Just in case I'm being dim. Had a slow puncture on my front wheel tonight. Nothing in rubber, but loosing air past three nipples on different sides of wheel. ages since i built these. Must be leaking past the valve and through channel between two wall skins? Why only 3 nipples on different sides of wheel?

Yes, air is getting past the base of the valve. Try cleaning up the existing valve and tightening it up – otherwise a new valve will sort it.

No idea why it's only coming out 3 nipples though, when I've had this it's come out all the nips.

Must be leaking past the valve and through channel between two wall skins?

Seems right.

Why only 3 nipples on different sides of wheel?

**** knows, sot the valve out and forget about it.

cheers guys. thought I wasn't going mad. get that sorted this evening then.

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Why only 3 nipples on different sides of wheel?

Some sealant's leaked through and sealed most of the nipples up? Matters not, but it's a suggestion! 🙂