Moen Posi Temp Catridge

I have a shower with a Moen single lever posi temp valve. It was getting hot but only for about 30 seconds before it would go completely cold. A plumber replaced the cartridge and then said there was no hot water at all ... so he reversed the cartridge 180 degrees to see if that would fix it. He then told me there was still no hot water and there must be a problem with my hot and cold water lines being crossed in a wall somewhere???

However, when I tested the water tonight there is warm water when it is in the cold position ... leading me to think the cartridge needs to be reversed back 180 degrees. Should this fix the problem? If it doesn't and there is still no hot water like he said, does anyone have any ideas on what the problem is?

I have little faith in this plumber and he is working for my home warranty company and isn't very helpful. My other question is if there is a temperature control on the cartridge or valve somewhere that could be contributing to the problem.

Thanks!