Hotend not reaching target temp

[GMTH]

This just started happening last week. We have a Rostock Max V2. Start the machine, set the temp, and notice the hotend is climbing much slower than usual. The heated bed reaches target temp long before the hotend gets close. Hotend climbs slowly and stalls a bit as it gets hotter. Stalls completely at ~200 degrees celcius. I ran the PID autotune but it failed twice. Anyone experience this before? Can anyone offer advice on the next steps?

C

[Xenocrates]

Check the hotend resistance. It's likely too high, as a resistor failed open.