[ariver20]

I have a 2024 BMW X1. I turned the heating up to the maximum for about 10 minutes because I was really cold.

However, an unpleasant smell started coming out, so I turned the heating off.

Now, when I turn the heating back on, the unpleasant smell sometimes reappears. What could be the issue? What should I do about this?

[J-RO]

Check under the hood and see if there are any dead animals in there.

[ariver20]

No dead animals

[kenrok1]

not knowing what kind of unpleasant smell you may get a lot of guesses and suggestions - its always good idea to clean leaf debris out of the inlets under the wiper area and check/replace the cabin air filter. But anything beyond that is probably best left to your service dept

[LondonDubaiX1]

You can get AC cleaner, it’s usually called one shot or something similar and you set it off and shut the doors with the AC on full power and it helps kill any bacteria in the system

[DestinationMoon!]

Do you keep the car inside or out? If outside what's the weather been like? Did you smell anything at lower speeds?

[John27]

As @LondonDubaiX1 says, often smells in heating/air con are from bacteria in the system. Normally, an AC cleaner will fix this but worse case, replace the air con gas. The problem is normally caused by turning off the air con. I leave it on all the time which ensures all the seals remain lubricated etc and the system remains effective.

If that is not the issue, it could be a leaking heating core in the interior of the car. Worth checking if you have ruled out the air con. Using an air con cleaner is the cheapest option so worth trying first.

[Baldilocks73]

Cabin filter dirty?