No heat in the cab
Can I keep driving?
Check the engine temperature gauge and the coolant level first. If both are normal, the truck can run; book a bay. If either is off, read the coolant page linked below before you drive on.
Do this first
- Check the gauge and the tank. If the engine is not reaching normal operating temperature, a stuck-open thermostat is giving you an engine that never gets warm enough to heat anything, and that costs fuel and wear too. If the coolant level is low, the heater core sits high and is the first thing to run dry. Top up only when cool.
- Feel the heater hoses. With the engine warm and the heat on, both hoses at the firewall should be hot. Both cold means coolant is not reaching the core: a closed valve, an air lock, or a plugged core. One hot and one cold means coolant is reaching it but not flowing through; usually a plugged core. Both hot and no heat in the cab means the problem is on the air side, a blend door, a control, or the fan.
- Check the blower and the controls. Does the fan run on all speeds? Does the temperature control move anything? A blend door actuator that has failed is the most common no-heat on newer cabs with automatic climate control and it has nothing to do with coolant.
What it usually costs and how long it takes
The air side is cheaper than the coolant side, and both are cheaper than the bunk heater:
- Blend door actuator, control head or blower resistor. Small parts; the labor depends on how much dash has to come out.
- Heater control valve or an air lock. Quick at a shop that knows the truck; a proper coolant bleed is the whole fix for a lot of no-heat calls.
- Plugged heater core. Flushing sometimes works; replacement means dash out, which is the expensive version.
- Thermostat. Moderate. Fixing it also fixes the fuel economy that went with it.
- Diesel bunk heater or APU. Its own fuel pump, glow plug and controller. Serviced by shops that list APU work, and the brand matters.
Where to get it fixed
Cities with the most shops listing HVAC and APU work:
Frequently Asked Questions
The heat works at highway speed but not at idle.
That is a coolant-flow symptom: at idle the water pump turns slowly and a marginal system, low coolant, a partly plugged core or an air pocket, cannot push enough hot coolant through the core. It is also a common early sign of a water pump on its way out.
The engine temperature never gets to normal and there is no heat.
A thermostat stuck open. The engine runs cold, the heater has nothing hot to work with, and fuel economy drops. Not urgent, but it does not fix itself.
The bunk heater quit but the cab heat is fine.
Different system. Diesel-fired bunk heaters have their own fuel pickup, pump, glow plug and controller, and the most common faults are a fuel pickup that is above the fuel level, a failed glow plug, or a controller fault code. Note the code on the heater's display; shops that service that brand will ask for it.
Can an air lock really stop the heat?
Yes, and it is one of the most common reasons a truck comes back with no heat right after cooling-system work. Coolant has to be bled with the cab heater on and the engine at temperature; a shop that skips that step sends you out with a cold cab.
Is it dangerous to drive without heat?
Cold is a comfort problem until the windshield fogs or ices, and then it is a visibility problem. If the defroster cannot keep the glass clear, you stop. In winter, no heat also means your sleeper is not a place you can spend a night, which is its own hours-of-service problem.
Why does the shop want to pressure-test the cooling system for a heater complaint?
Because a heater core that is not getting coolant is often a system that is losing coolant somewhere else, and the shop would rather find that leak now than have the engine find it on a grade.
- The heat works at highway speed but not at idle.
- That is a coolant-flow symptom: at idle the water pump turns slowly and a marginal system, low coolant, a partly plugged core or an air pocket, cannot push enough hot coolant through the core. It is also a common early sign of a water pump on its way out.
- The engine temperature never gets to normal and there is no heat.
- A thermostat stuck open. The engine runs cold, the heater has nothing hot to work with, and fuel economy drops. Not urgent, but it does not fix itself.
- The bunk heater quit but the cab heat is fine.
- Different system. Diesel-fired bunk heaters have their own fuel pickup, pump, glow plug and controller, and the most common faults are a fuel pickup that is above the fuel level, a failed glow plug, or a controller fault code. Note the code on the heater's display; shops that service that brand will ask for it.
- Can an air lock really stop the heat?
- Yes, and it is one of the most common reasons a truck comes back with no heat right after cooling-system work. Coolant has to be bled with the cab heater on and the engine at temperature; a shop that skips that step sends you out with a cold cab.
- Is it dangerous to drive without heat?
- Cold is a comfort problem until the windshield fogs or ices, and then it is a visibility problem. If the defroster cannot keep the glass clear, you stop. In winter, no heat also means your sleeper is not a place you can spend a night, which is its own hours-of-service problem.
- Why does the shop want to pressure-test the cooling system for a heater complaint?
- Because a heater core that is not getting coolant is often a system that is losing coolant somewhere else, and the shop would rather find that leak now than have the engine find it on a grade.
This page is general guidance for professional drivers and is not a diagnosis of your truck. Never open a pressurized cooling system while it is hot. Shop listings are provided by Trucker Path users and the businesses themselves; availability and pricing are confirmed by the shop, not by Trucker Path.