Made by Davey for Spa Quip & Spa Power
Manufacturers Code: Q80063T
If you have a Roto spa or a Monarch spa you will probably have a Spa power / Spa-quip heater fitted, they are made of plastic approximately 14" long and consist of a heater tube, water sensors and a thermal overheat sensor.
The way to test this heater is to check if it is getting power via the 2 spade connections on either end, if it is not getting power the control system or something else will be stopping your hot tub from heating.
Please note their are several types of this heater tube with different connections and different kilo watts elements attached.