Boiler types explained

• combi boilers
• system boilers
• heat-only boilers

Combi boilers don’t use a hot water cylinder – all the heat and hot water comes directly from the boiler itself. This makes them a good option if you don’t have much space, and they’re often the least expensive kind of boiler.

Combi boilers give you heat and hot water on demand, making them a more efficient choice for smaller households. Combi boilers may be less suitable for:

• Houses with multiple bathrooms or higher hot water demands. The ‘on demand’ feature of a combi boiler works less well when you need hot water in multiple places at once.
• Houses with low water pressure.

System boilers have a separate water cylinder to store hot water. They’re more efficient than combi boilers at producing hot water, but heat is lost from the hot water cylinder over time.

Being able to store hot water makes system boilers a good choice for larger families with higher hot water needs. This is because you can draw hot water from the storage tank to multiple taps at the same time.

Also, having a hot water cylinder lets you store energy from solar panels.

Heat-only boilers, also called regular or conventional boilers, work in a similar way to system boilers. The main difference is that heat-only boilers have two extra header tanks to store cold water, usually installed in the loft if there is one.

These kinds of boilers tend to suit larger properties or where you have low water pressure. The drawbacks with heat-only boilers are:

• you’ll need extra space to fit two extra tanks
• your hot water pressure may end up a lot lower than your cold water pressure

Heat-only boilers are unlikely to be suitable for a flat, as the header tanks need to be higher than the highest hot tap or radiator.

Most boilers in England, Scotland and Wales are gas boilers. These connect to the gas grid to provide fuel for your boiler when you need it.

If you have a mains gas connection, a modern, condensing gas boiler is usually the cheapest to run compared to oil, electricity, LPG and house coal.

In Northern Ireland, more than two-thirds of homes use oil boilers. These have a storage tank that needs refilling every few months. You may be able to save money by joining an oil buying club to get a discount. For more information, visit Consumer Council.

For homes that aren’t connected to the gas grid, LPG boilers are another option. Like oil boilers, you’ll need to refill your LPG tank periodically, depending on how much you use.

LPG is the most expensive of the three fuel types, but it has less CO2 emissions compared to oil.

There are several things to consider when deciding what type of heating system is right for you:

How much hot water you use

Large families using lots of hot water are likely to be better off with a system boiler. Smaller households using less hot water may be better off with a combi boiler.

How much space is available

Combi boilers don’t need hot water cylinders, and therefore need less space.

Compatibility with solar water heating

Solar water heating is easier to work with system boilers, although you can adapt combi boilers too.

Being heat pump ready

Most heat pumps work with a hot water cylinder. So, if you switch to a combi boiler now, you may need to put a cylinder back in if you want a heat pump in future.

The costs for replacing a boiler will vary, but a straightforward gas boiler replacement plus thermostatic radiator valves will typically cost about £3,700.

We recommend getting at least three quotes from different installers to ensure you get the best value for money. Look for installers that are certified by TrustMark, which is a government-endorsed quality scheme.

For gas and LPG boilers, the installer must be Gas Safe registered. Your installer will ensure your system complies with current building regulations and will make sure you get all the documentation to prove this. Keep these documents safe as you’ll need them when you sell the property.

Eventually, most homes in the UK will replace their fossil fuel boilers with more renewable alternatives. If you’re thinking about replacing or upgrading your boiler, now’s a good time to think about switching to a low carbon heating system.

These low carbon heating systems will lower your CO2 emissions and could also reduce your energy costs. How much you could save depends on the type of system and fuel you’re replacing.

Heat pumps

Heat pumps are one of the most efficient heating systems available. They’re powered by electricity and are more than three times more efficient than gas boilers

Solar water heating

Solar water heating uses energy from the sun to heat water in a hot water cylinder. Since the amount of sunlight varies throughout the year, solar water heating won’t give you 100% of your hot water needs. It’s best used alongside your boiler or an immersion heater, to make up the difference.