5 Troubleshooting Thermo 90 S / Thermo 90 ST
502
5.3 Fault indications on fault lock-out
NOTE
If the system is operated with a switch, the nature of the
fault is indicated by a flashing code on an indicator light
during the run-on time of the heater.
After five short signals, count the long flashes.
In the Thermo 90 S heater with a standard clock, the fault
is output on the clock display (see 3.6.3). The following
table can be used accordingly.
Fig. 502 Fault indications on fault lock-out (page 1 of 2)
Fault indication Possible cause Remedy
No function Electrical cabling,
fuses
Check fuses
Check battery connections:
+ on 12 / – on 9 / + on 3, plug X12
(Thermo 90 S)
+ on 12 / – on 9 / + on 3, plug X8
(Thermo 90 ST)
Control unit defective Replace control unit
1 Flashing pulse
(start did not occur)
Fuel system Check fuel level
Check fuel filter
Bleed fuel system
Combustion air/exhaust line Check combustion air/exhaust line for
foreign bodies and clean if necessary
Burner Clean burner and change if necessary
2 Flashing pulses
(flame failure during burner
operation)
Fuel supply Check fuel level
Check fuel filter
Bleed fuel system
Burner Clean burner and change if necessary
3 Flashing pulses
(undervoltage)
Electrical power supply Check battery
Check electrical connections
4 Flashing pulses
(flame monitor continuously
hot)
Flame monitor defective Replace flame monitor
5 Flashing pulses
(flame monitor defective)
Cabling Check cabling for damage, discontinuity and
short-circuit
Flame monitor defective Replace flame monitor
6 Flashing pulses
(temperature sensor
defective)
Cabling Check cabling for damage, discontinuity and
short-circuit
Temperature sensor defective Replace temperature sensor
7 Flashing pulses
(metering pump defective/
(overheating guard circuit
defective)
Coolant circuit Check coolant level
Bleed coolant circuit
Reset temperature limiter
Cabling Check cabling for damage, discontinuity and
short-circuit
Metering pump defective Replace metering pump
8 Flashing pulses
(combustion air fan
defective)
Cabling Check cabling for damage, discontinuity and
short-circuit
Combustion air fan defective Replace combustion air fan
