I ahve done a search and I'll admit this topic is often asked about, but I haven't found an answer, so yes, I am starting yet another thread about Oyster cards.

I will have a zone one to four one week travel card loaded on an oyster card. I will be staying in zone four. I would like to take the tube from/to Heathrow, can I top up my oyster card or for travel from/to Heathrow or do I need to buy a separate ticket? I plan on cashing my card in at Heathrow before I leave as I am uncertain when I'll return to London, I will travel to LHR on the last day the one week pass is valid. Any suggestions will be appreciated. Thank you.

You can have PAYG cash and a Travelcard on the same card. No need to buy a separate ticket

Just tell the ticket clerk at Heathrow your situation: they'll sort out what you need.

Load PAYG (Pay as you GO) to the same Oyster card which contains your monthly/weekly travel card for that extra trip between zone 4 and LHR.

Any unused PAYG and card deposit (they used to return the deposit - not sure if the rules have changed lately) will be returned when you cash in your card at the ticket counter.

Please be aware that Travelcards (weekly/monthly) are a more complex affair in terms of refunds - and you probably cannot seek a refund (ticket counter staff will be able to tell you if you can) but then since you will be travelling to LHR on the last day of the pass that shouldn't be a problem

No problem at all - when you load up your card just tell the ticket agent what you plan to do and they will tell you what about to put on to cover the extension out to Heathrow.

What you need is an ext ension fare to cover your travel on those two days from the end of zone 4 into zone 6 so in effect the fare is the fare for a pay as you ticet for zone 5 to 6. According to the tfl web site, that fare is £1.40 peak and £1.30 off peak so since you're going to be trading in the card at the end, the clerk will put £2.80 on the card for extensions and you just touch in and touch out and the great tfl computer in the sky or wherever it is will do the math. The card now requires a deposit of £5 even if your first purchase is a 7 day travelcard (they used to waive that if your first purchase was a 7 day travelcard. I used to get a new card each time and have 5 of them now but they decided there were too many peope like me who did not just refill them and began requiring the deposit, bummer) so if you travel back to LHR off peak. you'll be refunded the 20p difference and the £5 deposit; although the ticket windows at LHR usually have moderately long queues.

A good tip: don't mix form of payment on the Oyster card. Use cash all the time, or credit card all the time. I used cash always, and the ticket agent gave me my refund in cash. Had I mixed payment type, the agent said I'd have to fill something out and wait for the refund to post to my charge card.

I piad for my oyster card with credit cad but they returned cash at London Victoria.