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Repairing stripped threads on a cast-iron radiator

I have a cast iron radiator that will not accept a new air vent valve.  It looks as though the threads within the radiator are stripped.  How can I fix it?  Is there a bit I can buy? How do I know what size bit I need?  If there is a bit, do you know what it is called and how much they are?

The new air vent is hanging on, so I shut off the heat to the room by closing the valve all the way; is that okay?

Thank you in advance for your help, because I really need it!!


  • Charlie from wmassCharlie from wmass Member Posts: 3,925
    what is your skill level?

    also what does the radiator look like? If the area with the tapping for the air vent is beefy enough it can be drilled out and tapped for 1/4" NPT , this is for those with higher skill levels. the quicker but less visually apealling repair is as follows. Buy a 1/8" by close iron or brass pipe nipple. JB Weld epoxy, and an 1/8" coupling. Install the nipple into the coupling then apply the JB weld to the nipple and thread it into the radiator. Add a shoulder of Jb weld let the epoxy set up and harden. carefully thread the air vent into the coupling.
    Cost is what you spend , value is what you get.

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  • crash2009crash2009 Member Posts: 1,484
    I have one like that

    Its probably not what the pro's do, but it worked for me.  I just wrapped teflon tape around the threads of the vent and screwed it back in.  I had to experiment with how many layers of teflon before I got it to grab. Its been in there for 2 years now, still works.
  • acl10acl10 Posts: 193
    I used a threading bit

    I used a threading bit and it fixed my Rad. Bring the vent in and ask for the size of the threads. It may work
  • Big-AlBig-Al Member Posts: 263
    edited December 2010
    Drill, Tap, Bush

    First, I'd buy or borrow 1/8"-27 NPT tap and try to see if I could either clean up the existing threads or tap it a little deeper and get the vent to screw in better.

    If that didn't work, I'd drill it out with a 7/16" bit, tap it to 1/4"-18 NPT, and install a 1/4" to 1/8" reducing bushing.  The radiator in my kitchen is done that way . . . not because it was stripped, but because I grabbed the wrong drill bit when I tapped it the first time . . . dang bifocals! . . . .
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