Hot tub froze, stopped using it for 2 years. Help me revive it?

[Testakount]

Hey so I have this Gulf Coast LX 11000 hot tub in my backyard that is currently out of order.

2 years ago it started acting up with an error code "rhnh" and it would occasionally just go cold on me.  Well when this would happen I would just reset it and then it would be like a week before it happened again.  Eventually it just stopped heating up reliably so I just forgot about it.  Halfway through winter I realized that the hot tub is frozen up.  I drained it and just left it sit again and now here I am 2 years later trying to get it back to life.

The controls work, all the pumps seem to work, but I think the heater is broken.  The control panel at any given moment  either shows "rhnh" which means "no heat"  or "rhHL" which means rhHL.  Before it froze it never would show rhHL.

In addition, I was looking around the inside and I noticed that the pipers were covered in grime or mold and the bottom of the tub was pretty soaked.  I think the water was because it rained pretty hard last night though, since there isn't even any water in the hot tub at the moment.

I'm thinking the heater needs to be replaced, but where should I start checking for ice damage?  I mean the electronics are still functioning and stuff, but could the

Obviously I think I need to replace the heater, but what else should I do here?  How should I asses any other damages?

Thanks

[Racenut]

Before spending money on a heater, I'd fill it and try to run to see if the ice cracked pipes, also to see if everything else still works.

[Vinny]

I agree - fill it up to a normal water height, let it sit for 24 hours and see if it holds all the water. If it does then I would start to repair it, if not look for the leaks.