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Last updated: 4th April, 2024


What Is A Chemical Flush?

What Is A Chemical Flush?

Boiler maintenance can be a tricky process, and an advice guide can help a lot.

As soon as your heat cuts out, your top priority is to get it fixed, but there are dozens of things that can go wrong with your central heating system. A small amount of maintenance on your boiler can work wonders.

We've put together advice for you on chemical flushes, so you can learn exactly why they are so important. Read on below, for further information about the chemical flush and the magnetic power flush!

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What is a Chemical Flush?

A chemical system flush is a simple process designed to clear rust out of the insides of the pipes of your central heating system.

You just pump some chemicals in, and they work to clean out blockages, allowing hot water to flow more easily to ensure that things stay hot.

It usually happens when a new boiler is installed in your heating system, but if you're finding cold spots in your boiler system even without a new boiler, then it's high time to get this fixed.

Why Do I Need a Chemical Flush?

Over the years, rust can build up in the pipes of your central boiler system, preventing hot water from travelling around the system. A chemical pump cleanse is a great way to get a number of blockages flushed out, letting hot water into all the cold spots in your system.

It's important to keep your pipes clear of rust so water can flow through them cleanly and efficiently, and a chemical flushing can enable that. It's cheaper than magnetic cleansing and may not need the help of an engineer, and it doesn't take a long time.

What Are the Benefits of a Chemical Flush?

A chemical boiler cleanse will help to clear all of the inhibitor debris and sludge from the insides of your central heating system.

This will help to ensure that the hot water reaches every part of your home, as well as generally improving the energy efficiency of your heating and helping saving money and energy in the longer term. As standard, it will prevent radiator damage for a while, and it doesn't even take a long time.

How Often Should I Get a Chemical Cleanse?

A chemical flush is a major piece of standard boiler servicing, and you'll be pleased to hear that you don't need to use this type of maintenance on a regular basis. Most boilers will only need a few chemical system flush services over their entire lifespan!

The answer to when you need to perform a power flush may vary from boiler to boiler, but asa general rule, if the bottoms of your radiators are still cold even when your heating is switched on, you may want to look into a chemical flush.

Always do it when a new central heating pipe system, radiator, or inhibitor is installed, as these tend to have all sorts of loose debris from the installation process, and you will want to prevent damage.

How Much Does a Chemical Flush Cost?

There are several different variables that may affect the costs of a power flush, which could make this answer a more complex one than you might like.

These include things like the age of your central hot water system and the size of your central heating system. Usually, the cost is between £300 and £700 - the cost could be lower, but probably not much, and may well be higher for a larger flushing.

Don't let that price put you off, though, as the increased efficiency you could get will offset that soon enough, and you should try to prevent further damage.

How Long Does a Chemical Flush Take?

In most cases, a chemical clean will take a few hours to complete. This will depend on how large your central heating system is; if there are more radiators in need of flushing, it will take more time to fully flush the system out. After a few hours, though, you'll feel the benefits as your heating system starts to work properly again.

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Chemical Flush vs Power Flushing

A chemical cleanse and a power flushing are very similar things, but there are a few important differences you will need to bear in mind. A chemical flush consists of pouring a number of chemicals into your heating system and leaving them to circulate for a while.

These chemicals break down the debris and sludge in your central heating system, and then you can flush the loose remains out of the system with clean water.

A power flushing, however, is a much deeper and more thorough cleanse. In this type of servicing, chemicals are also used, but they are blasted through your pipes with a high-pressure pump in order to completely annihilate every trace of sludge. This is more effective, but it's usually more expensive, too!

Chemical Flush vs Magna Cleanse-

We've already summed up the flush options above, but what about a Magna cleanse? Well, the magnetic cleanse is probably the most advanced option for cleaning and servicing your central heating system.

This is a thorough cleaning option based around the magnetic attraction that removes even the most stubborn and difficult scaling, sludge, and magnetite’s. It's a faster and more powerful option but can be a bit more expensive.

That being said, it can be worth installing a number rated magnetic filter (safely registered in England) onto your heating systems to help filter out sludge constantly while your boiler is operational, keeping the gunk out of your radiators.

A magnetic cleanse isn't always what you need, and flushing might be enough, but it could be worth considering for stubborn sludge.

Chemical Flush Questions (FAQs)

Can You Power Flush a Combi Boiler?

