Flushing; Draining; Sediment Removal; Lime Scale Removal - A.O. Smith BTH 120-250(A) Installation & Operating Instructions Manual

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 25. The heater must
be drained, see DRAINING, before removing cleanout cover on tank.
To dissolve and remove the more stubborn mineral deposits, A.O. Smith
UN•LIME® Professional Delimer should be used.
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, 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 25. 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.

ANODE INSPECTION AND REPLACEMENT

This water heater is equipped with multiple sacrificial anodes. Anodes
protect the glass-lined tank from corrosion by sacrificing themselves
through electrolysis. When the anode material is consumed, there is no
more protection and corrosion of the tank accelerates
Inspection of the anode every 6 to 12 months allows you to identify a
spent anode and replace it. Replace the anode when its diameter is
3/8" (1cm) of an inch, or annually which ever is first. Aggressive, very
hot and softened water causes rapid consumption of the anode requiring
frequent inspections. Anodes are available from your distributor or
A.O. Smith.
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FIGURE 25