The answer to 'heat pump smells bad' is that a foul odor coming from your heat pump is usually a sign of an underlying issue that requires attention. Common causes include mold or mildew buildup, a refrigerant leak, or a problem with the compressor or other internal components. The smell may be musty, rotten, or similar to burning rubber.
If the odor is mild, you may be able to address it yourself by cleaning the outdoor unit, changing the air filter, and ensuring proper drainage. However, if the smell is strong or persistent, it's best to call in a professional HVAC technician to diagnose and repair the issue. They can thoroughly inspect the system, identify the root cause, and make any necessary repairs or replacements to restore proper operation and eliminate the unpleasant odor.