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How Do Boilers Work?

Even though every home has a boiler, few people know how they work. But, this is a disadvantage if something goes wrong and you don’t know what has happened, or how to fix it. Learning about boilers can also be handy when you are wanting a new boiler installation – you will be able to know what type you want and what price range you will be looking at. This is why we thought we’d share some of our knowledge and give you the basics.

Ultimately, your boiler is what sends hot water through your pipes, into radiators and through your taps. They are therefore necessary for a warm house and hot water.  This is the basis for all boilers, but the way that they work and the different elements they are made up of differ.

Conventional or Heat-only Boilers

This is the traditional way that heating is provided in all homes before the 1970s. It is made up of a cold-water tank and a hot water cylinder. This is where the water is stored.

When your hot water is needed, you turn the thermostat on, turning on the boiler sending water to a pump. This then travels to a 3-port valve which tells the water where to go – either for hot water or heating. It then goes to either the radiator or the to tap and then back into the boiler in a constant circuit.

The water comes from a tank in the loft; there is one tank for cold water and one for hot.

These conventional boilers can be fitted with an immersion heater as a back-up. This way, if there is not enough hot water, or your boiler has broken down and in need of a boiler repair, more can be heated and used. However, it does take time for the heater to warm up, which may cause an inconvenience.

Because the system needs two tanks, it can be problematic if in a smaller home, as the tanks take up valuable space.

System Boilers

These work the same as a conventional boiler but saves space because all the parts of a conventional boiler are inside the system, making installation quicker and easier. This is also because there is no need for a separate cold-water tank. Not needing two different tanks saves storage space. Water is heated and stored in a tank, which is usually in the airing cupboard.

Water in this cylinder can be sent to many different sources, so you can use sinks, baths or showers at the same time. This makes system boilers ideal for larger homes.

You are able to set timers for system boilers, so you can choose when you want to use the hot water. Like conventional boilers, if you need extra hot water, it takes time to reheat the tank.

Combi Boilers

Instead of having a heating system with a big tank, and an indirection boiler or a heating element inside, the combi boiler heats the water used to heat the house and the water used for washing at the same time.  It does this because there are two independent cylindrical heat exchanges – one linking to the radiators and one connecting to the hot-water supply.

The system contains a plate heat exchanger. This has a high heat recovery so it transfers heat from one body of water to another very quickly.  Cold water from cylinders enters the plate heat exchanger in pipes that run amongst each other and heats up. The two different sources do not mix.

When you turn on the tap or its time for your central heating to be on, the boiler burns gas, causing the heat exchanger to heat up, heating either water from the water cylinder, or the one for central heating.

A benefit of using combi boilers is that you don’t have to heat up large amounts of water. Most system boiler tanks use 100L of water that store both. Combi boilers only use 35L.

Another advantage is that combi boilers do not have time to warm up. This means that unlike conventional or system boilers, you can have hot water instantly.


Give us a call for a free quote or advice.

Now that you know more about how the different types of boilers work, you can decide which type is right for you. So, if you are looking for a new boiler in Bournemouth call us today – At Senior Heating and Plumbing, we have a range of Viessman boilers . We also carry out boiler repairs and boiler services around Poole and Bournemouth, so give us a call for a free quote or advice.

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