Water heater maintenance for hard-water country

What a flush is, and how often

A flush means taking the heater off gas or power, letting it cool, and draining it through a hose to carry the loose sediment out. Done properly it also means opening the cold supply while it drains, so incoming water stirs the sediment bed instead of leaving it packed, then refilling and purging the air before anything is relit. Once a year on our water; twice for a big household or a rental.

One caveat. A ten-year-old tank that has never been flushed is a judgement call, not a routine job — sediment that has sat that long can be the only thing holding a corroded drain valve together, and disturbing it can start a leak. We would rather plan a replacement with you than take your money for a flush that finishes the tank off.

Anode rods — the part that decides how long the tank lives

Every tank heater has a sacrificial anode rod threaded into the top: magnesium or aluminum hung down the middle, whose whole job is to corrode instead of the steel. While the rod has material left, it is the thing being eaten. When it is gone, the tank is next — and a corroding tank cannot be repaired, only replaced.

Mineral-heavy water consumes an anode faster, which is the mechanism sitting under the shortened lifespans here. Replacing one is a small part and an hour of labor set against the price of a whole new heater — the highest-return work anyone can do to a water heater. Two notes: some heaters use a combination anode built into the hot outlet rather than a separate port, and every rod needs clear headroom above the tank to come out.

Testing the T&P valve

The temperature and pressure relief valve exists to stop the heater rupturing: past roughly 150 psi or 210°F it is meant to open and dump. It is tested by lifting the lever, letting it discharge, and letting it snap shut.

Two things first. A valve untouched for years may not reseal after testing and will drip until replaced — a reason to have the part on hand, not a reason to skip the test. And the discharge pipe must run full size, downward, and end where a discharge would be seen and would not scald anyone. One piped into a closed drain or capped off — and we do find them capped — removes the only safety device on the appliance.

Expansion tanks, and the relief valve that "keeps failing"

If the house has a pressure reducing valve or a check valve at the meter, the plumbing is a closed system: water can come in, but it cannot push back toward the street. Heated water expands with nowhere to go, so pressure climbs every time the burner runs. The usual symptom is a relief valve that weeps every few months and gets replaced over and over, when the valve was never the problem.

The fix is a correctly sized thermal expansion tank, and the detail most often skipped is the pre-charge: the air charge has to match the measured static pressure of the house, set before the tank sees water. The bladder fails eventually too, and a waterlogged expansion tank looks perfectly fine while protecting nothing.

Where to set the thermostat

120°F is the setting worth defaulting to. It is hot enough for a household, below the point where a slip of the tap scalds in seconds, and — the part that matters here — scale forms faster the hotter the water runs, so a lower setting is slower to destroy the tank. 140°F costs more every month and buys back less capacity than people expect, because a hotter tank simply gets mixed back down at the tap. If there are specific health considerations in the house, that is a conversation for your doctor rather than a rule of thumb from a plumber — tell us where you want it and that is where we set it.