Every home deep fryer I ever bought never came up to temp. Last one was a real bummer. USing a candy thermometer, one of known accuracy, when setting the Rival to 350, waiting for the green light, and then waiting an extra 10-20 minutes "to be sure", the temp never got over 220. When set to 375, and following the same routine, the temp never got over 240F.
They were very willing to replace it. However the catch was, I had to pay shipping to ship the defective unit back and shipping to get the replacement. Adding that up was more than I paid at Home Depot for the first one.
No guarantee that the next one would work any better, and Home Depot wouldn't take the first one back.
I've had Fry Daddy, Fry Baby, Waring, Rival, and a couple others before I gave up. Use a nice heavy pot on the gas range, and learn how to adjust the temperature to keep it at the desired spot, and it actually works pretty good. Just be careful when adding anything cold!