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Hello and Happy New Year!

We have a 2002 Nissan March (Japanese import) where we're having issues with the heater always being on. The cable control from the dash to the vents is working correctly (cable slides nicely etc) but it seems that the heating unit and pipes feeding the heating unit are still hot. Is this to do with thermostat in the engine bay or some other control valve?

Thanks!

The heater unit will always be fed with water/coolant from the engine and there are control flaps in the housing for the aircon evaporator and heater unit that control the temperature inside the vehicle according to the position of the control knobs.

The chances are that the retaining clip for the control cable has unclipped and when you turn the knob the cable has no effort on the control lever that moves the flap inside the housing. In this case the cable control will feel ok to the user.

Hi, thanks for that information.

I've checked the control cable to the flaps (after removing the dash) and can see that it's connected and working.

So just to clarify, the heater unti inside the car is always going to be hot?

Thanks!

The heater unit will always have a feed of coolant from the engine and if the engine coolant temperature is hot then yes the heater unit will also be hot. The flaps inside the housing shut the heater off when you turn the control knob to cool.

You should move the lever on the housing manually, with the heater cable disconnected, to check if the lever is moving properly to completely shut the flap.

If you struggle then it's best to get a mechanic to have a look at the problem as you could easily damage a part that could require the complete housing to need replacing - which is costly.

Great - thank you for your advice :-)