Bough a pool home 6 months ago, tried starting LAARS LX400 heater for the 1st time today and have gotten Service High Limit error code. The heater has not been started for at least a few years and looks like it needs cleaning and TLC. I have downloaded service and operation manuals, and I am trying to open the front panel (door). It has two knobs. I have tried turning the knobs, moving the knobs up / down / left / right with not much motion in the knobs. I do not want to break anything and the front door does not want to come off. Any advice to removing the front panel? Do I turn the knobs to shift them? It is possible for locking mechanism to be rusted?
What service may this heater need? I have read this is not the most reliable heater, but I wan to give it a try reviving it.