A.O. Smith FMD 40 Manuale Utente

24

Each water heater contains at least one anode rod, which will 

slowly deplete (due to electrolysis) prolonging the life of the water 

heater by protecting the glass-lined tank from corrosion. Adverse 

water quality, hotter water temperatures, high hot water usage, and 

water softening methods can increase the rate of anode rod deple-

tion. Once the anode rod is depleted, the tank will start to corrode, 

eventually developing a leak. 

Certain water conditions will cause a reaction between the anode 

rod and the water. The most common complaint associated with 

the anode rod is a “rotten egg smell” produced from the presence 

of hydrogen sulfi de gas dissolved in the water. IMPORTANT: Do 

not remove this rod permanently as it will void any warranties. 

The parts list includes a special anode rod that can be ordered if 

water odor or discoloration occurs. NOTE: This rod may reduce 

but not eliminate water odor problems. The water supply system 

may require special fi ltration equipment from a water conditioning 

company to successfully eliminate all water odor problems.

Artifi cially softened water is exceedingly corrosive because the 

process substitutes sodium ions for magnesium and calcium ions. 

The use of a water softener may decrease the life of the water 

heater tank.

The anode rod should be removed from the water heater tank every 

3 years for inspection. NOTE: artifi cially softened water requires the 

anode rod to be inspected annually.

 The following are typical (but not all) signs of a depleted anode rod:
 

• 

The majority of the rods diameter is less than 3/8”.

 •  Signifi cant sections of the support wire (approx. 1/3 or   

 

more of the anode rod’s length) are visible.

If the anode rod show signs of either or both it should be replaced. 

NOTE: Whether re-installing or replacing the anode rod, check 

for any leaks and immediately correct if 

found.

In replacing the anode:

Turn off gas supply to the water heater.

1. 

Shut off the water supply and open a 

2. 

nearby hot water faucet to depressurize 

the water tank.
Drain approximately 5 gallons of water 

3. 

from tank (Refer to “Draining” for proper 

procedures). Close drain valve.
Remove old anode rod.

4. 

Use Teflon® tape or approved pipe 

5. 

sealant on threads and install new 

anode rod.
Turn on water supply and open nearby 

6. 

hot water faucet to purge air from 

water system. Check for any leaks and 

immediately correct any if found.

Restart the water heater as directed under 

“Operating Your Water weater.” See the Repair Parts Illustration for 
anode rod location.

                      

The temperature-pressure relief valve must be manually operated at 
least once a year.
When checking the temperature-pressure relief valve operation, make 
sure that (1) no one is in front of or around the outlet of the temperature-
pressure relief valve discharge line, and (2) that the water discharge 
will not cause any property damage, as the water may be extremely 
hot, see Figure 39.

If after manually operating the valve, it fails to completely reset and 
continues to release water, immediately close the cold water inlet 
to the water heater, follow the draining instructions, and replace the 
temperature-pressure relief valve with a new one.
If the temperature-pressure relief valve on the appliance weeps or 
discharges periodically, this may be due to thermal expansion.  You 
may have a check valve installed in the water line or a water meter 
with a check valve.  Consult your local water supplier or service agency 
for  further information.  Do not plug the temperature-pressure relief 
valve.

The water heater should be drained if being shut down during freezing 
temperatures.  Also periodic draining and cleaning of sediment from 
the tank may be necessary.
1.  Turn the gas control knob to the “OFF” position.
2.  OPEN nearby hot water faucets and leave open until the water is 

no longer hot.  

3.  CLOSE the cold water inlet valve to the water heater.
4.  Connect a hose to the drain valve and terminate to an adequate 

drain or outdoors.

5.  OPEN the water heater drain valve to allow for tank draining.
NOTE: If the water heater is going to be shut down and drained for 
an extended period, the drain valve should be left open with hose 
connected allowing water to terminate to an adequate drain.