Your water heater needs regular maintenance just like any appliance, and that's the best way to ensure the water heater stays in good shape. But sometimes things still go wrong, leaving you with a water heater in trouble. The sooner you spot something out of the ordinary, the easier it will be to save the water heater and fix the problem before it has major consequences. These clues can be obvious or difficult to detect, but once you spot them, you need to call a plumber for help.
Rust and Rusty Water
This is one of the trickier aspects because you have to determine where the rust and rusty water came from. An old water heater tank that's rusting on the inside can produce rusty water as particles flake off the surface of the tank's interior — or there could be an issue with city water that's headed into the plumbing in your house. If it's something like city water, you'll want to call a plumber to find out how to prevent that rusty water from damaging your water heater (with luck, all you'll need to do is flush out the water heater and pipes). If the rust is actually coming from inside the tank, though, that's a sign you need to replace the tank.
Low Water Flow
Low water flow indicates a blockage or a leak, both of which are obviously bad and need attention immediately. You should look around the water heater to see if you can find anything, but the leak could be in a pipe outside the home, too. A blockage that doesn't let much hot water through to your faucets means you have little hot water, which is a habitability violation and health risk.
Particles in the Water
If you turn on the hot water tap and see particles in the water (you might not see them in the running water, but if you fill up a glass, you will), your water heater could have an excessive amount of sediment in it. The sediment can build up and block water lines, and it can create an environment inside the water heater that is conducive to rusting. Plus, you don't want to ingest any of those particles. Call a plumber as soon as you can.
Most plumbing contractors will work on water heaters, and there are plumbers who specialize in the appliances, too. Have them come out as soon as possible; these aren't things you want to push off to the next morning or next business day. Rust, excessive sediment, and low flow are signs something needs to be fixed immediately.