Operation; Operating Sequence; Eco (Energy Cut-Off); Temperature Stratification (Stacking) - andrews CSC39 Installation Manual, Operation And Service Manual

OPERATION

When properly installed and adjusted, the heater will require minimal attention. Should it
become necessary to completely drain the heater, follow instructions given in Section 4,
Commissioning.
Whenever the heater is filled with cold water, condensation will form on the storage
vessel surfaces when the burner is lit. This is normal and will disappear when the heater
warms up.

Operating Sequence

1. When the control thermostat senses too-cool water, a signal is sent to the control
sequence unit.
2. When the pilot solenoid opens, gas is allowed to pass to the pilot and simultaneous
ignition begins?
3. When the pilot flame is established, the main gas solenoid is allowed to slowly open
and the main burners or burner is lit.
4. When the control thermostat is satisfied, both pilot and main gas solenoids are closed.

ECO (Energy Cut-Off)

The heater is equipped with an ECO (Energy Cut-Off) device, fitted to the control
thermostat. It is a temperature sensitive switch which opens at high temperature,
shutting off gas to the burners, including the pilot in an overheat condition. When the
water has cooled sufficiently, the manual reset on the ECO needs to be depressed to
allow the heater to be re-lit. If the pilot goes out and is associated with high water
temperature, the ECO is probably operational and the cause of overheating should be
investigated.

Temperature Stratification (Stacking)

When small amounts of hot water are drawn repeatedly, the thermostat responds to each
feed of cold water and activates the main burners. Each time this occurs, more heat may
be put back in the tank than was drawn off. As this continues, water in the upper level
of the tank gets hotter than the thermostat setting. This hotter water does not mix
completely with the cold inlet water, but rises in a 'chimney effect' to the top of the tank.
Many repetitions of this over a short time period results in accumulation of excessively
hot water in the upper part of the tank, even when the thermostat control is within
limits. This is known as stacking.
To counter this condition, an upper thermostat phial is fitted which senses abnormally hot
water and shuts down the main burner until the water cools. Most modern commercial
pipe installations include a circulating pump which keeps hot water moving continuously
throughout the heater. This stabilises temperatures in the water heater tank and
throughout the pipe system.
SECTION 5
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