Operation; Auto Ignition Units - andrews RSC 150 Installation And Service Manual

5

Operation

5 Operation
5.1

Auto ignition units

22
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.
Note
If in doubt contact Andrews Water Heaters.
E104 Issue 2 14/07/16