Your boiler is full of individual parts that work together to allow the unit to heat your home and provide hot water for your taps. The component that is responsible for passing heat from the burner to the water is the heat exchanger.

Within this apparatus, hot gas flows over a series of pipes. Cold water runs through these pipes and, as the hot gas moves around the pipes, it heats the water to a set temperature. Without the heat exchanger, the water for your radiators couldn’t be warmed up, making your boiler redundant.

The heat exchanger is subject to constant temperature increases and decreases. When the hot gas is flowing through it, the metal will expand and when the water begins to cool down again, the metal will contract. The frequent temperature differences can cause the metal to become weakened over time and it could eventually crack.

It can be difficult to determine whether your boiler’s heat exchanger is damaged when you can’t see it. You should never try to remove the boiler casing, as this should only be done by a Gas Safe-registered engineer and you could void any warranties if you attempt it yourself. However, there are some signs and symptoms that you can look out for before calling a professional.

What are the symptoms of a damaged heat exchanger?

Below, we’ve listed some symptoms that you can look out for to determine whether your boiler’s heat exchanger is damaged. It’s worth noting that some of these could also be a sign of other underlying problems. If you’re worried about the safety of your gas boiler, it’s best to call a suitably qualified heating engineer to take a look.

Yellow or distorted flames

When the boiler is on, the burner flame should be steady and blue in colour. If the flame is yellow and is moving around a lot, then this could either be a sign that the burner is dirty or that the heat exchanger has a crack.

Leaking water

A crack can cause the heat exchanger to leak water. This water will likely drip out from the bottom of the casing. If you’ve noticed a leak and can’t seem to find where it’s coming from, call a heating engineer to take a look in more depth for you. 

Carbon monoxide alarm is sounding

You should have a carbon monoxide alarm located near your boiler. This will alert you to any potential leaks that could lead to carbon monoxide poisoning. If your alarm is sounding, you should turn your boiler off and don’t turn it back on until the appliance has been fully checked over by a heating engineer. The carbon monoxide could be coming from a crack in the heat exchanger or you may have a blocked flue. Either way, the problem needs to be resolved as soon as possible. 

Odd smells

A cracked or damaged heat exchanger could release an unusual smell similar to that of formaldehyde. This chemical smell can cause headaches and other symptoms, such as watery eyes. 

Banging or whistling noises

If you live in a hard-water area, you may have noticed limescale in your washing machine, on the end of your taps or even in your kettle. It can be a nuisance. This chalky substance can form on any appliances that use water, including your boiler. Over time, the water in the heat exchanger can cause limescale to build up.

This limescale can cause blockage and inefficiency. When it does, it causes the water to get hotter too. As the water comes to a boil, the build up of bubbles and steam will cause a whistling noise. This is also known as kettling. Limescale can eventually lead to a cracked heat exchanger, so it’s important to have the appliance cleaned annually.

How to remove a heat exchanger

Remember, never attempt to remove a heat exchanger yourself.  When the suitably qualified heating engineer comes to remove or check the unit, it’s likely that the boiler will need to be off and completely cool. Do this in advance of their arrival. They will need full access to the boiler, so ensure that there’s sufficient space for them to work easily and quickly. 

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