UKC

I have a new Stanley Flask.

When I fill it near full with boiling water, every time the lid pops open ? Why is this happening ? and is it poss to stop it ?

The bung/stopper, or the cup/lid on top?

This is a phenomenon referred to in some science text books as 'over filling'

I think the research team at Nollidge College have worked out a solution known tentatively as 'putting less in'

I have this problem with my lifeventure mug.

Hot water heats up air, that raises air pressure and lid pops.

Put a bit of hot water in, put lid on & shake it to heat up the air and the inner surfaces.

Pour out the hot water, watch out for pressure build up spitting out hot water. Fill as normal.

The hot inner surfaces warm the air so you are not sealing in cold air that then heats up so pressure increase reduced.

Although the research team at Nollidge College may have better solution.

The screw top bung is what pops off. On top of that theirs a screw cup, but it the bung below that pops off.

As has been said, I will put even less in, and hopefully that be it. but must say on my other flask the same about hot water causes no probs. 

Always put in some boiling water and lid on and shake first. I pour this out, then fill as norm, but this lid popping still went on.

Ill put even less in and hopefully that does it 

Buy a thermos with a pop up lid, when overfilled the pressure holds the valve closed and you can't open it (not without unscrewing it).

The bung is meant to be held in by the screw thread, but this fails entirely when filled? Popping out like a champagne cork, not untwisting itself?

It's likely the warming, expanding air providing the motive force as others have said. I'd still expect the threads to hold.  Sounds like it could be something along the lines of the backing structures not having enough stiffness (possibly worsened with heat...but its a flask so thats a crap excuse), or just crap design/manufacturing on the threads with too much space between/not enough engagement on the mating faces.

I would be seeking a refund and replacement with a different product.

I think you may have saved me the time of posting my "why does my bath flood the bathroom when I get in" thread

Have you tried filling as normal , but leaving the top slightly loose to let everything stablise for ten seconds or so, then tightening the lid fully ?

Your 'Eureka!' moment?

Faulty. I've had it, got it replaced, no problem with replacement.

Isn't that Greek for “That's too ****ing hot!”?

That is what Im thinking. I thought I would ask first before it goes back. My last check will be fill and leave loose for couple min then tighten, if ok well and good, but not holding my breath. I'm sure it a fault, as it never happened in any flask previously