A.O. Smith ADM - 80 - Manual (Page 13)

Instruction manual ADM 13
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2.4.2 Water temperature protection
By means of the frost, high-limit and safety thermostats, the burner control
monitors three temperatures that are important for safety. The table explains the
working principle of the thermostats with sensors.
Temperature protection
2.4.3 Flue gas backflow safeguard
The flue gases are discharged to the outside via the draught diverter (33) and
the flue (22). To prevent the flue gases from flowing back into the boiler room,
the discharge ducting is monitored by a feature called the Thermal Reflux
Safeguard (TRS). This uses a flue gas thermostat (37) with a flue gas
thermostat sensor (34) that are located in the draught diverter. Under normal
circumstances this sensor will register the ambient temperature.
However, if the chimney is not drawing sufficiently (for example, due to a
blockage in the chimney), the flue gases will 'reflux' and flow back past the flue
gas thermostat sensor. The sensor will then detect an excessive temperature
and the flue gas thermostat will open. The demand will cease, and the burner
control will immediately stop the heating cycle. The flue gas thermostat will also
lock out. It must be manually reset before the appliance can resume operation .
2.4.4 Flame probe
To ensure that no gas can flow when there is no combustion, the water heater
is fitted with a flame probe (21). The burner control uses the ionisation-detecting
properties of this probe for flame detection. The burner control closes the gas
valve the instant it determines that there is a gas flow but no flame is present.
2.5 Safety of the
installation
In addition to the appliance's standard built-in safety monitoring, the appliance
must also be protected by an expansion vessel, expansion valve, pressure
reducing valve, non-return valve and a T&P valve.
The use of an expansion vessel, expansion valve and/or pressure reducing
valve depends on the type of installation: unvented or vented.
2.5.1 Inlet combination and pressure-reducing valve
In addition to the appliance's standard built-in safety monitoring, the appliance
must also be protected by an expansion vessel, expansion valve, pressure
reducing valve, non-return valve and a T&P valve.
The use of an expansion vessel, expansion valve and/or pressure reducing
valve depends on the type of installation: unvented or vented.
Protection Description
Frost thermostat When the frost thermostat sensor (46) measures a temperature of 20°C or
less, the heating cycle (2.3 "The appliance's heating cycle") will start.
High-limit thermostat When the high-limit thermostat sensor (39) measures a temperature higher
than 84°C, the high-limit thermostat will open. The heat demand is terminated
and the burner control halts the heating cycle until the high-limit thermostats
close once more. At that moment the burner control will reset the appliance and
the heating cycle will restart. The high-limit safeguard serves to prevent
overheating and/or excessive formation of scale in the appliance.
Safety thermostat When the safety thermostat sensor (38) measures a temperature higher than
93°C, the safety thermostat will open. The heat demand is terminated and the
burner control will immediately halt the heating cycle. The burner control will go
into a lockout error state. This must be manually reset before the appliance can
resume operation.