Insufficient heat output

Step 1: Fuel pump

Check delivery quantity of fuel pump.

Possible defect


Delivery quantity too small

Adjust delivery quantity

Filter blocked

Clean filter

Strainer dirty

Clean strainer

Fuel check valve blocked

Install new fuel check valve

Step 2: Temperature regulating system

Check temperature regulation.

Possible defect


Check temperature sensor and temperature regulating switch

Replace temperature sensor

Step 3: Engine heat exchanger

Check adjustment of heater flaps on engine heat exchanger.

Possible defect


Bowden cable adjustment not correct


Step 4: Engine cooling air housing

Non-return flaps in engine cooling air housing stiff or jammed.

Possible defect


Not installed correctly

Remove cooling air fan and check flaps. replace if necessary.