Is It Worth Repairing a Water Heater?

The unit is relatively young, the issue is a replaceable part (element, thermostat, anode in some cases), and there is no tank leak.

The tank is leaking, the unit is near end of life, or repair cost approaches replacement value.

If the tank is leaking onto the floor, treat it as urgent: shut off power or gas if you can do so safely, shut the cold-water supply, and call. A website cannot tell you how many years a tank has left. Details: water heater services.