Heater does not work

First check the heater air and combustion air blowers visually to determine that they are operating, then check that the fuel pump is working (the pump ticks audibly). If these units are working, check the glow-spark plug (at the same time check whether fuel is pumped into the heater - check at exhaust pipe).

Defective units should be repaired or replaced with new ones.

If this check shows that the heater is not working, check as follows:

Step 1: Mechanical inspection

Check all heating system units and warm air ducts as well as electrical connections for tightness, check exhaust system for damages

Possible defect Remedy
Reduction in exhaust pipe cross section, exhaust pipes and warm air ducts loose Replace damaged parts with new ones
Loose connection in electrical system Tighten loose push-on connections

Step 2: Main fuse

Check 16 Amp main fuse (no current at relay terminal E)

Possible defect Remedy
Short circuit in electrical system Disconnect cables at relay terminals G, E and F. Install new fuse and reconnect cables individually. If fuse blows, check appropriate cables and units and replace if necessary.

Step 3: Overheating fuse

Check 8 Amp overheating fuse

Possible defect Remedy
Overheating due to failure of heater air blower Check heater air blower
Warm air duct blocked (fresh air and defroster vents or outlets in footwell) Check warm air ducts for blockage
Heater flaps closed Adjust heater flap cable

Step 4: Battery

Test battery voltage

Possible defect Remedy
Voltage too low Charge battery (if necessary start vehicle engine)

Step 5: Fuel pump


Disconnect cables at fuel pump so no fuel is delivered during further tests

Step 6: Relay

Disconnect cable at relay of terminal A, then reconnect cable (relay must be heard to work)

Possible defect Remedy
Safety switch has cut in because of defect in fuel supply or ignition system Switch safety switch back on and eliminate defect if necessary
Temperature control switch defective (open circuit) Check temperature regulating switch and temperature sensor
Contact on heater flap lever does not close Check contact

Step 7: Relay voltage

Measure voltage at relay terminals C, D and G

Possible defect Remedy
If there is no voltage, relay is defective (open circuit) Install new relay

Step 8: Heater air blower

Check whether heater air blower forces air into vehicle interior

Possible defect Remedy
Blower fan loose Check heater air blower and repair or replace if necessary (

Step 9: Heater air blower speed

Disconnect cables on ignition coil and connect tachometer (Chapter 1.3), then read off speed (6400-7100 rpm at nominal voltage).

Possible defect Remedy
If speed too low, voltage drop in plug for combustion air blower motor or in relay Test and install new relay if necessary
Armature burnt, brushes worn Repair combustion air blower motor
Bearing or winding damage Replace combustion air blower motor

Step 10: Glow/spark plug

Remove 16 Amp fuse. Push heater flap lever fully forward, warning lamp goes out. Unscrew glow-spark plug. Reconnect cables, install fuse and operate heater flap lever. Sparks must jump between electrode and casing and glow element must glow.

Possible defect Remedy
Thermo switch defective (no current, glow time too short) Install new thermo switch
Glow element open Install new glow-spark plug
Glow-spark plug dirty Clean glow-spark plug
Ignition contact breaker defective or maladjusted Adjust contact breaker or replace if necessary
Ignition cable or coil defective Test ignition system and install new parts if necessary

Step 11: Fuel pump

Turn heater off, remove pump and measure capacity

Possible defect Remedy
Contact breaker defective or maladjusted Adjust contact breaker or replace if necessary
Open circuit in pump winding Install new pump
Maladjustment Correct adjustment
Fuel hoses, filter or strainer blocked Clean parts
Valve does not open Replace fuel check valve. Readjust delivery capacity