What is a heat exchanger in a boiler?
A heat exchanger transfers energy from one system to another without the need for contact. As water passes through the boiler pipes, the burner creates hot flue gasses which warm the surface of the pipe. Due to the high amount of stress experienced by heat exchangers, they’re commonly made of either aluminium or stainless steel.
The heat exchanger forms the beating heart of any boiler. As such, understanding how it works is important to keep your home warm and full of hot water.
What Types of Boilers Use Heat Exchangers
All household boilers are heat exchange boilers. This is because it’s a more efficient way to heat water than simply combining hot and cold water, or by using an open flame. However, certain boiler types will contain a different amount of heat exchangers or feature a different configuration.
Condensing boilers
Condensing boilers use the warm air and pipe heating method described above. In addition, the boiler has a ‘condensing’ area with a secondary heat exchanger that collects and disposes of water droplets. These form when warm air passes over pipes containing water that’s returning from radiators. This creates greater heat efficiency, as condensing boilers can recover as much heat as possible before it leaves the system.
Non-condensing boilers
Unlike condensing boilers, non-condensing boilers only feature a single heat exchanger. This, combined with their shorter pipe coil, causes non-condensing boilers to have a large carbon footprint. Due to their lesser efficiency, non-condensing boilers will typically release flue waste at higher temperatures (200°C or more).
The UK government requires all newly built boilers be condensing. So non-condensing types will only be found in older properties (pre 2005).
Combi boilers
Combination boilers usually contain two heat exchangers, one for central heating and one for creating hot water. The primary heat exchanger oversees the heating of radiator water. This travels to and from the boiler in the same way as other boilers and undergoes consistent heating as it moves through the system. It’s secondary plate heat exchanger diverts hot water from the combi boiler’s primary heat exchanger to taps and other fixtures. The secondary heat exchanger is itself heated by its counterpart.
What Causes Heat Exchanger Faults?
Like any boiler part, heat exchangers can fail due to long-term wear and tear. However, there are two common boiler issues that, if not addressed, can result in heat exchanger failure.
Limescale
Over time limescale can build up in areas of the boiler where water is present. This takes up internal space, leading to potential overexertion. If left untreated, limescale can cause boiler inefficiency and create blockages. Limescale build-up is more common in regions with high mineral content water.
To mitigate limescale build-up, a reducer or silencer can be used. The former acts like a drain cleaner, breaking down limescale as it passes through the boiler system. A reducer will collect limescale at the filter, preventing it from getting to important parts.
Sludge build-up
Sludge can cause blockages that risk total boiler failure. It’s typically made up of rust and general debris, which is a by-product of hot water reacting with steel. Sludge often settles in radiators, becoming dislodged as water passes through plumbing and returns to the boiler.
The best way to prevent sludge build-up is with regular boiler inspections and cleaning. This will help remove sludge from the system and stop it disrupting heat exchanger functionality. You can ask an engineer to do this when your boiler is getting its annual service.
Symptoms of a Faulty Heat Exchanger
If you suspect your boiler’s heat exchanger is defective or experiencing faults, look out for the following signs:
- The boiler is making unusual noises – the type of noise will often relate to one of the above problems. With limescale build up, the temperature of water inside the boiler rises. This causes bubbles and steam, resulting in whistling sounds. In contrast, a build of sludge in a boiler system will produce a tapping or knocking.
- Boiler leakages – in older boilers, leakages will be visibly identifiable. Water dripping from the bottom of the casing most often means there has been a build-up of sludge, causing the heat exchanger to malfunction. As modern boilers are better put together, noticing a cracked or leaking heat exchanger can be more difficult.
- Presence of dirty water – this is an almost guaranteed sign of sludge in the system. An easy way to check for dirty water is to bleed the radiator, which is recommended throughout the year anyway. The presence of dark or discoloured water signifies the heat exchanger might be in peril.
Looking for Boiler Spares UK?
You can protect your boiler’s heat exchanger by conducting regular maintenance checks. The overall health of a boiler can also impact heat exchanger functionality, which can sometimes mean replacing select parts. Where a replacement heat exchanger would often cost upwards of £500, National Boiler Spares has a range of heat exchangers that are far more affordable. Whatever make or type of boiler you need help with, we’ve got you covered.