The best boilers for 2021

Here’s how you pick a boiler that suits your home and your wallet. 

Engineer installs a combi gas boiler

Boilers aren’t the most exciting things to buy. But they’re an important and necessary purchase. An inefficient boiler might mean that you pay more than you need for your energy bills. 

There are a few types of boilers available. Depending on what kind of house you have, you might have limited options. 

So, it pays to take the time to find a boiler that suits you.

Here’s a rundown of the different types of boiler and our top picks in each category. The boiler's we'll be looking at here are all condensing boilers.

Get personalised electricity deals straight to your inbox

Get switch ready


What’s a condensing boiler?

A condensing boiler is an energy-efficient boiler that recovers heat energy from waste gases.

By law, all new and replacement boilers must be condensing boilers. An A-rated condensing boiler runs at 92-94% efficiency. An old, non-condensing boiler runs at about 70% efficiency.

You can tell whether you have a condensing boiler by looking at the flue. The flue is pipe that carries the boiler’s exhaust outside the house.

If the flue is metal and you can’t see any steam coming from it when the boiler’s on, you’ve likely got a non-condensing boiler.

Replacing your gas boiler with a condensing boiler could make your central heating run better. This reduces emissions and shaves some money off your energy bill.


What are the different types of boiler?

There are three main kinds of condensing boiler. These are:

  • Combination (combi) boilers
  • Conventional heat-only boilers
  • Sealed system boilers.


What are combi boilers?

Combi boilers provide heat and hot water direct from the boiler itself. There's no need for an external water tank.

If you live in a small place, a combi boiler could be a good bet for you.

Since you get your heat and hot water on demand, there’s less wasted energy. This makes it the boiler of choice for eco-conscious folks.

Combi boilers tend to be less of a hassle to install. So, getting one fitted shouldn’t be as expensive as with other types.

The downside with combi boilers is that they don’t work so well in larger homes or areas with low water pressure.


What are the best combi boilers?

Industry experts Heatable's top recommended combi boilers are from Worcester Bosch. Their best seller - the Worcester Bosch Greenstar 30i - is said to be a great all-rounder for reliability and with a good warranty. The Greenstar 30i is compatible with both LPG and solar heating systems.

You can expect to pay just over £1,000 for a Greenstar 30i.

Other models of note:

The Viessmann Vitodens 050-W, which has excellent scores for reliability and performance. This costs less than the Greenstar, at around £800.

The Valliant ecoTEC plus - an energy-efficient combi boiler that doesn’t skimp on performance. This’ll set you back in the region of £1,200.

These boilers come with a standard manufacturer warranty of about five years. Depending on who you go with for your boiler, they could extend that to up to 10 years.


What are conventional boilers?

Heat-only gas boilers take up a bit more space than a combi boiler, so a bigger house is necessary.

These boilers have two tanks:

  • A hot water tank (usually stored in an airing cupboard)
  • A cold water tank (usually in the attic).

A conventional boiler might suit you if:

  • You’ve more than one bathroom
  • You need hot water in lots of places at once.

The downside is that it could be a bit more expensive to install as there’s more equipment involved.

And if you want to jump in a hot bath right this instant, tough luck. You may need to wait for the water tank to heat up first.

These drawbacks have led to a fall in popularity for conventional boilers in favour of the combi.

According to The Eco Experts, a conventional boiler could cost in the region of £1,500 - £2,500.


What are sealed system boilers?

Sealed system boilers are like heat-only boilers – the main difference is that they don’t have a cold water tank.

This could be a useful feature if you have a loft conversion and space is an issue. Also, these boilers are pressurised, so could in handy if you live in an area with low water pressure.

The trade-off with these boilers is that they tend to be on the pricey side. And, as with conventional boilers, you’ll need some extra space to fit the hot water tank.

According to Heatable, a sealed system boiler is likely to set you back between £1,895 and £2,345.


What are my options if I don’t have access to gas?

If you live in a rural area, you may not have access to the gas grid to get one of these boilers. It’s estimated that over four million properties don’t have access to gas.

An option for you could be an oil-fired boiler.

The main difference between these and gas boilers is that you’ll need a separate storage tank for the oil.

There are oil-fired boilers available that are as efficient as their gas counterparts. The downside is that it might cost a bit more to install the storage tank.

Also, it’s generally thought that oil isn’t as environmentally friendly as gas.


How powerful should my boiler be?

When comparing boiler models, you’ll notice that they vary in power, depending on your needs.

A qualified engineer should be able to tell you how powerful your boiler should be.

But to get a ballpark figure, count your radiators:

  • If you’ve got fewer than 10 radiators, then a 27kW boiler or under should work. This likely means you’re in a one or two-bedroom property with one bathroom.
  • If you’ve got 10-15 radiators, then aim for a 28-34kW boiler. These cover three-bedroom terraced and semi-detached properties with up to two bathrooms.
  • Anything over 15, go for 35kW or over. This is for those with four or more bedrooms and more than two bathrooms.


Can I get a grant to help pay for a new boiler?

There are some schemes available that could help you reduce the cost of a replacement boiler.

The Energy Company Obligation (ECO) is a government-backed energy scheme that works with energy suppliers to reduce energy costs.

Whether you’re eligible depends on:

  • Where you live
  • Your supplier
  • Your personal circumstances.

Ask your energy supplier about the ECO scheme, or check out this advice from Ofgem.


Can I get a heat pump instead of a boiler?

The government is working toward becoming a zero-emissions country by 2050. Part of this involves looking at how we heat our homes.

Nothing has been written into law, but it’s thought that a ban on gas boilers in new homes may come in the next few years. An alternative to using a boiler is a heat pump. 

Heat pumps come in two flavours:

  • Air source heat pumps (ASHP). These extract heat from the air outside and use pumps to heat it before going into your central heating.
  • Ground source heat pumps (GSHP). These extract heat from water in pipes underground.

These systems run on a small amount of electricity instead of using mains gas. You can even run them using solar energy, so you could have truly renewable heating.

The initial cost of installing a heat pump can be quite large. The Energy Saving Trust estimates it costs £9,000 and £11,000 to put in an AHSP.

Thinking about going for a heat pump? You’ll need to balance out the initial cost with any potential savings you’d get in future.

Is your gas boiler already efficient, with an A rating or above? The Energy Saving Trust says it could work out to be more expensive to install a heat pump.


Can I use solar power to heat my boiler?

Yes, you can!

Solar collectors attached to your roof connect straight to the boiler to heat the water.

If you’re eco-conscious, this is one way to help lower your carbon footprint. If you’re budget conscious, it’s a way of reducing your energy bills.

There are a few things to consider, though:

  • Do you have roof space that gets enough sunlight?
  • Do you have space for a separate hot water storage tank?
  • Is your boiler compatible with solar heating?

A solar heating system costs between £4,000 and £5,000. It’s a big expense with long-term investment benefits.

READ MORE: Green energy explained


Smart technology for boilers

Some boilers may come with some kind of smart technology to help you manage your energy usage.

On the one hand there are digital thermostats. These let you micromanage the temperature of your central heating.

This works in your favour. Turning your thermostat down by one degree could shave £80 off your heating costs.

On the other hand, you can also get smart radiator valves that let you control the heating in each room via your phone.

This degree of control over how and when you heat your home could save you a pretty penny on your energy bills.

These smart devices sometimes come with real-time diagnostic information. This lets you troubleshoot problems with ease.

If you’re replacing your boiler anyway, you might be able to get a deal on some smart tech while you’re there. 

READ MORE: How to make your home more energy efficient