How to Drain a Hot Water Tank: Steps, Tools and Precautions

A hot water tank (water heater) is drained to descale the heating element, replace a part or shut up a house in winter. Skipping this operation causes an accumulation of limescale that overheats the element and makes it burn out prematurely. Draining a hot water tank takes between one and two hours, requires strict electrical precautions, but presents no major difficulty if you respect the order of the steps.

When and why to drain your tank

• Every one to two years, depending on the hardness of the water in your region
• The water coming out of the tap is cloudy or milky, a sign of limescale in suspension
• A drop in volume or hissing noises coming from the tank
• Before leaving in winter for an unheated house, to avoid freezing

The frequency depends directly on the hardness of your water, measured in French degrees. Above 20 French degrees, limescale settles quickly on the element: an annual drain is then recommended. Between 10 and 20 degrees, a rhythm of eighteen months to two years is enough. You can find out the hardness of the water in your area by consulting the water agency's data sheet or asking your supplier for a simple sample test. Whatever the rhythm, note the date of the last drain on the tank itself so you do not forget it.

The tools and materials you need

• A garden hose or a drain hose of 15 to 20 mm
• A bucket and cloths to catch the run-off
• An open-end wrench or an adjustable wrench for the nuts
• A screwdriver to open the cover of the heating element
• White vinegar or a descaling product to clean the element

The safety precautions before starting

The golden rule: cut the electrical supply of the tank at the circuit breaker, never settling for the wall switch. Then wait for the water to cool down, ideally several hours or overnight, because draining water at 60 degrees presents a risk of burns. Finally, close the cold water inlet of the tank, usually fitted with a tap or a valve on the safety group.

Draining the tank step by step

1. Switch off the circuit breaker of the tank and check that no indicator light stays on.
2. Close the cold water inlet valve.
3. Connect the hose to the drain on the safety group and run it towards a drain.
4. Open a hot water tap in the house to let air into the tank.
5. Open the drain and let the water run until the flow becomes steady.
6. Finish by draining the bottom of the tank: the water then comes out laden with limescale.

Cleaning and descaling the heating element

Once the tank is empty, remove the lower cover and take out the heating element (or the heating ring) with an open-end wrench. Clean it with white vinegar or a soft wire brush, then vacuum up the deposits left at the bottom of the tank. Take the opportunity to inspect the condition of the anode: a worn anode signals corrosion to come and deserves to be replaced if it is reduced to less than a third of its original size.

Restarting the tank safely

1. Replace the heating element and its new gasket, without forgetting the sealing ring.
2. Close the lower cover and reopen the cold water inlet valve.
3. Open a hot water tap until the water runs without air bubbles.
4. Check that no leak forms at the fittings.
5. Switch the circuit breaker back on only when the tank is full.

Draining before a winter absence

If you are leaving a second home for several months in winter, a complete drain protects the tank from freezing. Proceed as for a classic drain, but leave the hot water tap open and the safety group in the open position once the tank is empty, so that the smallest residual drop can drain away without freezing in the tank. Also cut the electrical supply of the home at the main circuit breaker if the house stays unoccupied, and do the same for all the other appliances containing water (boiler, washing machine). On your return, close the drain, fill the tank and check the sealing before switching the circuit breaker back on.

The mistakes to avoid

• Switching the tank back on when empty: the element heats white-hot and burns out within minutes
• Forgetting to close the cold water inlet, which prevents the drain
• Draining without opening a hot water tap: the suction blocks the flow
• Neglecting the safety group, an essential safety part of the installation

Draining a hot water tank once a year noticeably extends its lifespan and avoids element breakdowns, the number one cause of premature replacement. The key to success lies in three moves: cut the electricity before anything, wait for it to cool, and only switch back on once the tank is full. If in doubt about the anode or the safety group, a professional will carry out the drain in under an hour.