Operating instructions

Failure
Symptom
Probable Cause Remedy
Coolant heater
switches off
automatically
(Fault lock-out)
No combustion after start
or automatic repeat start
Flame extinguishes
during operation
Heater overheats
Vehicle electrical system
voltage too low
Switch off heater momentarily and switch on once
again
Switch off heater momentarily and switch on once again
Check coolant lines for obstructions, closed valves and kinks.
Check coolant level. Allow heater to cool down, reset over heat
limiter, switch off heater momentarily and switch on once again
Charge battery
Switch off heater momentarily and switch on once
again
Heater expels black
fumes from exhaust
Combustion air and/or
exhaust ducting blocked
Check combustion and exhaust ducting for obstructions
Table 601: General Failure Symptoms
5.3 Operational Failure Symptoms
Failure Symptom Probable Cause Check and Correct
No Function -Electrical wiring, fuses
-Defective control unit
-Fuses
-Battery connections
-Positive on A5, negative on A3,
positive “ON” signal on A1
-Replace control unit
1X Flash (F 01)
No start no combustion after start
and repeat start
-Fuel system
-Combustion air
-Burner
-Fuel level
-Type of fuel being used
-Fuel filter
-Fuel line connections (air bubbles in
fuel lines)
-Air intake or exhaust, restricted or
plugged
-Clean burner pilot bores
2X Flashes (F 02)
Flame out during operation
-Fuel supply (shortage of fuel)
-Burner
-Restriction in the fuel system
-Fuel filter
-Fuel line connections (air bubbles in
fuel lines)
-Type of fuel being used
-Clean or replace burner
3X Flashes (F 03)
Low voltage for more than
20 seconds
-Electrical system -Load test batteries
-Corrosion at connections
-Loose connections
602
6 Basic Troubleshooting Thermo 90 S