Ooh, a thread for tubeless dummies: I think this is the place for me ...
(n.b. these are 33mm tyres fitted by the wheel builders, and have worked fine for ~3 years, but very few miles, and one(1) sealant top-up).
Flat tyre during practice at Xmas Cross. Pumped to 20ish psi, went down again after 1 lap. Pumped to 35ish, and despite clear hissing from somewhere, finished the race with plenty of air in.Huzzah! Still full a day later, but ...
The valve seems blocked. Unscrewed the core fully out, and ... air stayed in tyre. I'm in uncharted territory now, the bike may as well have levitated.
What now?