A.O. Smith 400A - Manual (Page 28)

8
FLUSHING
1. Turn off the heater electrical disconnect switch.
2. Open the drain valve and allow water to flow until it runs clean.
3. Close the drain valve when finished flushing.
4. Turn on the heater electrical disconnect switch.
DRAINING
The heater must be drained if it is to be shut down and exposed to
freezing temperatures. Maintenance and service procedures may
also require draining the heater.
1. Turn off the heater electrical disconnect switch.
2. Close the cold water inlet valve to heater.
3. Open a nearby hot water faucet to vent the system.
4. Open the heater drain valve.
5. If the heater is being drained for an extended shutdown, it is
suggested the drain valve be left open during this period.
• Follow FILLING instructions when restoring hot water service.
SEDIMENT REMOVAL
Waterborne impurities consist of the particles of soil and sand which
settle out and form a layer of sediment on the bottom of the tank.
For convenience, sediment removal and lime scale removal should
be performed at the same time.
LIME SCALE REMOVAL
The amount of calcium carbonate (lime) released from water is
in direct proportion to water temperature and usage. The higher
the water temperature or water usage, the more lime deposits are
dropped out of the water. This is the lime scale which forms in pipes,
heaters and on cooking utensils.
Lime accumulation not only reduces the life of the equipment but also
reduces efficiency of the heater and increases fuel consumption.
The usage of water softening equipment greatly reduces the
hardness of the water. However, this equipment does not always
remove all of the hardness (lime). For this reason it is recommended
that a regular schedule for deliming be maintained.
The depth of lime buildup should be measured periodically. Heaters
will have about 3" (7.6cm) of lime buildup when the level of lime has
reached the bottom of the cleanout opening or about 1" (2.5cm) of
lime buildup if it has reached the drain valve opening. A schedule
for deliming should be set up, based on the amount of time it would
take for a 1" (2.5cm) buildup of lime.
Example 1:
Initial inspection shows 1/2" (1.3cm) of lime accumulation.
Therefore, the heater can be delimed once a year.
Example 2 :
Initial inspection shows 2" (5cm) of lime accumulation. Therefore,
the heater should be delimed every 3 months.
Sediment and lime scale removal may be accomplished through
the cleanout opening furnished on the heater, see Figure 24. The
heater must be drained, see DRAINING, before removing cleanout
cover on tank.
FIGURE 24.
To dissolve and remove the more stubborn mineral deposits,
A.O. Smith UN•LIME® Professional Delimer should be used. NOTE:
UN•LIME is not available in Canada. Please call Customer Service
at 1-800-265-8520 for approved alternatives.
A.O. Smith UN•LIME® Professional Delimer is an easy to handle
patented food grade acid formulated specifically for lime scale
removal from all types of water using equipment. Available in 1
gallon (3.8L) (part no. 4763) and 5 gallon (19L) (part no. 4813)
sizes. Hydrochloric base acids are not recommended for use on
glass-lined tanks.
A.O. Smith Form No. 4800 Rev. 8, entitled “Why, When and How”,
describes tank cleaning methods and materials. UN•LIME and
the booklet may be obtained through your A.O. Smith dealer or
distributor.
The cleanout opening is shown in Figure 24. To clean heater through
cleanout opening, proceed as follow:
1. Turn off water inlet valve, the heater electrical disconnect switch
and open drain valve.
2. Remove outer cover plate from lower side of heater jacket.
3. Remove cover from cleanout opening.
4. Remove lime, scale or sediment using care not to damage the
glass-lining.
5. Inspect cleanout plate gasket: If new gasket is required, replace
with A. O. Smith part no. 99038.
6. Install cleanout plate. Be sure to draw plate up tight by tightening
screws securely.
7. Close drain valve, open water inlet line and turn on the power
burner electrical disconnect switch.
8. Check for water leakage.
9. Replace outer jacket cover plate.