The reason for the E90 error message on the hot tub may be due to a damaged filter pump. The heating of the spa hot tub depends on the correct functioning of the circulation pump. So first check that the pump is working. If the pump is fine, the problem is likely to be in the heating element, temperature sensor or other component of the heating system. For warranty repairs, contact your dealer. If the spa is out of warranty, you can contact us using our online form.