Heater Drain Plug alternative?

[dmcody]

Opened my pool this weekend, and while screwing in the drain plugs to the 1987 heat exchanger, I noticed that the threads for the ¾” plug were non-existent. I’m talking absolutely smooth – see photo. Don’t know what happened (other than they rusted away), but I’m looking for suggestions on plugging this hole. My first attempt will be a mechanical plug, but I’m not sure how it will fare with the elevated temperatures. Alternately I could try and rethread the hole for a larger plug. I don’t have the tap, but I’m guessing a 1” would be the next common size up. Would there be any concerns with a 1” tap?

Thanks

 

[Bama Rambler]

That's on the water side so it doesn't really get all that hot. I'd ream the hole and try and expandable plug in it. And you're right, by the way, a 1" npt would be the next size up.

 

[dmcody]

Thanks

 

[racket]

Thanks

What kind of heater has a 3/4" drain plug in the header? I know many Laars/Raypak have a 3/4" for the pressure relief.

 

[dmcody]

One that doesn't have a PRV installed. From looking at the parts breakdown, this plug is for a PRV. - Item #7. Its been like this since it was installed in 1987.