My 2005 Mini Cooper’s heater often blows really hot air for a minute or so when it starts up. This happens mostly on hot days, and after the car was previously driven.
Is your AC on? There is a lag because the AC compressor has to start working. Cold air takes a minute or so to get into the passenger area. Sounds normal to me. Turn the AC fan control to low for the first minute or so.
Never used to happen like this before - AC is on, but really hot air blows out for two + minutes. Also seems to me that nothing should be blowing out unless the temp is close to what it should be. Way not normal - I’ve never heard of this on another car and never had to turn off the automatic heat/AC control on startup.
Your heater blows hot air? I fail to see the problem. Why are you using the heater on hot days? Please clarify. Does it blow hot air without being turned on? Every time you drive the car, “the car was previously driven.” Please clarify.
You might have the A/C system checked, but it may well be normal. Every car I have had always blows hot air when I turn on the A/C for a few minutes. Have you started parking it in a different (hotter or sunnier spot)?
You could bring it to a good AC shop and have it checked. Note: no quick oil change shop is a good AC shop, or for that matter a good oil change place. Look for a dedicated A/C or Radiator shop.