Water heaters are one of those things that are taken for granted because they are generally very reliable. Most residential water heaters in my area (Texas) use either gas or electricity to heat the water which is stored in a tank and reheated as needed.  There are also tankless water heaters available that only heat water as it is being used. While most have a warranty period of less than 10 years most last much longer than that. There are some potential problems with water heaters so here are some things to be aware of.

All water heaters have the potential of overheating water which could be disastrous. An old unit could spring a leak which while not disastrous could still cause damage. Gas-fired units that have an open flame should be kept away from combustible fumes. Dangerous problems with water heaters are rare but do happen so here are some things to be aware of.

A leak from a water heater can be a real pain depending on where in the home the unit is located. According to current building standards, if the unit is located where a leak might cause damage to the structure, it should be installed with a drain pan under it. That pan should have a drain line that discharges to the outside. Now if it develops a leak of any kind it will be diverted to the outside and not damage your home. Just be aware of where the drain line ends and pay attention to it as you work around your home. If it is leaking, you have a problem that should not be ignored.

A malfunctioning control unit or thermostat might cause the unit to overheat the water which could turn into steam which would really increase the pressure on the tank and or the hot water system. For this reason, the units are all equipped with Temperature and Pressure Relief (T & PR) valves. This is one valve that is spring-loaded and is designed to open at about 212 degrees F or 150 PSI of pressure.

The T & PR valve is located at or near the top of the tanks and somewhere on the hot water side of a tankless unit. The valves should also have a drain line attached to divert water to the outside of your home. The T & PR valves are designed to re-seat after the pressure or temperature has been reduced to a safe level.

It is important that this drain not be reduced in diameter and its termination should be within a few inches of the ground and pointing down.  Also, the end of the T & PR drain should not be threaded so it can’t be capped or plugged and the T & PR drain line should never run uphill at any point. If it does, and the valve opens it will not drain fully and the water left in the drain may cause corrosion to the T & PR valve which may not work the next time it is needed.

The T & PR drain line usually terminates very close to the pan drain. Be aware of any sign of dripping water from this drain and call a licensed plumber immediately if you see anything suspicious.  A leak in this area could indicate a serious and potentially hazardous condition.

Another concern with water heaters is combustible fumes. Folks often keep gasoline and other things that give off combustible fumes in their garage and it is not fun when those fumes drift into a water heater flame.  "BOOM" is not what you want to hear from the water heater.  While this is mainly a concern for gas-fired units it is possible for a spark from an electric contact opening or closing on an electric unit to have the same effect.

The current standards require that there be no ignition point within 18" of a garage floor. Gasoline fumes are heavier than air and will usually stay under 18" unless there is a very heavy concentration. This is why you often see garage-mounted units on stands.

I could go on for pages on this subject but I’ll stop with just one more that I see often.  The flue pipe from a gas-fired water heater gets HOT and should be kept away from combustible materials. The current standards require a 1” clearance between a heater or water heater flue and any combustible material which includes Gypsum and insulation. There is an exception to this but if your flue pipe is metal, use the 1" rule.