I have always kept my coach plugged in, to a 15 amp outlet. Recently I had my electrical service upgraded and I now have a dedicated 30 amp outlet for the coach. I noticed that now, my house batteries are literally, boiling over. I unplugged, but am at a loss as to why this should happen. Help please!

Letting the batteries get low on water will cause that.
I doubt if the upgrade had anything to do with it.

If the water level is okay, check the converter voltage on the batteries. It should be from 13.2 to 13.8 or so.

The water levels in batteries should always be kept up to a 1/4" above the plates in the individual cells. I doubt very much that the boiling action in the cells was caused by the upgrad of your electrical service. I upgraded my electrical service in my yard from 15 amp to 30 amp, to accommodate the motorhome. First, how old are the batteries? The battery council has stated that the average life of a battery is approximately 3 1/2 years, especially deep cycle batteries. What you need to look for once the batteries are cool, is to take a hydrometer reading of each cell of each battery. A fully charged battery should have specific gravity readings anywhere from 12.60 - 12.75. If you have any specific cell that is more than 50 points different than the other cells, this usually indicates a bad cell, which means a bad battery. If the cell or cells are shorted, they will boil when a charger or load is applied to the batteries.

My charger went bad and was throwing 24 volts to the batteries, causeing the batteries to boil, replaced the charger with a new one with the charge wizard option. works great.