Originally Posted by blagger

The United site can be helpful, but it's flaky itself, and finding what you want is a bit of an art. I just now randomly picked 15 March on the United site and it showed nonstop DUB-SEA seats available in J. I then went to Avios and (eventually) confirmed 4Y, 3J seats are available on that date. If it helps, the UA taxes for EI on that flight are 37.98, so if you do a (one way, business, nonstop, flexible dates) search and you see taxes higher than that for a day then you know there are definitely no EI seats available. For the other dates you need to click each day (which is slow, but much faster than searching on Avios). I quickly clicked a few more and quickly found availability on March 5, and then searched on Avios and it shows 4J available

ETA: The United flexible dates search shows prices (hits) for a day even when you search for nonstop but there's no nonstop available that day. That's why you need to click individual dates to see if there's actually a nonstop (EI) flight available