Combi boilers are the most popular choice in UK homes, and for good reasons. They are not right for every house, though. Here is a balanced look at what they do well and where they fall short.
The advantages
Space. A combi heats water directly from the mains, so you do not need a hot water cylinder or a cold water tank in the loft. That frees up an airing cupboard and loft space.
Hot water on demand. There is no stored supply to run out. Turn on a tap and the boiler heats water as it flows.
Simpler system. Fewer parts, and mains-fed hot water at good pressure for showers and taps, if your supply is strong enough.
Often quicker to install. With less pipework and no tanks, a straightforward swap can be quick.
No standing heat loss. Because there is no stored hot water, no energy is lost keeping a cylinder warm.
The drawbacks
Flow is limited. A combi can only heat so much water at once. If two showers run together, or someone runs a bath while the dishwasher fills, the flow and temperature drop. Larger homes with several bathrooms usually do better with a system or regular boiler and a cylinder.
Reliant on mains pressure and flow. If your water supply is weak, a combi will struggle. Our guide to normal mains water pressure explains how to check.
Hard water. Limescale builds up in the heat exchanger. A scale-reduction measure or a water softener helps in hard water areas.
Hot water takes a moment to arrive. You may wait for the water to heat, and if the tap is a long way from the boiler, a bit longer.
Not ideal for some add-ons. Combis are not suited to systems that need a stored supply, for example certain solar thermal set-ups.
Who is a combi good for?
- Flats and smaller houses with one or two bathrooms
- Homes where space is tight
- Households with moderate hot water use
- Anyone with decent mains pressure
Who should think twice?
- Large families with several bathrooms in use at once
- Homes with weak mains water
- Properties where a cylinder is already in place and works well
Combis and the rules
In England, a new gas combi installation must include time and temperature controls and an additional energy-saving measure, under what is commonly known as Boiler Plus. We fit these as standard, and we will explain what is included in your quote.
Not sure which type suits your house? Read our guide to combi, system and regular boilers, or talk to us and we will survey your home and recommend the right one.
