Nissan micra k 12 no warm flow air inside

Hi, I have a Nissan Micra 1.2 16v of 2005 and the heating does not work.

When I turn the the knob on red (warm) the flow is only lightly warm; the A/C is manual.

I have already checked:

- the liquid of the radiator, ok

- the 2 tubes (in and out) of the radiator of the heating are both properly warm

- the fun works properly in the four speeds

- Fuses are ok

- Thermostat ok

I have read that the blending door/flap could be broken and so not allowing the warm air to come in.

Has anybody got the same problem? it is difficult to fix or replace it?

Any advice would be very appreciated.

Thanks a lot.

Have you recently had a coolant change? as I see it you have two choices either bleed the heater matrix by removing the return pipe for a short while as there may be an air lock restricting the flow of hot coolant from the engine, or if that fails you may need a replacement matrix as it could be blocked or full of deposits. As a last resort try undoing the both pipes to the matrix and reverse flush the matrix with a hose pipe, you may need to fabricate some pipe adapters but this would be easier that replacing the heater matrix.🤔
Also check the mechanics of the heater switch, make sure it opens and closes the lever to the matrix and is not slipping or snapped? :unsure: