After years of faithful service, the original heated bed on my R1+ might be on its way out. I get the error message "Err: TEMP FALL ERROR" on my lcd screen. When I pre-heat thru the lcd menu, the extruder temp reaches fairly quickly, but the bed temp now takes a while, about 10-15 minutes to reach temp, so I'm fairly certain the error is from the bed. Where can I purchase a replacement bed? If that's not possible. what would my next steps be?