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How Long Does Radiator Inhibitor Last?


It depends on your system. Generally, you should expect your radiator inhibitor to last about a year. We always advise our clients to top their radiator inhibitors at least once every twelve months.

Despite being a wonder chemical, radiator inhibitor doesn’t last forever. With time, it will dilute until it’s no longer effective. How fast it disintegrates is determined by several factors, like your system’s size.

There are plenty of radiator inhibitor kits available in the market that can help test its activity levels. If the inhibitor level is too low, you’ll have to top it up.

When topping up, we advise you to regularly use the same brand of radiator inhibitor to avoid mixing different chemicals. Different manufacturers use different additives. If you mix them, they will negatively affect your system.

What is a radiator inhibitor?

First and foremost, radiator inhibitor is also known as Central Heating Inhibitor. We understand the confusion. The term “inhibitor” sounds controversial. It sounds like something that would hinder your heating system from functioning well.

The Central Heating Inhibitor is actually a “special” chemical solution that boosts radiators’ efficiency and prolongs their lifespan. Although it’s less talked about, believe it or not, it’s a component that’s just as crucial as your boiler. It keeps the entire system going.

Don’t believe us? Did you know that you can void your system’s warranty if you don’t maintain the recommended inhibitor levels? Go ahead and read your user’s manual. There’s a section on it.

Unfortunately, it’s not the most physically appealing solution. Depending on the manufacturer, it might be pale yellow or clear.

We know it might not concern you, but we’re pleased to announce that the solution contains Potassium Tetraborate Tetra-hydrate, Di-sodium Molybdate, Sodium Nitrate, and 2 2′ 2” Nitrilotriethanol.

What does the radiator inhibitor do?

As hinted earlier, the radiator inhibitor keeps the entire system going.

Sure, your central heating system might be highly efficient and hardworking. However, as the years go by, it will still fall prey to evils like limescale, rust, and erosion. It’s even worse when they join forces to form “sludge.” It’s a thick, gooey, and stubborn substance that accumulates in central heating pipes and radiator floors. It’s not good.

Not only will sludge accelerate corrosion, but it will also disrupt water flow and lower the entire system’s efficiency. In the end, you’ll not get the amount of heat you prefer and expect from your central heater.

In retaliation, some people tune to higher settings. It might work. However, you’ll end up spending more on electricity bills than is necessary.

That’s not all. Sludge might trigger pipe blockages, bursts, high boiler pressure, and all other boiler-related nightmares.

Don’t be afraid. Not all is lost.

The radiator inhibitor is the agent responsible for fighting these evils and keeping the entire system in good condition. The mix of chemicals in the solution will break down ” the sludge” before it has any chance of accumulating. Afterwards, you can power flush your system to remove the remains.

Misconception: Radiator Inhibitor removes sludge

Please bear in mind. We said it “breaks down” sludge, making it easier to remove. There are several other ways to remove those pesky remains and leave the inside of your system sparkling cleaning.

You can install a filter. Preferably, you’ll want a magnetic filter. Not only will it trap dirt, but it will also attract and trap rusting metallic pieces. The filter will then hold onto the unwanted materials until they are removed in your next boiler service. The engineer will simply remove the filter and dispose of its contents.

“Poweflushing” is the other way to remove sludge remains. It’s a crucial procedure that involves forcing a chemically infused solution through your system at high pressure. It will then wash away all dirt and rust particles.

Benefits of radiator inhibitors

So far, we’ve only mentioned the importance of the chemical solution. Besides general smoothness, below are some benefits of using radiator inhibitors and maintaining their levels.

  • Of course, its main purpose is to break down sludge and other internal radiator dirt significantly boosting the radiators’, pipes’ and boiler’s life expectancy.
  • It boosts efficiency. You’ll never have to face the cold winters in your house. The radiator inhibitor will enable your system to heat up faster.
  • You’ll save money. First, you’ll rarely have to replace your radiators or pipes because of rust infections. Additionally, you’ll save the cash you’d have otherwise spent hiring heating engineers. Finally, because of the boost in efficiency, you’ll end up spending less on fuel heating expenses.

When to start using radiator inhibitor

Start immediately. However, don’t rely on it to fix all your problems. If you’ve only recently bought the house and have no idea how old the system is, you are better off with Power-flushing.

Radiator inhibitors will not magically wash away years of sludge accumulation. If it’s the first time, we advise you to use it as a secondary cleaner followed by a power flush.

Again, after the power flush, you should add the inhibitor to prevent sludge buildup.

How to add central heating inhibitor to your combi boilers

We acknowledge the fact that Combi boilers are the most popular boilers in the UK. Below is a step-by-step breakdown of how to add it to your system.

Warning: It’s easy. There’s no need to call the professionals. You only need this guide, your preferred inhibitor, and a set of tools.

What you’ll need for this procedure

  • A can of radiator inhibitor.
  • An adjustable spanner.
  • A hosepipe connecting to a drain.
  • Your radiator key.
  • A Jubilee clip.
  • Flat-headed screwdriver.
  • Towels (To soak any leaks).
  • A funnel (It’s not necessary if the inhibitor bottle comes with a dosing adapter).

Step 1: First, make sure your central heating system and radiators are turned off completely and allow them to cool. As you wait, you can go ahead and bring your drain-able hosepipe. Tighten the pipe with the Jubilee clip.

Step 2: Select one of your radiators. The procedure will only take place on one unit. Ideally, it should be closest to the hosepipe.

Step 3: Using your radiator bleed key, open the drain valve and allow water to flow out. The amount should be equivalent to the amount of radiator inhibitor you want to add to the system. Once you’re done, turn off the drain valve.

Step 4: Using your adjustable spanner, open the radiator bleed plug and attach your funnel (or dosing adopter).

Step 5: Pour in the radiator inhibitor.

Step 6: Once you’re done adding the inhibitor, remove the funnel (or dosing adopter), and re-tighten the radiator’s bleed plug.

Step 7: Check your boiler’s pressure gauge. The ideal pressure should be around 1 to 1.5 bar. If the pressure has dropped, you can top it up by repressurizing.

When repressurizing, we advise you to allow the pressure to pass the 1.5-mark slightly.

Now, go ahead and bleed your radiator so the pressure falls somewhere between 1 and 1.5 bar. The act of bleeding will help boost the inhibitor’s circulation.


Generally, your radiator inhibitor will last for one year from the time it was introduced to your system. To be sure, you can always use an inhibitor test kit to confirm the levels.

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