401
Thermo G
4 Heater functions
4
Heater functions
4.1
General heater functionality
description
The heater function is based on the principle of the low-
pressure gas burner and is controlled by a micro
processor. At the same time the integrated control unit
takes over all monitoring functions.
An electronically controlled motor drives a fan which
sucks in combustion air and gas as fuel. Both are mixed
in a mixing chamber. The gas-air mixture is then fed into
the combustion chamber of the heater and burned there.
The hot exhaust gases flow through a heat exchanger and
thus provide heat to the water circuit connected to the
heater.
The heater works intermittently, that means the gas
burner is switched on and off according to the heat
demand in the water cycle.
The ignition of the gas-air mixture takes place in the
combustion chamber by high-voltage ignition sparks.
The flame recognition is carried out by an in the ZF-
module (electronic ignition unit) integrated flame guard.
The principle is based on the measurement of the ionisa-
tion current through the flame.
Depending on the equipment, the heater is switched on
and off using a
•
digital timer
•
switch
•
or climate control.
During heating operation the burner is automatically swit-
ched on and off. For regulation a temperature sensor is
installed in the coolant outlet of the heat exchanger. The
heater is switched on, when the temperature falls short of
a lower temperature threshold (72°C), and is switched off,
if the upper temperature threshold is reached (82°C). A
distinction between parking heating and auxiliary heating
mode does not exists.
For overheating protection of the heater the switching
thresholds are modified by the control unit, if specified
temperature gradients are exceeded (gradient evalua-
tion).
An operating display is available for monitoring the opera-
ting status. The operating display is also used to output
error messages in flash code.
