If you’re planning a bathroom upgrade, swapping taps, or dreaming of a rainfall shower, there’s one question worth answering first: what type of boiler do you have?
Different types of boilers deliver very different water pressure levels. And that directly affects what you showers, taps and heating you can install.
In this guide, we’ll walk you through the three main boiler types found in UK homes, explain how they impact water pressure, and help you figure out which one is quietly powering your daily routine.
The three main types of boiler in UK homes
Most homes will have one of the following:
- Gravity (conventional) boiler
- Combination (combi) boiler
- Unvented cylinder system (often referred to as a Megaflo system)
While they all heat your home and hot water, they differ significantly in how they store, heat and distribute that water, especially when it comes to pressure.
Let’s take them one by one.
Gravity boilers (conventional systems)
Gravity boilers are one of the older and more traditional systems you’ll find across the UK.
These systems usually include:
- A cold water tank in the loft
- A hot water cylinder in an airing cupboard below
Gravity systems typically deliver around 0.1 - 0.2 bar of pressure. As a rule of thumb, every metre of vertical drop creates roughly 0.1 bar of pressure. In most homes, that’s a 1 - 2 metre drop from loft to cylinder, hence the lower pressure output.
In practical terms? The flow is gentler. You’ll need to choose taps and showers designed for low-pressure systems to get the best performance.
You’re more likely to see gravity systems in:
- Older properties
- Period homes
- Houses that haven’t had a recent heating system upgrade
They heat stored water to at least 60°C to maintain hygiene and prevent bacteria build-up.
If your home has a tank in the loft and a cylinder in the airing cupboard, gravity is the likely answer.
Combination boilers (combi boilers)
The combi boiler is now the most common boiler type in UK homes. Unlike gravity systems, combi boilers:
- Don’t store hot water
- Heat water directly from the mains
- Activate only when you turn on a hot tap
There’s no loft tank and no separate hot water cylinder. Everything is compact and typically wall-mounted.
Combi boilers usually provide 1.0–1.5 bar, depending entirely on your incoming mains supply.
That delivers a noticeably stronger flow than gravity systems, but there’s a catch. Because hot water is heated on demand, pressure can dip if multiple taps or showers are used at the same time.
Combi boilers have become popular because they are space-saving, energy efficient and generally safe for drinking from any tap.
If your boiler fires up the moment you turn on the hot water - and there’s no tank in the loft - you likely have a combi.
Unvented cylinder systems (often called Megaflo systems)
Unvented systems are powerful, high-pressure setups designed for homes that demand more from their water supply.
The name “Megaflo” comes from Heatrae Sadia, whose Megaflo range helped popularise the design, but many manufacturers now offer similar systems.
Unvented systems include:
- A hot water cylinder
- A smaller expansion vessel
- No cold-water storage tank
Water is supplied directly from the mains and stored under pressure. As it heats and expands, the expansion vessel accommodates the increase in volume.
These systems typically deliver 3 - 5 bar of pressure, significantly higher than gravity or combi boilers. Ultimately delivering stronger showers, consistent flow across multiple outlets and greater flexibility when choosing taps and fittings.
Because of their size and performance, these systems are most common in large new build homes, properties with multiple bathrooms and homes with higher water demands.
How to tell which boiler you have
Not sure what’s working behind the scenes? Here’s a quick checklist.
Do you have an airing cupboard with a large cylinder?
If yes, you likely have either:
- A gravity system
- An unvented cylinder system
Is there a water tank in the loft?
A loft tank strongly suggests a gravity boiler. Combi systems don’t need one, and unvented cylinders rarely sit in lofts.
Does the boiler fire up when you turn on the hot tap?
If it fires up instantly then you likely have a combi. Doesn't respond quickly? Probably a gravity system. And if it stores hot water and reheats automatically, then its likely unvented.
Why your boiler type matters
Understanding your boiler type isn’t just helpful trivia. It directly affects:
- The taps and showers you can install
- Whether you need pumps or pressure-boosting solutions
- Bathroom renovation decisions
- Heating system upgrades
Choosing fittings that match your system and water pressure ensures better performance, improved efficiency and fewer frustrations later.
And that’s the kind of warmth we like! The reliable kind.
So, what it boils down to...
Your boiler quietly shapes your daily comfort. From the strength of your morning shower to how confidently you can run multiple outlets at once, it all starts there.
Once you know what system you have, you can make smarter choices, whether you’re refreshing a bathroom, upgrading your heating or planning something bigger.
And if you ever need a little guidance along the way, we’re always here for a chat. Heating might be technical, but it doesn’t have to feel complicated.
