HeaterCraft Heater

I need some help from the Heater experts here:

I have installed a 2 port heater into my boat from HeaterCraft and I'm having some problems with the electrical aspect. I've hooked up the power wires to spliced areas behind the dash that are pre-marked. My MasterCraft came off the line with a designated switch and wiring setup for the heater. The heater is working great but after using it for 2-3 minutes it trips the breaker. I can reset the breaker but this keeps reoccurring. I've double checked the power wires to make sure there is a good connection and they should not be an issue.

The only other issue would be the ground wire. I ran the ground to the negative terminal on the battery using both sides of a 18 gauge speaker wire. Could this be causing the problem? There is a negative grounding point behind the dash - would it make a difference if I used that? Do I need a bigger gauge wire for the ground? Any ideas....?

It is not the ground, although it sounds like replacing it with a larger wire to the battery would be a good thing. If the ground was the problem the wire would melt. Simply the breaker is not big enough, but that leads to a question...what size wire comes off the breaker? The circuit may not be large enough for your application. What size breaker is in there now and how much amperage do the instructions say the heater unit draws?

look for a 15 amp breaker and wire it into the positive with a piggy back wire clip, then wire the 2nd to the bus bar. Check all the connections and make sure it is not grounding out.