Most residential boiler heating systems are very reliable and immune to some of the mechanical problems that can plague furnace systems. Unfortunately, they can still suffer from serious problems if they are not properly maintained. One of the most common symptoms of boiler malfunctions is loud, unusual noises coming from the boiler and/or radiators.
A number of underlying problems can cause boilers to make strange noises. Sludge build-up in the boiler's heat exchange is one of the most serious potential causes and can cause catastrophic damage if the problem isn't fixed quickly.
What Is Boiler Sludge?
The water inside your boiler system comes into contact with large amounts of ferrous material, such as the steel surfaces inside the radiators. The water reacts with these ferrous components to produce a type of iron oxide, known as magnetite. Over time, magnetite created by these reactions accumulates into an unpleasant, black substance known as sludge.
Sludge is a thick, semi-liquid substance that is considerably heavier than the water inside your boiler system. Because of this, sludge deposits can settle in various locations within the boiler system, such as the bottoms of radiators and inside the system's circulator pump. If sludge starts to settle within the boiler's heat exchanger, the boiler may start making strange noises.
Why Does Heat Exchanger Sludge Make Boilers Noisy?
Your boiler's heat exchanger is made from a series of narrow pipes, which are heated by the boiler's electric, oil-fired, or gas-fired heating system. As water passes through these narrow pipes, it is heated very quickly, and subsequently pumped into your system's radiators to provide useful ambient heat. Unfortunately, sludge can also be pumped into the heat exchanger.
Because heat exchanger pipes are so narrow, they can easily become blocked by small amounts of thick, viscous sludge. This prevents water from passing through the blocked pipe(s) quickly enough, causing it to overheat and boil. This boiling water can make a tremendous amount of noise, leading to a noisy boiler.
If small amounts of sludge are passing through the exchanger and causing transient blockages, you may only hear some occasional knocking or scratching noises coming from your boiler. However, if some of the heat exchanger's pipes have been completely blocked with sludge, the water boiling within will create a constant, rumbling noise.
This noise is sometimes referred to as 'kettling', and spells serious trouble for any boiler. Boiling water can seriously damage the delicate copper pipes that make up a heat exchanger, and the longer the kettling goes on, the more damage will be done. Heat exchangers are expensive and very difficult to repair, so even short periods of kettling can cost you hundreds of dollars.
How Can You Prevent Heat Exchanger Sludge Damage?
With regular maintenance, you can prevent sludge build-up inside your boiler system before it starts.
Bleeding your radiators regularly is important because it removes excess air from the system, but it is also a useful time to check for sludge build-up. Keep an eye on the water that comes from your radiators when you bleed them — if it is noticeably discolored a black or gray color, your system contains significant amounts of sludge.
The easiest way to remove sludge in radiators is to flush them. You can do this yourself by opening the thermostatic valves attached to your radiators, which will allow the sludge to drain away (make sure to have a bucket or some towels ready!). If you are unsure or uncomfortable with doing this yourself, call in a residential boiler repair service to do the job for you.
However, if your boiler is already making kettling noises, it's probably too late for preventative maintenance. Switch the boiler system off as quickly as possible, and call in a professional residential boiler repair service to inspect your boiler and determine the source of the noise. These services can also replace damaged heat exchangers, and give you advice on how to prevent future sludge problems.