How does a boiler work? A boiler heats your home by turning cold water into hot water or steam, which is then pumped through your radiators or taps.
Simple enough. But there are different types of boilers, and they don’t all work the same way.
So, if you’re asking yourself, ‘how does a boiler work?’ Let’s break it down.
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The Basics
All boilers do three things:
- Take in cold water from the mains or a tank
- Heat it using a burner (usually gas, oil, or electric)
- Send it to taps and radiators through pipes
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Some boilers heat water as you use it. Others store hot water in a tank. That’s the key difference.
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How a Combi Boiler Works
Most UK homes now use combi boilers.
Here’s how they work:
- No storage tank needed
- Cold water comes straight from the mains
- It’s instantly heated by the boiler’s burner when you turn on a tap
- Hot water is sent directly to your taps or shower
- At the same time, it heats water for your radiators
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Everything happens on demand. You only heat what you use.
Combi = Compact + Efficient. Perfect for smaller homes with one bathroom.
How a System Boiler Works
System boilers are better for homes with higher hot water demand.
They use:
- A hot water cylinder (usually in an airing cupboard)
- No need for a cold water tank in the loft
- Cold water comes from the mains
- The boiler heats it and stores it in the cylinder
- You get hot water from the tank when needed
This setup lets you run multiple taps at once, but once the cylinder runs out, you have to wait for it to reheat.
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How a Regular (Conventional) Boiler Works
These are more common in older UK homes.
They need:
- A cold water tank (in the loft)
- A hot water cylinder (in the airing cupboard)
- More space overall
- Water from the cold tank is fed into the boiler
- Boiler heats the water
- Hot water is stored in the cylinder
- Central heating and taps are fed from this tank
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It’s less efficient but can work well in homes with very old pipework or low water pressure.
What Powers a Boiler?
Most UK boilers use natural gas. Others may run on:
- LPG (liquefied petroleum gas)
- Oil
- Electricity
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The boiler burns fuel in a combustion chamber, heats a metal exchanger, and transfers that heat to water. Simple mechanism, effective results.
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What Controls It?
Modern boilers have smart thermostats, timers, and weather sensors. You can:
- Set schedules
- Control room temperature
- Monitor usage
- Control everything from your phone
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This helps reduce energy waste and cut bills.
Need a New Boiler or Upgrade?
FAQs - How does a boiler work?
Combi gives instant hot water without a tank. System uses a hot water cylinder for storage.
Usually yes, but it depends on pipework and pressure. We assess it during your survey.
On average, 10–15 years with proper servicing.
Not always. A combi boiler heats both through the same system.
Modern A-rated condensing boilers (especially combi types) are the most energy-efficient.
You can turn off heating, but keep it on for hot water—especially with a combi boiler.
Find out how much a new boiler will cost
Simply fill in the quick form below and we’ll give you an instant estimate.
