It appears as an Indonesian citizen traveling through Heathrow air-side to another country you do not have to pass through border check/immigration and hence do not require a transit visa.
I need to change terminals at Heathrow. Can I transit airside?
Heathrow’s terminals are connected by dedicated buses that transport
passengers from one terminal to another airside. If your baggage has
been checked through to your final destination, you will not have to
pass UK immigration control; the buses are part of the airport’s
internal airside transit system.
You always pass through border control if you:
- leave the main airport building for any reason
- need to collect your bags and check them in to your onward flight
You must also pass through border control if both:
- your onward flight leaves on a different calendar day to when you arrive
- there’s nowhere for you to stay overnight in the airport, for example in a transit hotel