I need some advice on a geyser please.
My mom's house has a 5year old kwikot 150L geyer, which we thought packed up last week. There was no water coming through any of the host water taps.
So I went there and decided to open up the geyser to see what's wrong. It's a horizontal one with the cold inlet at the bottom and warm outlet at the top. I opened the "bleeder" (is that what it's called) valve to let out the water and at first it ran very slowly. With all the hot water taps open. The inlet was shut-off. Just to see if we got enough water coming in, I opened the inlet's feed and there was a strong flow of water. So the problem should either be inside the geyser or the pipes. After some time of flushing, the water suddenly came out much faster, like it was getting air through from the taps in the house. After completely flushing the geyser I took off the big round plate where the heater element and thermostat is on and there's no build-up inside, as I expected it to be. The element and geyser walls look pretty much brand new. I couldn't see as far as the hot water outlet due to the angle of the geyser and the limit space in the roof.
But now my mom tells me the hot water is running slower and slower again. There's a copper pipe (looks like 16mm) connected to the hot water outlet, and then into the house's old galvanized pipe, attached to a T-piece Most of the pipes in the roof look fine, but there's something wrong.
My mom did mention that there's some small black stones coming from the hot water pipes, but it's been doing that for quite some time now. And they're tiny, about the size of sugar.
Is it possible to flush the system with something? Or what else can I do?