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

https://www.scribd.com/document/1074929924/National-Rail-to-Heathrow-Routes-Transfers-and-Tickets-Explained-232993

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.