If you’re planning a new boiler installation or replacing an old unit, you’ve probably come across three main options: combi, system, and regular (conventional) boilers. Each type works differently and suits different homes, lifestyles, and budgets.

At AGM Plumbing & Heating, we install all three types for households across Oxfordshire. In this guide, we’ll explain how each system works, compare their pros and cons, and help you decide which boiler type is best for your home.

What Is a Combi Boiler?

A combi boiler (combination boiler) is a compact, all-in-one unit that provides both central heating and hot water directly from the mains supply. It heats water on demand, so there’s no need for a hot water cylinder or cold-water storage tanks.

How it works:
When you turn on a hot tap or your heating, the boiler fires up and heats water instantly. There’s no stored hot water – everything is produced as and when you need it.

Size and installation:
Combi boilers are compact (often small enough to fit in a kitchen cupboard) and require less pipework than other systems. Installation is usually quicker and less disruptive, provided your mains water pressure is good.

Combi Boilers: Pros & Cons

Advantages

• Extremely space-efficient – no cylinder or loft tanks
• Instant hot water
• Lower installation costs
• High energy efficiency with minimal heat loss
• Ideal for smaller homes and flats

Disadvantages

• Performance depends on mains water pressure
• Struggles with multiple taps or showers running at once
• Not ideal for large families or homes with several bathrooms
• If the boiler fails, you lose heating and hot water

Best for:
Flats, smaller homes, couples or single occupants, and properties with good mains water pressure.

What Is a System Boiler?

A system boiler works with a separate hot water cylinder but doesn’t need tanks in the loft. Many key components are built into the boiler itself, creating a sealed and efficient system.

How it works:
The boiler heats water and stores it in a cylinder. Hot water is supplied from this stored supply, allowing multiple outlets to run at the same time with good pressure.

Size and installation:
The boiler itself is compact, but you’ll need space for a hot water cylinder (usually in an airing cupboard). Installation is more involved than a combi boiler but simpler and cleaner than a conventional system.

System Boilers: Pros & Cons

Advantages

• Excellent hot water pressure
• Handles multiple bathrooms at once
• No loft tanks required
• More reliable for families with high usage
• You still have some stored hot water if the boiler fails

Disadvantages

• Requires space for a hot water cylinder
• Higher installation cost than combi boilers
• Some heat loss from stored hot water
• Cylinder requires occasional maintenance

Best for:
Larger homes, families, and properties with multiple bathrooms where loft space is limited.

What Is a Regular (Conventional) Boiler?

A regular boiler (also known as heat-only or conventional) is the traditional setup found in many older UK homes. It works with both a hot water cylinder and cold-water storage tanks in the loft.

How it works:
Water is stored in a tank in the loft, heated by the boiler, and then stored in a hot water cylinder until needed. An expansion tank manages pressure changes.

Size and installation:
This system requires the most space: a boiler, a hot water cylinder, and two loft tanks. Installation and maintenance are more complex.

Regular Boilers: Pros & Cons

Advantages

• Good water pressure for multiple outlets
• Suitable for very high hot water demand
• Often cheaper to replace like-for-like
• Familiar setup in older properties

Disadvantages

• Requires significant space
• Less energy-efficient
• More complex installation and pipework
• Higher heat loss and running costs
• Rarely the best option for modern homes

Best for:
Older properties where the system is already in place and changing to another type would be expensive or impractical.

Head-to-Head Comparison

How to Decide: Key Questions

How many people live in your home?
Singles and couples usually suit combi boilers. Families benefit from system boilers.

How many bathrooms?
One bathroom = combi works well.
Two or more bathrooms = system boiler recommended.

What’s your water pressure like?
Low pressure makes combi boilers unsuitable.

How much space do you have?
Limited space = combi
Space for cylinder, not loft tanks = system
Existing tanks in loft = regular may make sense

What’s your current system?
Sticking with your existing type reduces conversion costs.

What’s your budget?
Combi boilers are usually the cheapest to install. System boilers cost more upfront but suit busy households better long-term.

Our Recommendation

At AGM Plumbing & Heating, we find that combi and system boilers cover the needs of most modern homes.

• Smaller homes and flats: Combi boiler
• Larger homes with multiple bathrooms: System boiler
• Conventional boilers: Only recommended where replacing like-for-like makes sense

We are Gas Safe registered and Worcester Accredited Installers, which means we can offer extended guarantees of up to 12 years on selected Worcester Bosch boilers.

Get Professional Advice

Choosing the right boiler isn’t just about the type – it depends on your home’s layout, water pressure, usage habits, and future plans.

We offer free, no-obligation home surveys across Oxfordshire. Our engineers will assess your property and recommend the most suitable boiler system and model. We also provide flexible finance options from 2–10 years, including 0% interest-free plans.

We serve:
Oxford, Abingdon, Didcot, Witney, Woodstock, Kidlington, Bicester, and Wallingford.

Ready to find out which boiler is right for your home?
Get an instant quote today – it takes less than 30 seconds.