Hot tips for cleaning & flushing hot water tanks

July 28, 2015

Unless you live in a hard-water area, the cleaning and maintenance of your hot-water system is straightforward. Most hot-water tanks are powder-coated steel and the exterior models are built to withstand harsh conditions.

Hot tips for cleaning & flushing hot water tanks

1. In general

  • The outside casing of the tank should not need more than a wipe down to remove dirt and grime, and the occasional vacuum if cobwebs are a problem.
  • Check that spiders, leaves or dirt have not blocked the drainpipe.
  • Apart from that, all you need to do is remember to ease the pressure relief valve (located near the top of the heater) for around 10 seconds every six months, to ensure the correct and safe operation of your heater.

2. Counteract mineral build-up

All water contains some sediment and it can create problems for water heaters if you live in a hard-water area. You're probably already familiar with the floating stuff you see in the bottom of a glass in which ice has melted, or with minerals in the kettle. The cause, in both cases, is calcium and magnesium salts, which precipitate out of water when it is frozen or heated. To counteract this you have several choices:

  • Make sure that you install a hot-water system that is appropriate to your area. In hard-water areas, manufacturers make modifications to standard systems to allow for the higher saturation index of the water. If you are unsure of the quality of your water, seek advice from your local water supply authority.
  • Have a plumber flush the heater or install a water softener.
  • Buy a 'self-cleaning' water heater.
  • Buy a 'tankless' water heater. It's more expensive, but it's also more energy efficient.
  • Flush the heater yourself.

3. If you decide to do the flushing job

  • Turn off the heater and the cold water that runs into it.
  • Hook a garden hose to the drain valve (the one near the bottom of the tank). Make sure there are no kinks in the hose. Put the other end of it where you want the hot water from the tank to go.
  • Open the drain valve.
  • Disconnect the cold water inlet pipe on the top of the water heater to let air into the water heater so it will drain. After all the water has drained, close the drain valve.
  • Pour 4 litres (4 quarts) of a food-grade de-limer (available from plumbing supply stores and some hardware stores) into the cold water inlet pipe. Pour only 250 ml (1 cup) at a time and pause between cups. Leave the de-limer for several hours to let it do its work.
  • Drain the cleaner.
  • Reconnect the cold water inlet pipe, open the valve and let water run through the heater for several minutes, flushing out the cleaner and dissolved sediment.
  • Close the drain valve and open the hot water tap nearest to the water heater. Let the water heater fill up.
  • When water comes out of the open tap, reopen the drain valve and let the water heater rinse until the water running out appears clear.
  • Close the drain valve and open all the hot-water taps to remove the air from the heater and pipes.
  • Turn the water heater back on and remove the garden hose from the drain valve.
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