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How can rust affect my boiler?


How can rust affect my boiler?

Rust happens when the metal of your boiler corrodes – it’s the basic reaction that happens with metal and water in the presence of oxygen. Since your boiler is basically a big metal thing that circulates water and you’d expect it to last for 15 years or more, you’d expect rust to be a constant and endemic problem. Thankfully, it generally isn’t. 

Mostly because the boiler manufacturers go to some lengths to make them resistant to corrosion. And that’s one of the reasons why it’s worth making sure you get a reliable make of boiler when it is time to invest in a new one.

Nevertheless, there are ways that corrosion can affect your boiler, and when it does you may need to get professional assistance to sort it out.

  1. Stress cracking. The metal of boilers is always expanding or contracting with the heat, and this can lead to the formation of cracks. With cracks may come the presence of oxygen, and once that oxygen is dissolved into the water, then you have the situation that will promote rust.
  2. Sediment. There may be a build-up of sediment in the bottom of your tank during heating. That can be a route in for chemicals that lead to corrosion. In that situation, you may need the tank to be flushed to remove the build-up.
  3. Low pH level in the water. A surplus of acid because of water contaminants can also promote rust.

If you start to get rust on the boiler surface (generally on the inside, of course) the patches will grow, thinning the metal until holes start to form along the boiler tank. Also you may get pitted corrosion, where small holes form – often along the pipes that come out of the boiler. Either of these could end up resulting in leaks and a costly repair bill. Even if corrosion doesn’t result in a leak, it may well impact your boiler’s efficiency and overall performance. It will have to work harder and for longer in order to reach the temperature you need – and that means higher fuel bills. 

And once corrosion gets firmly established, it will probably shorten the lifespan of the system overall. So you’ll get less return for your significant investment.

The best ways to keep the rust away are:

  • Get a good quality system in the first place, properly installed by a professional
  • Ensure the boiler feedwater is properly treated
  • As always – make sure you get your boiler serviced regularly. Once a year.


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