Heat Only vs System Boiler: Which One Should You Choose?

If you’re replacing your boiler or planning a heating upgrade, you might be choosing between a heat only boiler and a system boiler. Both are great options for homes that need plenty of hot water—but how do they differ, and which one’s right for your household?

Let’s take a closer look at how each boiler works, what they’re best suited for, and what to consider when making your decision.

What Is a Heat Only Boiler?

A heat only boiler, often called a regular or conventional boiler, is one of the oldest and most familiar types of boiler found in UK homes. It works with two separate tanks and a hot water cylinder:

  • A cold water tank, usually stored in the loft

  • A feed and expansion tank to maintain system pressure

  • A hot water cylinder to store the heated water

Cold water flows down from the loft tank into the boiler, where it’s heated. This hot water is then stored in the cylinder and sent to your taps or radiators when needed.

Benefits of Heat Only Boilers

  • Great for larger homes with more than one bathroom

  • Can handle multiple hot water demands at once

  • Works well in areas with low mains water pressure

  • Compatible with older pipework and radiators

  • Can be connected to solar thermal panels to save energy

  • Still gives access to hot water even if the boiler breaks (thanks to the stored supply)

Things to Be Aware Of

  • Requires extra space for the loft tanks and hot water cylinder

  • Slightly less energy efficient due to heat loss from stored water

  • Installation can be more complicated and time-consuming

What Is a System Boiler?

A system boiler is a more modern version of a heat only boiler. It also requires a hot water cylinder, but it takes cold water directly from the mains, so there’s no need for loft tanks. The boiler itself contains the pump and expansion vessel, making installation easier and more streamlined—especially in newer homes.

Advantages of System Boilers

  • No cold water tank needed in the loft

  • High-pressure hot water from the mains

  • Faster and more efficient hot water delivery

  • Takes up less space than a heat only system

  • Easier to install in modern properties or new builds

What to Consider

  • Still needs a hot water cylinder, so not as compact as a combi boiler

  • May not be suitable for homes with older pipework

  • Not ideal for properties with very limited space

What’s the Difference Between a Heat Only and a System Boiler?

The biggest difference is how the system is set up. A heat only boiler relies on loft tanks and gravity to feed water into the system, while a system boiler connects directly to the mains. This means a system boiler typically delivers better water pressure and takes up less room.

A heat only boiler is often better for older homes or where water pressure is low. A system boiler is ideal for newer homes where space-saving and high-pressure hot water are priorities.

Which Boiler Type Is Best for You?

A Heat Only Boiler May Be Right If:

  • You live in an older property with traditional pipework

  • Your home has two or more bathrooms

  • You have space in the loft for tanks

  • Your mains water pressure is low

  • You want a system that continues working (to some extent) during repairs

A System Boiler May Be Best If:

  • You want to get rid of your loft tanks

  • Your home is modern with up-to-date pipework

  • You want better water pressure at taps and showers

  • You need a space-saving solution

  • You want quicker, more efficient hot water delivery

What’s the Cost of Installing One?

Installation prices for both heat only and system boilers are generally similar. A full supply and installation—including the new boiler, labour, and any pipework adjustments—typically ranges from £1,400 to £4,000, depending on your home’s current setup and the complexity of the job.

At Thermo-Tec Plumbing and Heating, we offer clear pricing, expert advice, and full installation services across Reading, Wokingham, Earley, Woodley, Shinfield, Barkham and nearby areas.

Still Not Sure Which Boiler You Need?

If you're unsure whether a heat only or system boiler is the best fit for your home, we’re here to help. Our experienced team can assess your setup, talk through your heating needs, and recommend the right solution.

Contact Thermo-Tec Plumbing and Heating

Call us today on 07850 116944

We’re a local, family-run heating and plumbing company offering reliable service and expert advice to homes throughout Berkshire. Let us help you find the ideal boiler for comfort, performance, and long-term value.