Hoping someone can help me troubleshoot this.

I have this iSUP..www.kitedanmark.dk/naked-race-addict-oppustelig-sup.html
Bought second hand, good condition. Have been paddling for about 6 months now in Copenhagen, Denmark, having fun!

However when I inflate it from 5PSI up to 15PSI the needle starts going fown, while I am inflating it. This is visible when I stop pumping...the needle starts creeping downwards. I cant hear any sound. Is the board really deflating???

This creates a panic where I have to really pump intensively and fight against the deflate to get up to the 15PSI.
Once I have removed the pump hose, and screwed the cover over the valve, all is fine. During paddling it doesnt seem to leak.

I researched a bit and then thought that the little plastic bridge inside the hose might be pressing on the valve a bit, causing it to deflate, so I cut that out with a penknife, so now it fully relies on the pressure to push the valve down and let air in.

What should I check for next...should I research getting a new valve installed? Or could it be the pump, the needle or pump hose? Suggestions welcome.

I have three inflatibles now from the same brand, so i have three identical pumps. I was pumping up my new fishing isup, with my oldest pump and i noticed this was happening to me. I had pumped it up to 5 psi and then reconnected and this sensation was happening to me. I think it was the pump, or hose, def. not the board if that helps. Just happened yesterday so ill keep you posted.

It'll be a valve in your pump. Dismantle it and have a look at the head.

Hose problem, tried other pump today and no worries, cgeck for air leakage at hose connector to pump and gauge at pump.

Thanks for the tips both, I will check the hose for leaks and perhaps try to open up the pump. I cleaned the hose a bit recently from chalk build-up, and maybe that has also helped.