Hello and Welcome to justanswer...

The usual fault / cause of this is either the cable has become detached from the heat ..hot / control button - at the back of it...or on the heater box where it attaches so while you operate the button, its not actually doing anything - controlling the air flow.

The best thing to do is access the cables where they connect under the dash to the heater --you can do looking up under the dash in the middle - locate the cable...operate the control button and watch to see whats happening.

You should see either the cable clip has come off - or instead of just the inner cable moving which it should, the whole cable moves - meaning the clip has come off ( look at the other cable to get the idea ).. or the cable has seized. If nothing is happening - the fault is at the button end - the panel will have to be removed then to check that out.

Other than that , the fault can be the blend doors themselves / flaps not working or broken on the heater motor - or, simply the pipes have come off up under the dash to the vents.

So work through checking as above to trace and cure this fault.

Im very pleased to have helped you - Let me know if I can help anymore...

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Kind Rgds - MIKE