Water heater flushing

Why sediment builds up

Water in much of the San Gabriel Valley carries dissolved calcium and magnesium. When a tank heats that water, some of the minerals drop out and settle on the bottom as a gritty layer.

Over a few years the layer can get thick enough that the burner on a gas heater is heating rock before it heats water, and the lower element on an electric heater can get buried. Tankless heaters have the opposite problem: scale coats the inside of the narrow heat exchanger and chokes flow.

The signs are familiar. A tank heater rumbles, pops or crackles while it runs. Hot water runs out sooner than it used to, because sediment takes up space.

Water from the drain valve comes out cloudy or sandy. On tankless units, the display may show a scale or flow error code, the water temperature may swing, or hot water takes longer to arrive.

How a tank flush works

1. We turn the gas control to pilot or vacation, or switch off the breaker on an electric unit.
2. We shut the cold supply, open a hot faucet to break the vacuum, and attach a hose to the drain valve, running outside or to a drain.
3. We drain the tank, then open and close the cold supply in bursts to stir up sediment and push it out.
4. We run until the water comes out clear, then close the drain, refill the tank completely, bleed air from the faucets and relight or power the heater.
5. We check the drain valve for drips once the tank is under pressure.

Older plastic drain valves sometimes clog with sediment or will not reseal. If that happens, we replace the valve with a brass full-port valve, which drains faster and holds up better on future flushes.

Descaling a tankless heater

Most tankless units have isolation valves with service ports. We close the valves, connect a small pump and hoses to the service ports, and circulate a descaling solution recommended by the manufacturer through the heat exchanger for the time listed in the manual.

Then we flush with clean water, clean the inlet water filter screen, reopen the valves and check the unit's error history. Your manual will list how often the maker recommends descaling, which depends on water hardness.

When a flush will not help

A flush cannot fix a tank that is already leaking from the body, rust coming from a failed tank lining, or a burner problem. On very old tanks with heavy buildup, a flush can sometimes loosen debris that then clogs the drain valve or exposes a weak spot. We look at the age on the label and the condition of the tank before starting, and if a tank is near the end, we tell you so you can decide whether to put money into maintenance or into a replacement.

Pair it with a quick check-up

While we are at the heater, we look at the seismic straps, the vent connection, the relief valve discharge pipe and the flexible connectors. California Health and Safety Code section 19211 requires residential water heaters to be "braced, anchored, or strapped," and a flush visit is a good time to confirm yours is. If the relief valve has been dripping, we check house water pressure, since high pressure or a missing expansion tank is a common cause.

What to send

Text a photo of the full heater, the label with the model and date, and the drain valve area to (310) 628-9399. Tell us where the hose can drain. We reply with questions or a quote.

If the drain valve drips afterward

Many tanks ship with a plastic drain valve, and it can drip after being opened, especially when a grain of sediment settles in the seat. Opening and closing it fully a couple of times with the water on often clears the grit.

If it keeps dripping, the valve needs replacing; a garden hose cap threaded onto the outlet stops the drip until then. A brass replacement valve is sturdier and easier to open for the next flush.

Signs your tank is overdue

Popping during heating, a drain that runs cloudy for a long time, hot water that turns lukewarm sooner, and higher gas use for the same hot water. A flush may help on a younger tank. On a tank near the end of its life, it can be a sign that replacement is coming.

Anode rods

The anode rod is a sacrificial metal rod that protects the tank. When it is used up, the tank corrodes. Many anode rods can be reached from the top of the tank.

If yours can be removed, a flush visit is a good time to check it. A rotten-egg smell from hot water sometimes comes from a reaction between the anode and water; a different anode type can help.

More questions

Will flushing void my water heater coverage? Most makers recommend periodic flushing in their manuals. Check your manual.

Can sediment clog my faucets? Yes; loosened sediment can reach aerators. Clean them after a flush.

Electric tank notes

Electric heaters have elements that scale up in hard water. A flush helps, and a burned-out element can be replaced on the same visit if it tests open.