Choosing a new boiler isn't just about the brand. The type of boiler, its output and how it's installed make a bigger difference to how well your heating and hot water work. This guide explains the three main types and how to decide between them.
Combi boiler
Best forFlats and homes with one bathroom
- Hot water on demand, straight from the mains
- No cylinder or loft tanks, so it saves space
- Flow drops if two showers run at once
System boiler
Best forHomes with two or more bathrooms
- Stored hot water for several taps at once
- Strong mains-pressure showers
- Needs a cupboard for the cylinder
Regular boiler
Best forOlder homes with low mains pressure
- Works with your existing tanks and cylinder
- Simple like-for-like replacement
- Tanks use loft space, and pressure is lower
Combi boilers
A combination boiler heats water directly from the mains when you turn on a tap, and heats your radiators. There's no hot water cylinder and no tanks in the loft, which saves space.
- Good for: flats and homes with one bathroom, and homes where space is tight.
- Watch out for: running two showers at once. A combi can only heat so much water at a time, so flow drops if several outlets are on.
- Needs: decent mains water pressure and flow. We test this before recommending one.
System boilers
A system boiler heats your radiators and a hot water cylinder, which stores hot water ready to use. Most modern systems use an unvented cylinder fed at mains pressure, which gives strong showers throughout the house.
- Good for: homes with two or more bathrooms, and households that use a lot of hot water at once.
- Watch out for: the cylinder needs a cupboard, and once the stored hot water is used up it takes time to reheat.
- Also: a cylinder can be paired with other heat sources in future, such as solar thermal or a heat pump.
Regular (heat-only) boilers
A regular boiler works with a cold water tank and an expansion tank in the loft, plus a hot water cylinder. It's the traditional set-up in many older UK homes.
- Good for: homes with low mains pressure, or where replacing the whole system isn't practical right now.
- Watch out for: lower water pressure unless a pump is added, and tanks taking up loft space.
Many homeowners with a regular system switch to a combi or system boiler when they replace it. It frees up the loft and usually improves pressure, but it's a bigger job, so we'll price the options side by side.
What size boiler do you need?
Bigger isn't better. For a combi, the output mainly affects how quickly it can heat running water, so it's sized for your hot water demand. For system and regular boilers, the output should match the heat your home loses on a cold day. An oversized boiler switches on and off more often, which wastes gas and adds wear. We size boilers properly at survey rather than guessing from the number of bedrooms.
What a good installation includes
- Cleaning the existing system and adding inhibitor
- A magnetic system filter
- Heating controls that meet current Building Regulations
- A correctly routed flue and condensate pipe, protected against freezing
- Commissioning, a completed Benchmark checklist and warranty registration
- Notification to Building Control by the Gas Safe registered installer
Warranty length varies by manufacturer and model, and most warranties require an annual service by a Gas Safe registered engineer. Ask exactly what's covered and for how long.
Next steps
Tell us about your home and current system, and we'll recommend the right type and size, with a fixed price. Get a boiler quote.
Keep reading
Landlord safety certificates explained
Gas safety records, EICRs and alarms: what the law requires, how often, and the deadlines that catch landlords out.
Read the guide
EICR codes explained
What each observation code on an EICR means, what makes a report unsatisfactory, and what to do about it.
Read the guide