How often should you flush your water heater?

Why bother

Sediment shortens its life and saps efficiency. This is an essentials-tier job. Skip it and you're inviting the expensive kind of problem, or the dangerous kind.

Why it's a range

On hard water it wants doing every six months; on soft, every year or two is plenty. A year is the safe middle. The people quoting six months at everyone tend to be the ones charging to do it.

What the job involves

1. Cut the power and let it cool. Flip the breaker for an electric unit, or set a gas one to 'pilot', then shut the cold-water valve on top. Give it a couple of hours so you're draining warm water, not scalding water.
2. Hook up a hose and drain it. Screw a garden hose onto the drain valve at the bottom, run the other end to a floor drain or outside, open a hot tap somewhere in the house to break the vacuum, then open the drain valve.
3. Flush until it runs clear. Once it's empty, turn the cold supply on and off a few times to stir up the muck and rinse it out. Keep draining until the water from the hose stops coming out cloudy and rusty.
4. Refill and switch back on. Close the drain valve, take the hose off, reopen the cold supply, and wait for a steady stream at the open tap, about 15 minutes, before you turn the power or gas back on.

Do it yourself, or pay someone?

Yourself, for most homes. It's a garden hose and an afternoon, and it's the cheapest thing you'll ever do for the tank. Pay a plumber if the drain valve is seized, the water won't run clear, or you'd rather leave the gas and electric alone: a professional flush runs $110 to $200, around $160, with a plain tank model at the low end ($75 to $150).

What skipping it costs

$882 to $1,817 is what a new water heater runs, national average about $1,340, and a neglected tank brings that bill forward by years. Sediment settles into a hard crust on the floor of the tank, where it insulates the burner from the water (so the heater works harder and the energy bill creeps up) and corrodes the steel from the inside. A tank that should give you 10 to 15 years can have its life cut roughly in half. The flush that prevents all that is $75 to $150 if you pay someone, or a hose out the bottom once a year if you don't.

Signs it's overdue

• Popping, rumbling, or crackling from the tank. Sediment traps a layer of water underneath it, and that water boils and pops steam against the crust (Rheem, This Old House).
• Rusty, brown, or sandy hot water, or a whiff of rotten egg. That's sediment and corrosion stirred up inside the tank (This Old House, Energy Trust of Oregon).
• You run out of hot water sooner than you used to, or it takes an age to reheat. Sediment eats into the tank's volume and insulates the heat source, so capacity and recovery both drop.

When to start thinking about it

Give yourself about 7 days' notice. That's when Grumpty starts grumbling, so it doesn't land on you the day it's due. Mark it done and Grumpty sets the next one, every 12 months, so you can go back to forgetting it exists.

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