Tube not inflating - issue with valve?
 

Hi folks: I installed a new tube in my road bike's rear tire, but I cannot inflate the new tube. It's a presta valve. I unscrew the nut at the top of the valve, but cannot seat the pump on the valve. Also, when I push on the nut, there's no telltale "psssht". So, I don't know if there's something wrong with the valve, or it's user error. Any tips would be greatly appreciated!

One possibility is that the tube was damaged while putting things together, & it won't inflate because there's a hole in it.

Does the pump have a pressure gauge? What does it read during each compression stroke? Do you hear any air moving whilst pumping?

If you haven’t been able to get any air in there, there won’t be any leak on depressing the nut.

Are you using the pump head right? Maybe you’re trying to connect it with the head in the ”closed” position. Try again with the lever on the pump head the other way.

This may sound gross but: with the nut fully loosened on the presta valve, you should be able to blow air into the tire with your mouth. If that works, not the valve.

The other posts asked the right questions, one addtional one: the pump you are using can do presta valves, yes? And you have the inflation head (what you are pushing on the valve) in the presta setting if it can do both presta and schrader and isn't a dual use head?

Is the valve long enough that it sticks out of the rim far enough? Valves come in different lengths and if it is too short the pump won't grab it. If this isn't the issue, take the tube out and try inflating it and see what happens.

Before I bother putting tube inside tyre, I usually inflate it first... and leave overnight or longer.
Then deflate & install.

saves a lot of rework in long run ;)

In addition to what others have said, think about how a presta valve functions. There is no spring (like a shrader) to bring the valve back up to seal. It relies on the pressure in the tube. So when the tube is completely deflated, there is no pressure pushing the core back up to sealed position. You may need to try inflating a little by mouth, or maybe have the valve at 12:00 position, so the core falls closed after a pump stroke.

Make sure the valve core is tight in the stem. I just had this happen on a wheel, the valve core got slightly loose, and it would not hold air.
But wait, I just noticed OP says he can't seat the pump on the stem, that indicates he might be using the Schrader setting on the pump, as noted above.

Thanks to all for your replies. The pump seems to be fine - works fine on the front tire.

I think it is the tube - I removed the tube, inflated it a bit, and it deflated pretty quickly. Did a quick check and didn't see a hole. I should note it is an unused tube, but it had been sitting in my saddle bag for about eight years, so maybe it just exceeded its shelf life?

In any event, I'll head to the LBS and get a couple new tubes and try again. Thanks again!

Try putting the partially inflated tube in a bucket of water and you should see bubbles of air coming out from the offending leak.

Thanks again - I did find a hole in the tube. Got a couple new ones today and hopefully riding by this weekend!