How to Protect a Water Heater from Corrosion and Rust
(updated 2020)

Flooded water heaterImage by analogicus from Pixabay

For most of us with a hot water tank heater in our home, whether gas, oil, or electric, the most significant variable we face is the quality of the water supply. Of course, if it's a municipal water system, it is guaranteed to be safe to consume, but it does contain elements that should do us no harm; however, those same minerals may wrecking our boilers from the inside out. How do I protect my water heater from corrosion and rust?

It's a fact that many of us don't give our work-horse water heaters enough loving care. They are a set-and-forget item, and as long as you have hot water, you don't care.

But you should.

Your water heater needs regular checking and maintenance that most DIYers can do in the blink of an eye.

The water issue is potentially worse where well-water is the source of your freshwater. It contains more solids, which can mean trouble if they get inside our boiler.

According to the EPA, there are over 13 million households in the US who depend on private wells for their water supply, and there is no oversight. Private well owners are responsible for the safety of their water supply.

What does this mean for my water heater?

Without an inline filter on your water supply, there will be a steady buildup of sediment in your water heater over time, which can wreck it.

Many contaminants are heavy, so gravity takes them to the bottom of your water tank, where they build up into a thick layer. In a gas or oil-fired water heater, the burner sits directly under the base.

When it's called to heat your water, it has to fight through the layer of sludge. It uses more energy and runs flat out as it tries to bring your water up to temperature. Because of this, it may overheat your water and cause your pressure relief valve to open up and leak.

Heating elements are at risk too

Electrical water heaters typically have two heating elements, one at the bottom of the tank and the other closer to the top. These also become coated with limescale, which affects the efficiency of the element. It has to work harder to function, thus shortening its life.

This buildup of sludge on the base of the heater creates the perfect environment for corrosion and rust to form and start destroying your tank.

Carbon steel, which is a combination of iron and steel, rusts easily and is the most common material used in water heater tanks. Chlorinated water, which is very common, is also very corrosive to carbon steel. While your water tank may have a protective coating, it is almost impossible to apply a perfectly even layer without tiny cracks or microscopic pinholes. Water will inevitably work its way through, reaching the steel where corrosion will start.

A sacrificial anode is essential in any steel boiler, even with a glass protection layer, and these need checked every couple of years and replaced as they wear out.

Stainless steel is being increasingly used for water heater tanks, but they can also corrode, especially with chlorinated water. Glass protective coatings are frequently used inside these tanks too. Higher grades of stainless steel are less susceptible to rust but are much more expensive.

Troubleshooting

You may find your water heater is running hotter than usual, and there may even be some leakage from your pressure relief valve, which is a sign of a possible issue that needs your attention. Listen to your tank. If you hear rumbling or bubbling sound, it's time to run some checks and see what's going on.

This happens especially in gas or oil-fired heaters where the burner sits under the base of the tank. It heats the water through the sludge, which causes bubbles. When they burst through, bubbling up inside the tank, you will hear them, and it's an indication your tank probably needs to be flushed.

You may also experience rusty water at your faucet, which could be because of a dirty tank that needs flushing. A good tip is to have a look inside one of your toilet cisterns. If the water tank is dirty and full of sediment, crystals, and sand, it's a sign of the likely state of your hot water tank.

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How to drain and flush your water heater tank in 14 easy steps

  1. Shut off the cold water supply to the boiler. 
  2. Switch off the power and unplug from the mains. (turn off the gas supply).
  3. Or, set your thermostat to a low setting or vacation mode. 
  4. Allow some time to let the water cool; you don't want to be working with scalding water and wear heavy-duty gloves for protection.
  5. Open a nearby hot water faucet to avoid airlocks.
  6. Connect a length of standard garden hose to the drain valve and direct it to a nearby wastewater drain or collection bucket.
  7. Open the drain valve slowly (these usually need a screwdriver to open and close. Let the water run until it's clear.
  8. If it's not clear, open the cold water valve to the heater and allow fresh water inside and then drain again until it runs and remains clear.
  9. Close the valve and remove the hose.
  10. Open the water supply to the boiler and let it refill before you power it up as you can cause damage if it's not full.
  11. Re-power/gas your heater and turn the thermostat up to a normal setting.
  12. The tank will have some air inside, which will bubble until it clears. Run a nearby faucet to help clear it.
  13. Check the drain valve isn't leaking.
  14. Run your hot water at your faucet, and it should now be crystal clear.

Check out this video, which shows you what to do, step by step.

While water heater tanks have internal protection to prevent corrosion and rusting if there is a continuous buildup of sediment, it will only add to the problem. It only takes a tiny point of access for an attack on the tank.

The first thing you may notice is a leak on the floor, by which time it could be too late to repair the tank.

Conclusion

Benjamin Franklin famously said, "an ounce of prevention is worth a pound of cure." It's still solid advice today, especially when it comes to protecting your water heater.

Make sure it's looked after and do the following few easy things:

Install an inline water filter on your water supply – check and replace the cartridges regularly, more so if your water comes from a private well.

Check and flush your water heater tank at least once a year or oftener if you use well water, live in a hard water area, and don't have a filter or water softening system installed.

Check your pressure relief valve for leakages and make sure it's operating correctly every couple of months; it could save your life.

Check your sacrificial anode every two years and replace it if necessary, they are a great deal cheaper than a new heater.

All done? You're a star! Now you can relax, and your water heater will last longer and cost you less to run.

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