Water Heater Flushing: Hose, Sediment and Clogged Drain Valves

Plumbers typically charge $250 to $500 to flush a water heater, according to plumber Roger Wakefield, yet he says a homeowner can do it, and he shows the method on a cutaway Bradford White trainer.

Why sediment matters

Sediment builds up in the bottom of a gas water heater tank, and in an electric one it also collects on the elements. Wakefield says this lowers the efficiency rating, so it costs more and gives less hot water.

When not to start

He advises against beginning to flush an older tank. If it is over 3 or 4 years old, he would probably not flush it, because sediment may be what is keeping it from leaking. He says that if flushing was not started at the beginning, microscopic cracks plugged with sediment could reopen. The label's serial and model numbers can help work out the age.

The flushing steps

• Shut off the cold water valve, ideally a full port ball valve that turns 90 degrees.
• On a gas heater, turn off the gas at the control valve or turn it down to vacation so it does not fire while flushing.
• Make sure hot water faucets in the house are closed, then crack the drain valve over a towel to see whether it drains. With the vapor lock, water should not pour out.
• Connect a garden hose, which uses a hose thread, and run it to a safe area or a bucket. He sometimes covers a bucket with a white t-shirt to see calcium and magnesium.
• Open the drain valve, then open the cold water valve. The heater should sound like water is flowing.

He says it should take five or 10 minutes to get most sediment out, and it can run longer while sediment still comes out. Then close the drain valve and disconnect the hose. He leaves city water pressure on rather than draining the tank completely.

If it will not drain

Close the valve, remove the hose, keep the towel under it and poke silver solder or a wire into the open valve to break up sediment at the lowest point in the tank. If that fails, replace the drain valve with a 3/4 in. brass nipple, 3 or 4 in. long, and a 3/4 in. full port ball valve with female threads on one end and male hose threads on the other. He notes most drain valve openings are about 3/8 in. and slow the flow. Use Teflon tape and pipe dope, expect some water, and since it is hot, run hot water first to cool things down. Check for leaks afterward.

Why not drain fully

He dislikes disconnecting and draining the whole tank because of thermal expansion. He thinks the tank shrinks and grows as it cools and heats, which could cause cracks that leak later.

Results

He says flushing makes the heater more efficient, helps it last longer and gives more hot water for longer periods.