In the installation manual here https://www.dometic.com/39a242ab-622...76f8ec05.fodoc
they recommend contacting the factory for most trouble shooting. You can explain the problem and they will recommend a solution.
For their warranty work their referred option: Have a Dometic authorized Servicing Dealer, perform the work needed. The customer needs to call
Dometic Customer Service Department for a recommendation as to the closest dealer. If the customer already knows
an authorized servicing dealer, the dealer should be contacted directly.
I would still contact the person who has previously looked at your refer unit and ask what he did to get it to work. The more information you are able to provide Alder Barbour and there technician the better. I would be reluctant to use him though because I find it strange that someone can say they don't know what's causing a problem but here's the solution.