1998 Prowler Water Pump/Water Heater

I have a problem with my water pump and it's probably the strangest thing I've ever seen on an RV. It has a standard water pump mounted on the couch and a Atwood gas/electric water heater. When you turn the switch on for the gas part of the water heater it works fine. When you turn the water pump switch on it does nothing except turn just the gas on for the water heater- no ignitor. I removed all terminals on the water heater and for the time being the water pump is working normally without opening the gas solenoid. What can possibly be causing the water pump switch to turn on the gas solenoid???