Take the Piccadilly line from central London straight to Heathrow; it’s affordable, frequent, and stops at all terminals

https://www.scribd.com/document/1074904087/Private-Hire-and-Ride-Hailing-to-Heathrow-What-to-Know-Before-You-Book-216958

Take the Piccadilly line from central London straight to Heathrow; it’s affordable, frequent, and stops at all terminals, though it can be crowded during peak travel times.