‘Spring’ into Maintenance Part 2B’


There’s only one way to do electric hot water heater maintenance, or write about it. The correct way. In order to cover all the information sufficiently, we’ve needed a few extra posts. This month we’ll finish our discussion and I’ll tell you how to flush your hot water heater and check your expansion tank. We’ll also focus on the replacement of your electric water heater’s line of defense against corrosion, the anode rod. Then it’s fill ‘er up, and your maintenance in done.

  • Flushing the Hot Water Tank.  After testing the T&P (temperature and pressure relief) Valve, the next thing to do is to flush the HWT from out of its drain valve. 

 HWT Drain Valve

Turn off the power supply to the tank. Then simply hook a hose to the drain, run the hose to a safe draining area, (avoid plants/grass) and open the drain on the tank until it flushes clean.   If you’re on city water no more than 5-minutes is usually fine as most water supplies come from reservoirs and/or rivers, and the water is not hard (less than 2 grains of hardness). 

  • If you are on a well the water can be much harder.  Simply put, the raw water contains minerals (rock).  When hard water is heated in your HWT, the heat causes the minerals  to ‘precipitate’ out of solution, fall to the bottom of the tank and build up, making it harder and slower to heat the water, and taking more energy than when clean.  This (picture) HWT was on a well in Arlington, WA. Note the grey granular looking stuff at the bottom; that’s the precipitated rock that was in the water before it was heated.


 Sediment. The results of hard water,minerals, etc

 If you have hard water, flush for 5 or 10 minutes, then turn off the water supply so you can drain the tank completely.  You will likely have to allow air into the HWT by opening a hot valve or two in the house to get the tank completely empty.   Once empty, turn on the water to the HWT with the drain still connected to the hose, turn off the hot faucets you had on to let air in, and keep flushing the HWT for another 10 to 20 minutes, until you get the water to run as clear as you reasonably can. 

  • Checking the Expansion tank.  After flushing the HWT from it’s drain, check to see if the expansion tank is in working condition, (assuming of course the HWT has one).  Our experience is that approx. 80% of all expansion tanks are not installed or sized correctly, and they fail (the bladder blows) within 1 – 2 years.  The picture below shows a normal expansion tank & a ‘cut-away’ tank.


Expansion Tank incl. cutaway

 Expansion tanks are required by both code and common sense on any system that is a ‘Closed’ system; i.e.; any system with some type of check-valve in the supply water that does not allow the water to expand backwards upstream when it is heated and then expands. (Most water meters in western WA. Have check valves in them that won’t allow the water to expand back into the water main. Your local water department can tell you what type of meter your property has.

Note: 50- gallons of 50° F. water becomes about ½ gallon larger when heated to 120° F, and if it has no place to expand into (like the water main out under the street, or the expansion tank), it cracks the glass lining in the HWT the first few times the HWT is fully heated. Then the rusting starts and the tank will leak sooner than later.  Also, the huge pressure fluctuations are very hard on all the plumbing in the whole system.

  • To check the expansion tank…
    • Make sure you know the incoming water pressure (PSI) that this HWT is connected to from step #1. You need to know this in order to ‘Tune’ the expansion tank after you check it to see if the bladder is blown.


Hose Bib with Pressure Gauge

  • With no water pressure on the HWT & the expansion tank, let all the air out of the little air valve on the top of the tank. If you get any water out with the air, the bladder is blown & the expansion tank must be replaced. You may get a few drops of  moisture/condensate. Drops are fine; more than that is not.


Schrader Valve

  • If no water comes out of the valve except a few drips of condensate moisture, the bladder is sound.  With the water pressure off to the HWT and the expansion tank, ‘charge’ the expansion tank with an air pump or air compressor until the air PSI matches the water pressure PSI on the cold water line supplying the tank.  Your expansion tank is now both checked for soundness and ‘Tuned’ to it’s water supply pressure, and if sized right by the installer, will provide maximum room for water expansion.
  • Replacing the Anode Rod.  All tank-style water heaters made of steel (as opposed to stainless steel) have anode rods in them.  They are also called ‘sacrificial rods’ because they are designed to cause the corrosiveness/aggressiveness of the water to ‘attack’ them, rather than the tank itself.  (Even though hot water tanks are ‘glass lined’ tiny cracks develop in the glass lining & the water will rust thru the tank if it gets a chance.)  Our experience in the Pacific Northwest, is that anode rods last an average of 7-years, whether they are on an active hot water tank or simply on a storage tank that doesn’t actually heat the water itself.  They’re difficult to replace. We recommend that you have this done by a licensed plumber.  Below is a picture of a new anode rod next to an 11-year old anode rod inside a hot water tank.  We are pointing to the original, 11-year old rod, that stopped protecting the tank years ago.


Inside HOT WATER TANK: Anode Rod comparison

When all the above is finished, your electric hot water heater can be re-filled.  Open a hot faucet, then fill the hot water tank from the cold supply until it’s completely full, and all the air is forced out of the tank, then out the faucet that is running.  At the beginning of your maintenance, you measured the temperature of the hot water.  Washington state code and law requires that the water be no hotter than 120º F.  This is why….

Water Temperature

Time to Produce a Serious Burn

120º  F.

More than 5 Minutes

125º  F.

1-1/2 to 2 Minutes

130º  F.

About 30 Seconds

135º  F.

About 10 Seconds

140º  F.

Less than 5 Seconds

145º  F.

Less than 3 Seconds

150º  F.

1 to 2 Seconds

155º  F.

About 1 Second


On Contact

Most restaurants use 140º  to 160º F hot water to wash/rinse dishes .

If the temperature needs to be adjusted, open the upper and lower thermostat access panels and adjust as needed.  Then, close the panels, restore power, and your annual maintenance is complete.



As mentioned earlier, this Annual Spring Maintenance is for Electric Water Heaters.  Gas water heaters can be maintained by doing all of the above, and many additional things including burner and chimney vent inspection, gas pressure-test both incoming and on the manifold, proper cleaning of the emergency shut-down system now required by code, carbon monoxide testing in ambient air & in combustion air, and many other things.  Due to the differing specs that apply and the necessary tools required, we recommend licensed plumbers or HVAC/R techs perform maintenance on gas and propane water heaters; both storage tank and tankless styles.

As you can see, maintaining a home’s mechanical systems is not for the faint of heart. Even on something as simple as a standard electric water heater.  Hopefully, you have found this useful and helpful. Bottom line, we  need to maintain all of our mechanical systems, so we can get the safest, most economical return possible for our investments.


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