I have an Hitachi NR90AC5. It's oiled and has adequate pressure. There's something that's gone wrong with it recently, where it sometimes double fires (in single fire mode) and then the piston gets stuck down. I cannot push the piston back up by hand with the air disconnected).

I took it to a place, and they said it just needed cleaning and they cleaned it. But after I got it back it nailed off two more boards then stopped working again- same issue with the piston getting stuck down. I have an identical gun that works fine, so it's not the "cold" weather. (It's in the 40's-50's).

This gun was purchased in April. I'm just framing my own house, so it's not used that heavily.

I've repaired my finish nailer before, but I need to know what part to replace and where on the gun you open to fix it. It's not always obvious that a "bad" part is bad when looking at it. On my finish nailer, the bad part looked just fine. But after replacing the part, the gun worked correctly.

Does anyone know what part or parts to replace on this framing nailer that causes the symptom of a hard stuck down piston (sometimes preceded by double firing)?

  • If you can't push the piston back up, how are you resetting it? Does it need to be disassembled to fix it? – JPhi1618 Nov 15 '19 at 16:52
  • Yes, it had to be dissembled to reset it. I had a shop do it. They said it just needed cleaned. But after that it shot a few clips and did it again. – Nick Nov 15 '19 at 17:20
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    If you just bought it in April, is it still under warranty? If so, just exchange it for a new one. Let the factory figure out how to fix it and sell it as a refurb. – FreeMan Nov 15 '19 at 19:43
  • Warranties don't cover seals, orings, etc. Nearest authorized repair center is hours away, and if it's a "wear and tear" part, it won't be covered anyway. – Nick Nov 15 '19 at 20:00
  • mail it to the repair centre – jsotola Nov 16 '19 at 1:49

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