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That would usually indicate that the heating element for the 240 VAC mode is burned out. That can be checked pretty easily with an ohm meter. If you have one I can direct you in this or any shop can do this for you in just a few minutes. At the same time they can check (or you can) to be sure that a fuse on the circuit isn't blown or perhaps a problem at the service breaker that controls that circuit. There are other things that might cause this, but those are the most common and should be checked first. Hope that helps here. Please get back to me if you need more on this after you check those things and we can dig deeper here. Thanks!
Were you able to check this out yet? I am adding a link to the Dometic Service Manual which covers this. It is the same as our RM2453 model. Print out a copy so you have it or Bookmark it so you can come back to it again later. Let me know if you need more on this. Thanks! http://bryantrv.com/docs2/docs/rm2510_52.pdf