder and heat it with whichever source the controller prefers. The first is simpler to fit; the second lets more of the year's heat come from the heat pump. Either way, the boiler still needs its annual service and a gas safety check, as any gas boiler does.
A hybrid shares the heating with a boiler, so it helps to know what a heat pump on its own could do: is my home suitable? covers that question, the running costs estimator gives a first idea of the bills, and types of heat pump compares the other designs.