Cooling
Cab Heater Not Working — Common Causes in Vans
A failed cab heater is often caused by low coolant, a stuck thermostat, a faulty heater blower motor, or a blocked heater matrix.
When the cab heater blows cold air despite the temperature setting being on hot, the issue is usually coolant-related. Low coolant level means there is not enough hot coolant flowing through the heater matrix. A stuck-open thermostat prevents the engine from reaching normal operating temperature, so the coolant never gets hot enough. If the blower motor works but the air is cold, the heater matrix may be blocked internally by sludge or debris. If no air comes out at all, the blower motor or resistor pack has failed. A simple check of coolant level and engine operating temperature can diagnose most heater faults quickly.
Key takeaways
- Low coolant level is the most common cause of a heater blowing cold
- A stuck-open thermostat prevents the engine from reaching operating temperature
- A blower motor that works but blows cold air usually means a blocked heater matrix
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