Wynand, thanks for clarifying! Sure, IST is your final destination and I was wrong in my previous post presenting WAW in LHR – WAW - BUD (stopover) – ZRH - IST (final destination) - ZRH – LHR as final destination. Sorry for the confusion!

What I was trying to say: You do not travel in one continuous direction on your outbound leg, assuming that free tickets are based on routings (and not on mileage). You are backtracking from WAW via BUD to ZRH and forward to your final destination IST. Further more, I think that the advise you heard that transiting ZRH twice would make the IST section count as a side-trip is not correct, because the no-side-trip-rule says: The same airport may not appear more than once in either the outbound or the homebound itinerary. If the advise you heard would be correct, you could easily change ZRH with BRU (flying on TK and SN) on your homebound itinerary making LHR - WAW- BUD (stopover) – ZRH – IST (final destination) – BRU – LHR in one ticket. But in my opinion, this does not work!

I hope I do not boring you if I come up with a new suggestion with an itinerary for one free ticket assuming that you have to be in WAW for less than 24h:

LHR – ZRH – (LX 317) – BUD (LX 2250; stopover) – WAW (LO 5536 or LO 532) – IST (LO 135; final destination) - ZRH (LX 1805) – LHR (LX 454)

Besides that, LHR – ZRH (LX 317) – BUD (LX 2250; stopover) – IST (TK 1436; final destination) – ZRH (LX 1805) – LHR (LX 454) should be one ticket.

Have fun!