Hiflo And Standard Range Auto Ignition; Auto Ignition Units, Operating Sequence. Hiflo And Standard Range; Eco (Energy Cut-Off); Temperature Stratification (Stacking) - andrews 24/39 Installation And Service Manual

5 Operation
5.3

HIflo and Standard Range Auto ignition

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5.3.1 Auto ignition units, operating sequence. Hi-
Flo and standard range
1. When the control thermostat senses too-cool water, a signal
is sent to the control sequence unit.
2. The flue damper unit is de-energised and thus allowed to
open. (HIflo only).
3. When the flue damper is fully open, gas is allowed to pass to
the pilot and simultaneous ignition begins. (HIflo only).
4. When the pilot flame is established, the main gas solenoid is
allowed to slowly open and the main burners or burner is lit.
5. When the control thermostat is satisfied, both pilot and main
gas solenoids are closed.
6. The damper motor is energised and the damper closes. (Hi-
Flo only).
5.3.2

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. 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.
5.3.3

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 result 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 (not
on Model 32/143) 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.
Issue 2 14/07/16