Water Heater Mini Explosion

I have a Cobra 24-foot motorhome with a water heater problem. When I turn on the ignitor it explodes when igniting the propane, when it finally does. A loud boom! I can hear the ignitor clicking before it does light. Can you give me some suggestions? It seems to be the worst when it is a little cold outside.
Dan, (Tucson, AZ)

Dan, it’s my hunch your unit may have a partial blockage in the curved mixing tube. Plus, I would venture your water heater is in need of what is commonly referred to as a "clean and service."

All LP appliances require yearly preventive maintenance in order to remain at optimum operating efficiency. Performed each season, this set of specific maintenance procedures will minimize if not virtually eliminate all appliance operation failures. Too lengthy to list comprehensively in the column, some of the steps include setting the incoming LP line pressure, cleaning soot and carbon build-up from probes and sensors and checking/adjusting the appropriate gap spacing.

In addition, cleaning electrical contacts, checking circuit board functions, etc. are all items mandated by virtually all appliance manufacturers.

Specifically, I would have the LP gas pressure at the water heater checked and the adjustment of the primary air shutter. Misalignment of the burner tube could also lead to your symptoms. But I would look close for a blockage of sorts in the burner tube itself, impeding or disrupting the normal flow of incoming LP as it is mixed with the primary air.