Draining And Flushing; Sediment Removal; Lime Scale Removal - A.O. Smith 300 Series Instruction Manual

DRAINING AND FLUSHING

It is recommended that the water heater storage tank be drained and
flushed every 6 months to reduce sediment buildup. The water heater
should be drained if being shut down during freezing temperatures.
See Figure 3 (page 10) and Figure 4 (page 11) for the location
of the water heater components described below.
TO DRAIN THE WATER HEATER STORAGE TANK:
Turn off the electrical supply to the water heater.
1.
Turn off the gas supply at the Main Gas Shutoff Valve if the water
2.
heater is going to be shut down for an extended period.
Ensure the cold water inlet valve is open.
3.
Open a nearby hot water faucet and let the water run until the
4.
water is no longer hot.
Close the cold water inlet valve to the water heater.
5.
Connect a hose to the water heater drain valve and terminate it
6.
to an adequate drain.
Open the water heater drain valve and allow all the water to drain
7.
from the storage tank.
Close the water heater drain valve when all water in the storage
8.
tank has drained.
Close the hot water faucet opened in Step 4.
9.
10. If the water heater is going to be shut down for an extended
period, the drain valve should be left open.
TO FLUSH THE WATER HEATER STORAGE TANK:
Turn off the electrical supply to the water heater.
1.
Ensure the cold water inlet valve is open.
2.
Explosion Hazard
Temperature-Pressure Relief Valve
must comply with ANSI Z21.22-
CSA 4.4 and ASME code.
Properly sized temperature-
pressure relief valve must be
installed in opening provided.
Can result in overheating and
excessive tank pressure.
Can cause serious injury or death.
Burn hazard.
Hot water discharge.
Keep clear of Temperature-
Pressure Relief Valve
discharge outlet.
Open a nearby hot water faucet and let the water run until the
3.
water is no longer hot. Then close the hot water faucet.
Connect a hose to the drain valve and terminate it to an adequate
4.
drain.
Ensure the drain hose is secured before and during the entire
5.
flushing procedure. Flushing is performed with system water
pressure applied to the water heater.
Open the water heater drain valve to flush the storage tank.
6.
Flush the water heater storage tank to remove sediment and
7.
allow the water to flow until it runs clean.
Close the water heater drain valve when flushing is completed.
8.
Remove the drain hose.
9.
10. Fill the water heater. See Filling the Water Heater (page 50).
11. Turn on the electrical supply to place the water heater back in
operation.
12. Allow the water heater to complete several heating cycles to
ensure it is operating properly.

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

When water is heated dissolved minerals in the water such as
calcium and magnesium carbonate (lime scale) become less soluble.
As the water temperature rises these minerals will precipitate or "fall
out" of solution.
The amount of lime scale 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.
Water hardness also affects lime scale accumulation. With the
temperature and usage being the same, hard water will release
more lime scale than softer water.
Lime scale reduces heating efficiency as it accumulates inside a
water heater. Heating transfer surfaces become coated with lime
scale deposits which increases fuel costs to operate the water heater.
Lime scale deposits can also cause rumbling and pounding noises
as air molecules trapped in the lime scale escape when heated. Lime
scale accumulation also reduces the life span of water heaters. For
these reasons a regular schedule for deliming should be set up.
The depth of lime accumulation in the bottom of the water heater
should be measured periodically. Inspect by removing the cleanout
cover once every 6 months at first. Deliming maintenance should
then be performed based on the time it takes for 1 inch (2.5 cm) of
lime to accumulate in the bottom of the water heater.
CHEMICAL LIME SCALE REMOVAL
To dissolve and remove more stubborn lime scale deposits, UN-
® Professional Delimer should be used.
LIME
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. Hydrochloric base acids must not
be used to delime the water heaters covered in this manual.
Follow the instructions on the UN-LIME
55
® to delime the water heater.