Maintain it · practical guide
How to flush a water heater (and why the rumbling matters)
In one line: Sediment is the crackle and pop in the tank. The once-a-year drain that quiets it, the safety steps that come first, and the line where a pro takes over.
A water heater that crackles or rumbles while heating is telling you about sediment: minerals settled on the tank floor, trapping water that pops and steams as it tries to escape. Left alone for years, the layer insulates the burner from the water - longer heating, higher bills, and a shorter tank life. An annual flush is the standard, boring fix.
Before anything: the two shut-offs
Electric heater: switch it off at the breaker first - heating elements running dry burn out in minutes, and live elements plus draining water is a combination you never want. Gas heater: set the gas control to PILOT (or off per the manual) so the burner cannot fire while the tank drains. Cold-water inlet: closed. Then give hot water a head start by running hot at any tap until it runs warm - you will be gentler on your arms later.
The flush, in five honest steps
1. Connect a garden hose to the drain valve at the tank's base and run it outside or to a utility sink - the water will be hot, so the hose end needs securing.
2. Open the drain valve, then open a hot tap somewhere in the house (or the pressure-relief lever per the manual) so air can replace the leaving water.
3. Let it run until the water flows clear and cool-ish - minutes if flushed yearly, longer and grittier if this is its first ever flush.
4. For a deeper clean, briefly reopen the cold inlet a couple of times while draining to stir the settled layer.
5. Close the drain, close the hot tap you opened, reopen the cold inlet and let the tank fill completely - confirm hot runs full and steady at that tap again - then restore power or gas. Heating an empty tank is the classic self-inflicted kill.
When to call a professional instead
If the drain valve is fused solid or drips after closing, if the tank is more than a decade old and has never been flushed (old tanks occasionally leak once disturbed - better discovered by a pro), or if the pressure-relief valve weeps afterwards. A pro visit every few years should also include the sacrificial anode rod check - the part that dissolves so the tank does not.
Flushed yearly, a tank routinely outlives its warranty by years; neglected, it rusts quietly toward the day it fails on a weekend. Pair the habit with knowing how your heater works, finding your water main shutoff before an emergency, and the small toolkit this job needs.
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General information, not professional advice. Homes differ — if a job is beyond your confidence or the guide’s boundary, that is what tradespeople are for.