How to unclog tankless water heater?

Question

Hi, we just survived hurricane Eta. When we reconnected all the PVC pipes the mudslides took away, we made sure the water would come out of the faucets clean before running the hot water. Still, we see a decrease in pressure in the hot water. I see on Youtube some very complicated heaters being purged. They have all kinds of valves. Here in Costa Rica they are much simpler: water in, water out. Do I really need to have the heater serviced, or can I just run some water in reverse into the heater with a garden hose? NOTE: I'm not talking about scale, but bits of rock. Thanks.

Answer 1

there is a water filter on the inlet of the heater so remove it clean then put it back , problem solved 

Answer 2

flush in reverse is worth trying, don't you think?  and i'd want a screen on that hose