Yes. A combi boiler can be easily flushed, just like any other type of boiler. If you're installing a new boiler on an old system, it's worth doing a power flush before installation, just to avoid contaminating the boiler with old debris and dirty water from inside your radiators that could damage it.

Can Power Flushing Cause Boiler Leaks?

You might have heard that a chemical boiler cleanse is a safer option than a power flush because a power flush can cause leaks in your pipes, but that is not true.

Both a chemical boiler flush and a power flush are very unlikely to produce leaks in your pipes. In fact, the only risk is that a flush washes away some debris that was blocking up a leak in your radiators that already existed.

Can You Power Flush a Microbore Boiler System?

Microbore central heating uses extremely narrow tubes, which can cause problems if you try to clean them with power flushing. In this case, it is better to use a chemical cleanse than a power flush.

Can You Perform a Chemical Flush on Your Central Heating System Yourself?

While you can perform a chemical wash at home yourself, that might not be such a great idea. If you try to service your boiler on your own and something goes wrong, that's your fault, and you won't be covered for any damage.

It's also a messy job, and you'll probably get wet and dirty in the process. Hiring a gas safe engineer (properly authorised and regulated by the financial conduct authority in England and Wales) is the best bet here, as engineers will be able to service your radiators effectively without breaking warranty.


A chemical wash is a great way to keep your central heating working properly and effectively. If you're starting to worry that your radiators are blocked up, find a gas safe engineer (authorised and regulated by the financial conduct authority) to service your central heating properly and get everything working again.

You'll find that it pays for itself soon enough in reduced bills and greater energy efficiency! Even if you're not sure, engineers are abetter bet than having to buy new boilers, dealing with a credit broker and a panel of lenders!

Looking after your radiators and heat exchanger is the best way to ensure comfort in the winter months.

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Frequently Asked Questions

How Long Does a Chemical Flush Last?

The longevity of a chemical flush's effectiveness in a heating system largely depends on the system's condition before the flush, the quality of the water in the system thereafter, and ongoing maintenance practices. While a chemical flush can provide immediate improvement, its effects are best maintained through regular system checks and by addressing any water quality or circulation issues promptly. It's not so much about how long a chemical flush lasts but how well the system is maintained to prevent sludge and debris accumulation in the future.

What is the Difference Between a Power Flush and a Chemical Flush?

Power Flush: This is a more intensive cleaning process designed to remove sludge, rust, and debris from a heating system using high-velocity, low-pressure water combined with specialized cleaning chemicals. It requires professional equipment and expertise and is suitable for systems with significant blockage and circulation issues.

Chemical Flush: A less invasive method than a power flush, a chemical flush involves adding specific chemicals to the system, which circulate to dissolve sludge and debris. The system is then drained to remove the chemicals and dislodged materials. It's often used as a preventative measure or for systems with minor issues.

How Much Does a Chemical Flush Cost?

The cost of a chemical flush can vary depending on the size of your heating system and the rates of the service provider, but it typically ranges from £100 to £300 in the UK. This cost is generally lower than that of a power flush due to the less intensive nature of the work and the lack of need for specialized equipment.

Does Chemical Flush Remove Sludge?

Yes, a chemical flush is designed to remove sludge, as well as rust and other debris from a heating system. The chemicals used in the flush are formulated to break down these materials, making it easier to flush them out of the system and improve heating efficiency and system lifespan.

How Effective is a Chemical Flush?

The effectiveness of a chemical flush can vary based on the extent of sludge and debris buildup and the condition of the system. For systems with moderate levels of buildup, a chemical flush can be quite effective in restoring efficiency and improving circulation. However, for heavily blocked systems, a power flush might be necessary for comprehensive cleaning.

How Much Does a Power Flush Cost UK?

In the UK, the cost of a power flush can range widely, typically between £300 to £600, depending on the size of the system, the extent of contamination, and the geographical location. Larger systems or those requiring significant cleaning may incur higher costs.

How Does a Plumber Do a Power Flush?

A plumber or heating engineer performs a power flush by connecting a power flushing machine to your heating system, either at the circulation pump or a radiator. The machine pumps water and specific cleaning chemicals at high velocity through the system but at low pressure to avoid damage. The flow of the water is frequently reversed to dislodge and remove all traces of sludge and debris. The process involves several stages, including pre-flush assessment, chemical treatment, targeted flushing of radiators and pipes, and finally, a post-flush system check to ensure cleanliness and proper operation.

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Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.