As you wait for your tub to be fixed, it is likely that you need to add supplemental heat to prevent the pipes under your hot tub from freezing. As you do so, you will want to check on temperatures multiple times per day, especially to start off with.
If your tub is full, don’t drain it! Unless you are also going to blow out the lines. Water, even cold water, contains a certain amount of heat, so when you drain the tub you are losing the stored heat in the water. Draining the water out of the hot tub leaves residual water in the lines which now freezes faster with the loss of the stored heat from the main body of water.
If your tub is still full and running (the water is able to circulate), a bucket heater can help to keep the water warm. A 1000 watt bucket heater, (available on Amazon and sometimes at Peavy Mart) placed in tub with the water circulating should keep the water warm. The temperature cutoff on the bucket heaters we are familiar with is 180F (too hot for your tub!) so you will need to watch the temperature regularly and unplug the heater periodically if the temperature is getting too high.
If the water in your tub is not circulating it is important to get a space heater inside the equipment area. How soon it is important to get a space heater in the equipment area depends on outside temperatures. Please note, the water in the lines is the concern, not the water in the main body of the tub. Having the water in the tub freeze solid generally doesn’t damage the shell. However, depending on your tub, the water inside the tub can still be warm and frost damage can already have occurred in the plumbing.
A 1500 watt space heater, with fan and thermostat control, would be preferable. Space heaters with less than 1500 watt capacity may not have the power needed to keep your tub adequately warm. Certain tubs may need more than one space heater. When setting the heater into the equipment area, try to avoid directing the heat at any plumbing. Set the thermostat to half as a starting point, you may need to adjust if it gets too hot or too cold) and keep the fan on high. Then seal the area as much as you can to keep the heat contained in the equipment area. Placing the outdoor sensor of an indoor/outdoor thermometer in the equipment area away from the heater can help you keep an eye on the temperature.
