402
Thermo G
4 Heater functions
4.2
Operational heater sequence
4.2.1 Switching on and start
When switched on, the operating display is illuminated,
the control unit starts controlled operation and checks the
coolant temperature.
If the coolant temperature is below the upper temperature
threshold, the initial cycle starts. This takes approx.
15 seconds, if the coolant temperature is below -20°C
approx. 40 seconds.
The initial cycle is used to start the combustion air motor
and to query the flame monitoring. By the combustion air
motor, the heat exchanger is flushed and at the same time
a negative pressure to the gas pressure regulator is
generated.
The solenoid valve 1 at the gas pressure regulator is swit-
ched on (open), so that the gas can flow from the gas tank
into the gas pressure regulator.
Then, during the pre-ignition the electronic ignition unit is
turned on to check its function, and to ensure an imme-
diate ignition when the gas flows in.
Approximately 1 second later the solenoid valve 2 at the
gas pressure regulator is turned on (open) and now gas
can sucked in.
With the opening of the solenoid valve 2, the safety time
begins (10 s).
When the gas-air mixture the combustion chamber has
reached, it is ignited by the activated electronic ignition
unit.
When the ignition of the gas-air mixture was successful,
the flame guard detects the flame, and the system state
will change to flame stabilization.
The state flame stabilization is used to stabilize the
combustion and ends with the query / decision of the
flame guard "flame". If yes, the system changes into the
heating mode.
NOTE:
If during the start the main switch is turned off, or the water
temperature rises above the upper temperature threshold,
or a fault is detected, the system switches into the purge
cycle.
4.2.2 Heating operation
After the flame is stabilized, the heater is in controlled
operation.
The operation indication, the circulating pump, the
combustion air motor, the solenoid valves 1 and 2 at the
gas pressure regulator and the flame guard are active.
Once the upper switching threshold is exceeded, the
heating operation is terminated and the purge cycle is
initiated. The solenoid valves at the gas pressure regu-
lator are closed, the flame extinguishes, but the combus-
tion air fan and the circulating pump continue running.
Fig. 401 Operational sequence
*
Coolant temperature below -20°C 40 seconds, otherwise 15 seconds, plus 0.3 seconds delayed switching of the combustion air motor and circulating pump
**
On/Off depending on T
Process
Signals
Main switch
off
on
off
Coolant temperature
T > T_min T < T_min
T >= T_max
T < T_min
T >= T_max
T < T_min
Fla
m
e
ge
ne
ra
tion
Fla
m
e
ge
ne
ra
tion
Fla
m
e
ge
ne
ra
tion
Actuators
Operating display
Combustion air motor
Circulating pump
Electronic ignition unit
Solenoid valve 1
Solenoid valve 2
ERH **
Time in s
3 37/12* 1
9
1
...
5
115
3 37/12* 1
9
1
...
5
115
12 37/12* 1
9
1
...
5 115
State
Ready
to s
tar
t
In
itia
l c
ycl
e
with lig
ht
chec
k
Pr
e-
ign
iti
on
Igni
tion
Stab
iliz
atio
n
Pur
ge
cy
cl
e 1 w
ith s
afe
ty p
er
iod
Pur
ge cy
cl
e
2
In
itia
l c
ycl
e
with lig
ht
chec
k
Pr
e-
ign
iti
on
Igni
tion
Stab
iliz
atio
n
Pur
ge
cy
cl
e 1 w
ith s
afe
ty p
er
iod
Pur
ge cy
cl
e
2
In
itia
l c
ycl
e
with lig
ht
chec
k
Pr
e-
ign
iti
on
Igni
tion
Stab
iliz
atio
n
Pur
ge
cy
cl
e 1 w
ith s
afe
ty p
er
iod
Pur
ge cy
cl
e
2
Off
Standby
Start
Heating
Purge
cycle
Standby
Start
Heating
Purge
cycle
Standby
Start
Heating
Purge
cycle
Off
