Does your water heater need to be flushed on a regular basis?

It’s a question that eventually crosses the mind of any homeowner who cares about preventive maintenance. If you’re having trouble finding a clear answer, it’s probably because it all depends on what kind of water heater you have.

Electric water heater
If you have an electric water heater and it is fed by the municipal water system, the answer is simple: there is no need for regular flushing. The consensus is that generally speaking, this operation will not have a significant impact on the heater’s useful life.

If, however, your home is connected to an on-site system (a well) that supplies poor-quality water (i.e., hard water or water with iron content), you should perform regular flushing of your electric water heater. Read the following instructions closely.

First off, it’s very important to start this maintenance routine immediately after the installation of your new heater. If you decide to drain a heater after it has been in use for several years, you may do it more harm than good. Knocking loose calcium deposits that have formed on the inside walls of the tank can cause premature corrosion.

As specified in the step-by-step procedure below, the key to an effective cleaning operation is to ensure the tank is thoroughly rinsed out before refilling.

Flushing procedure

1.   Turn off the electric power to the water heater (circuit breaker or switch to “Off” position).
2.   Shut off the cold-water inlet valve.
3.   Open a hot-water tap to let air into the tank.
4.   If necessary, connect a garden hose to the drain valve at the bottom of the tank and put the
      other end in the floor drain, in a bathtub or outside.
5.   To avoid the risk of scalding, gradually open the drain valve (or let the water cool before
      draining). Let the tank empty itself completely.
6.   Re-open the cold-water inlet valve and let water run at full pressure for several minutes to
      completely flush out any deposits from the bottom of the tank.
7.   When the water running out is completely clear, close the drain valve.
8.   Let the tank fill up. Filling is complete when water runs normally out of the hot-water tap that you
      opened earlier; i.e., once all the air has been evacuated from the tank.
9.   Close the hot-water tap.
10. Turn the power to the water heater back on.

Along with routine flushing, you must perform another maintenance task: inspect the anti-corrosion rod, or sacrificial anode, at least once every three years. This is a steel rod, typically coated with magnesium, suspended vertically inside the tank. The rod “sacrifices itself” for the good of the tank: the principle of electrolysis causes the rod, instead of the steel of the tank, to corrode. When necessary, the rod releases particles of magnesium that adhere to failing areas of the vitrified interior coating.

These “patches” can come loose during a cleaning operation, resulting in premature wear on the anode, which must start its job over again. It is therefore very important to replace the anode before its coating dissolves completely; otherwise tank will start to rust. A new sacrificial anode has a diameter of about 1.9 cm (3/4 in.). If inspection shows that it has dissolved to half that diameter or less, or if any part of its steel core is exposed, the rod must be replaced.

Gas- or oil-fired water heater
Unlike an electric model, which heats water by means of submerged elements, a water heater fired by natural gas or home heating oil has a burner under the tank. This results in a much higher heating temperature, and causes sediment to precipitate to the bottom of the tank.

Manufacturers of these types of heaters recommend regular flushing to clear built-up sediment, which hinders proper heat transfer and in turn reduces energy efficiency. These models also have a sacrificial anode, which must be inspected.

Because they contain combustion mechanisms, it is strongly recommended that you entrust draining and indeed all maintenance of these types of heaters to a qualified technician.

Leaving on vacation?
If you are planning to be away from home for several weeks, it is always wise to shut off the cold-water inlet valve and the power supply (electricity in the case of electric water heaters; electricity if applicable and gas valve for natural-gas-fired models; electricity if applicable and oil intake for oil-fired heaters).
Note, however, that you must not drain the water from the tank before leaving – a water heater must never be left empty!

When you return:

1. Re-open the cold-water inlet valve.
2. Open all the hot-water taps in the house and let the water run until the heater tank is completely
    drained – bacteria may have had time to develop in the unheated water during your absence.
3. Shut off the hot-water taps once the water runs cold, and then turn the electric power to the water
    heater back on.

Moreover, all the cold water lines in your home should be flushed out after your return. Let water run from every tap until it is cold. So that you don’t waste any of the flushed water, you can recover it and use it for cleaning, or to water your house and garden plants.