Why does our unit smell like sulfur after a heavy rain?

The sulfur smell after heavy rain is usually hydrogen sulfide off the holding tank once rainwater thinned the deodorizer charge.

I have hit this on residential additions after a multi-day soak. Water sneaks in through the roof vent or a door that did not latch flush, and it dilutes the blue mix in the holding tank. Anaerobic bacteria then kick up that rotten-egg gas. It is not the water table seeping up through the gravel. Wet ground can smell earthy on its own, but the sharp sulfur punch that hits when you open the door is almost always the tank chemistry going watery.

Call for an early service visit to pump and recharge the deodorizer. Weekly service is fine in dry weather for a crew of eight, but after a hard rain you often need that extra pump so the charge is not sitting diluted for days. Until the truck comes, keep the door shut and clear any leaves or debris off the roof vent so the unit can breathe without collecting more water.