Attwood water heater drain plugged

Shoot some vinegar in the hole to see if it will loosen the deposits? Just a thought.

Drill it out carefully so you don't bugger the threads.

I tried some CLR and left it for awhile but no luck.

Never heard of an anode with a wire in it. Anodes are designed to deteriorate, instead of more important metal parts. You might have a hotrod or similar installed. In any event, I'd spray it with penetrating oil then use a reverse thread drill bit and drill to drill a hole. With luck, it'll come on out, if not, get after it with an EZ Out.
Worst case, drill it out until the metal of the rod is thin enough to collapse and pick out of the threaded hole. Chase the drain threads and insert a new plug/anode.

Attwood heater using an anode rod? Pretty rare at least as most Attwood units do not require an anode so someone may have butchered the job of installing one. With an aluminum tank and a nylon plug there is no reason to have an anode.

Attwood did make a model that had an anode.. And Surburan, I'm told makes one that does not, But as noted they are rare birds.

If the plug came out completly, I'd try pushing it INTO the water heater, then CLR or Viniger and pull it out.. I do agree it sounds like a Hott Rod

Some anodes use a steel wire to support the anode material.
Atwoods with an aluminum tank do not use anodes.
You maybe able to disolve some of the material to get to drain with CLR or maybe some Lemi-shine diswasher cleaner.
Remove pressure releif valve and pour in there.
You may even be able to drill a hole in the end of anode, then use an easy out to get it out. Don't put too much pressure on drill or it will fall inside the tank.

It is an anode rod and not a hot rod. It has the steel wire in the centre like all the aftermarket ones you see for sale at RV parts stores for Attwood water heaters. I have been squirting CLR around it and pulling on the steel wire with visegrips. It is in there so tight that the water doesn't even leak out. If the wire pulls out or breaks then I may try and drill.

Thanks for all of the tips on how to repair this. I managed to drill it out, started with a small bit and driilled most of the center wire, then went bigger and bigger till there was only a small amount left. Was able to pull it out Borrowed a 1/2" NPT tap from the plumber and fixed the threads. Tank had not been cleaned for a long time, flushed about 5 lb of******out of it.

Thanks for the update!