Thermo 90 S / Thermo 90 ST 5 Troubleshooting
501
5 Troubleshooting
5.1 General
This section describes how to identify and remedy faults
on the Thermo 90 S und Thermo 90 ST heater.
CAUTION
Troubleshooting work demands precise knowledge of the
structure and theory of operation of the various
components and must be carried out by trained personnel
only.
If in doubt, refer to sections 2 and 3 for a description of
how the functions interact.
CAUTION
As a rule, fault detection is restricted to the localisation of
defective components.
The following potential sources of malfunctions are not
taken into account and should always be checked so that
they can then be excluded as the cause of the particular
fault:
• Corroded plugs
• Loose plug contacts
• Poor crimp contacts on plugs
• Corroded cables and fuses
• Corroded battery terminals
• Impermissibly high ambient temperature
Conduct a function test in the vehicle after rectifying each
fault; switch the heater off and back on again first.
5.2 General fault indications
The following table (Fig. 501) lists the possible general
fault indications.
Fig. 501 General fault indications
NOTE
In many cases, the burner may be one possible cause.
Perform a visual check in accordance with 5.4.
Fault indication Possible cause Remedy
Heater switches off
automatically
No combustion after start and
restart
Control unit enters fault lock-out status.
Switch the heater off and back on again.
Flame extinguishes during
operation
Contact a Webasto service centre if heater
operation does not start again
Heater overheats due to lack/
loss of coolant
Top up coolant.
After the unit has cooled down, press the
button of the temperature limiter before
switching on or fit a new temperature limiter
Voltage failure
longer than 20 seconds
Check fuses, plug connectors and charge
condition of the battery
Switch off by temperature limiter After the unit has cooled down,
press the button of the temperature limiter
before switching on or fit a new temperature
limiter
No flame recognition on start Check flame monitor and connections
