Faulty heat exchanger

faulty heat exchanger

Faulty heat exchanger – how to tell & how to fix

Boilers are incomplete without the heat exchanger. It is responsible for efficiently transferring heat from hot gas to cold water which is sent around your central heating system.

Your boiler wouldn’t heat water without it, it is like the stomach of your boiler transferring energy from food to fuel your body.

What is a boiler heat exchanger & how do they work?

Your boiler’s heat exchanger is an internal component that converts energy from gas to heat. It heats up the water you are supplying through the flow pipe.

The heat exchanger heats up as the gas burns. The coiled structure is connected to cold water. As the water circulates, the heat from the burning gas is converted to cold water. This creates hot water for heating and hot water for your taps.

inside boiler heat exchanger

After the water is heated, it circulates around your system (your radiators or heated towel rails) and then returns to the return pipe to be reheated once again. The process continues until the desired temperature is reached in your home.

Secondary Heat Exchangers

Modern condensing boilers have a secondary heat exchanging unit that captures heat from escaping gases. This improves the boiler’s efficiency.

Most heat exchangers can be made from either stainless steel or aluminum. Because stainless steel offers greater protection against corrosion and other physical damage, it is considered more reliable.

How long do heat exchangers last?

Deepening on the type of heat exchanger you have will depend on how long it will last. The two main types of heat exchangers are aluminium heat exchangers and stainless steel heat exchangers.

Aluminium heat exchanger

Aluminium heat exchangers last between 2 and 10 years depending on the quality of the boiler and this changes from manufacturer to manufacturer. 

Stainless steel heat exchanger

Stainless steel heat exchangers are far better than aluminium ones and are used in the best combi boilers. These are expected to last over 10 years, with many boiler brands offering at least a 10-year warranty on their heat exchangers, if not the whole boiler itself. 

Often, though, the cause of a faulty heat exchanger isn’t the heat exchanger itself, it is usually a bad installation, other faulty parts or blockages from limescale or sludge. If it is completely your heat exchanger, check out the latest new boiler costs online as it may be a cheaper long-term option!

Common problems of a faulty boiler heat exchanger

The heat exchanger, like any other part of a boiler or central heating system, can experience faults.

There are two main things that can often cause a faulty boiler heat exchanger or problems, apart from general wear and tear or a cheap and nasty boiler.


Limescale build-up

Limescale build-up is a lot more common in hard water areas. If you know you are in a hard water area or your kettle, iron, or rims of your taps often get this white build-up, then it is likely your boiler and heat exchanger will too.

Central heating sludge build up

This is often a more common cause of boiler heat exchanger problems. If the sludge gets into a boilers heat exchanger then it can start to clog it up and cause problems or inefficiencies. The best thing about central heating sludge buildup is that it is potentially curable.

Limescale buildup: Common symptoms

Gas boiler lockout

To protect you and your boiler, an NTC thermistor is installed in your boiler to monitor the water temperature. The boiler will be shut off if it detects excessively hot water to prevent any further damage or a boiler overheating.

Whistling and Kettling Sounds

Limescale deposits can lead to overheating in the system. This can result in steam and bubbling that can make whistling sounds called kettling.

Leaky Boiler Heat Exchanger

leaky boiler heat exchanger

Overheating can cause cracks to form and break the seal in heat exchanger components, making them leaky. These leaks are usually found at the bottom of your boiler casing, and should be removed every now and again.

Heat exchanger problems are a bad sign. It is not a good idea to spend so much money on an old boiler when heat exchanger repairs can cost upwards of £500.

You should be able to spot the problem as soon as possible. Don’t hesitate to call a Gas Safe engineer for assistance.

To prolong the life of your heat exchanger and prevent limescale accumulation, you can also do these things:

What to do to prevent a broken heat exchanger

You can seek the help of a Gas Safe Engineer if you suspect limescale buildup.

A limescale inhibitor will help to dissolve limescale and act as a cleaner.

You can also install a limescale remover. This will collect limescale as it passes through your filter.

inside boiler fixing heat exchanger

To check for any damage to your boiler, including the heat exchanger, you need to do a thorough inspection.

Even if limescale is not an issue, central heat exchanger sludge can also cause problems. This happens when water particles mixed with rust inside radiators and pipes create a gooey liquid.

Sludge can cause your heating system to slow down, which can lead to annoying radiator cold spots. Sludge can also cause corrosion and blockages over time.

Heat exchangers are particularly vulnerable because the heating water passes through them continuously, so any sludge will make contact.

There are steps you can take to remove sludge from your system and prevent it from building up again.

  • A Gas Safe engineer will inspect and clean your heat exchanger.
  • Get your system thoroughly cleaned by a power flush.
  • To prevent future sludge buildup, install a filter that collects any toxic residues.

Common Signs that a Heat Exchanger is Damaged

Leaking Water

A crack in the heat exchanger could lead to a leak where water collects in the boiler’s casing. If you are unable to locate the source of the leak, a Gas Safe engineer will be able to assist you.

Yellow or Distorted Burner Flamingo

The burner flame should remain steady when the boiler is turned on. It should also be blue in colour. If the flame flickers or moves a lot, or is yellowish in colour, it could be a cracked heat exchanger or dirty burner.

gas safe engineer

Strange Smells

Sometimes, cracks in heat exchangers can release an unusual smell similar to formaldehyde. This smell can cause headaches, as well as other symptoms like watery eyes and eye irritations. Contact a Gas Safe engineer immediately if you notice this odour.

Water that is dirty from bleeding radiations

You’ve probably ever tried to flush radiators. After the air is gone, water comes out.

If the water is turning black from the radiators, it’s likely that there is sludge.

This is because the dirty water flows through your heat exchanger and can cause a blockage.

Is it possible to repair a damaged heat exchanger?

It is not practical to fix a boiler that has a broken heat exchanger because the labour and parts costs are high. This is the truth:

Your boiler type may be relatively new and will likely be under warranty. Any repairs will be covered.

The boiler will not be covered if it is older. It is also likely to be in constant decline.

What is the difference between replacing a heat exchanger and replacing your boiler?

A new heat exchanger will typically cost between £450 and £650. This is a large bill to pay if your boiler is older than its warranty has expired.

It is usually more economical to replace the boiler than to fix other problems.

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