I had air check valve above the circuit board/heater/pump etc. leaking water on my 1999 Tiger river Siberian tub. I replaced the valve and dried out everything. When I switch the breakers on the 20 amp stays on powering the pump, etc. but the 30 amp immediately trips. I checked the red switch on the heater but it is not tripped. The red diode on the circuit board is on showing power to the heater. If I unplug the 2 wires from the circuit board to the heater limit switches the 30amp breaker stays on, as soon as I plug these back in the breaker trips. I had no problems before the water leak. It is a no fault 6000 heater.

The heater is leaking current to ground. It's a sealed unit, if water got inside the assymbly, it may not ever dry out.
Heater replacement will solve your problem, but you *might* be able to repair your original heater simply by giving it ample time to dry... or, if you're feeling up to it, dis-assemble the heater and dry let it dry. Just the box on the end that contains the high-limit needs to be dissasembled. Don't remove the end caps.
If you happen to ruin the heater, no worries, a new one would have been neccesary anyway.

On a side note, if you need heater replacement, the No-Fault 6000 has been replaced with a PDR No-Fault, no more annoying high-limit that needs to be re-set manually. It's a better heater.

Good luck,

~Swine

Do I need to drain the water before disassembling heater?