andrews RSC 150 Installation And Operation Manual page 20

OPERATION
When properly installed and adjusted the Heater will require the minimum of attention.
Should it become necessary to completely drain the heater, close the cold water inlet
valve, open a hot water tap to allow air to enter the system. Fit a suitable hose to the
drain cock and open.
Whenever the Heater is filled with cold water, condensation will form on the cold storage
vessel surfaces when the burner is lit. Condensation is normal and does not indicate a
leak. It will disappear when the storage vessel becomes heated.
The gas control fitted to this heater has a built in limit thermostat (ECO). In case of high
water temperature the gas supply will be automatically shut off. The reason for such a
high temperature must be investigated and corrected before the heater is relit.
The gas control is fitted with a recycling type ECO, this means that once the water
temperature has cooled sufficiently the ECO circuit will close and allow the heater to be
relit. If the gas control has to be changed it must be replaced with an identical model
having the same code number.
1. When the thermostat senses too-cool water, a signal is sent to the control sequence unit.
2. The pilot solenoid coil is energised and thus allowed to open. Gas is allowed to pass to
the pilot and ignition begins.
3. When the pilot flame is established, the main gas solenoid is energised and allowed to
open and the main burner is lit.
4. When the control thermostat is satisfied, both pilot and main gas solenoids are closed.
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.
If in doubt contact Andrews Water Heaters.
SECTION 5
AUTO
IGNITION
UNITS
17