I too have been struck by the dreaded, undocumented error code "OtA" only after 4 weeks of service. I purchased the AquaPro 800 model (83,000BTU) from Costco online. It arrived in less than a week and the installation was easy. It heated the pool up from 68F to 84F in less than a 24hr period. I was very pleased with this purchase until I noticed the drop in temp a few days ago and the error code. I just called the problem in today... the woman I spoke with seemed aware of the code and mentioned that a "component" would need replacement to fix the problem. Now I'll just have to wait... I have to say it's rather annoying to have such a new/expensive purchase break like this... If ANYTHING else happens with this unit this season... this unit is going back to Costco and I will seek another heat pump vendor. I'll keep updating as this issue moves on to resolution.