Over the years, sediment scale and mineral deposits tend to build up at the base of the tank. Manufacturers suggest that a few quarts of water be periodically drained from the water heater to help remove these deposits. However, this practice is not always effective, and if sufficient deposits accumulate, a rumbling or pounding sound can be heard when the unit is firing. If you hear a rumbling noise while inspecting the water heater, do not be alarmed. It is not a dangerous condition, although the noise can be annoying. In addition to their annoyance value, accumulated deposits at the base of the tank can act as an insulator between the water and the flame, decreasing the overall efficiency of operation.
All oil- and gas-fired water heaters must have an exhaust stack to vent the products of combustion to the outside. If you find an exhaust stack that is loose or broken, so that the exhaust gases are discharging directly into the house (see FIG. 16-5), you should notify the homeowner of this potentially dangerous condition. As with a heating system, the exhaust pipe should have an upward pitch from the heater to the chimney connection. The exhaust pipe gets quite hot and therefore should not be in contact with combustible material.
The water heater should be inspected while the burner is operational. This can be achieved by opening the hot-water faucet at a nearby sink. Within a few minutes, depending on the size of the tank and the water flow at the sink, the burner should fire. (This assumes that the pilot is lit for a gas burner or that the electronic ignition is operational for an oil burner, and that there is oil in the storage tank .) If the burner fails to fire, there is a problem condition that should be checked. Oil and gas burners and their controls are discussed in detail in chapter 15.
To provide an adequate draft for combustion gases, oil-fired units should have a draft regulator, and gas-fired units should have a draft diverter. (See FIG. 16-6.) After the unit has been firing for several minutes, check the draft in a gas-fired unit. Put your hand near the draft diverter. If you feel a flow of gases on your hand, there is either a blockage in the flue passage or there is a negative pressure in the house. This is a condition that must be corrected.
Whenever there is a heavy draw of water, if the temperature of the inlet water is low, condensation can form on the tank. If this should occur, you might see some water beneath the heater; in a gas-fired unit, you may hear sizzling or pinging sounds caused by water droplets falling on the burner. Consequently, if you see a little water on the floor or hear the pinging noise of droplets, do not assume that the water heater is leaking; it may be condensation. If it is, the condition will disappear after the water in the heater becomes heated. If the condition does not disappear, a leak should be suspected, and the unit may require replacement.
If you notice a water pipe connected to the drain fitting at the bottom of the tank, it is probably a hot-water return line. This is the typical connection for providing “instant” hot water at the bathroom fixture that is farthest from the water heater. It is more often found in large pricey houses than in more modest homes. You can check out the effectiveness of the instant hot-water system during the interior inspection of the bathrooms.
As with a gas-fired heating system, the pipe supplying gas to a domestic water heater should be rigid black iron and not a copper pipe or a flexible pipe. If the pipe is not black iron, check with the utility company for its requirements.
Some gas-fired water heaters use bottled gas (propane) because natural gas is not available. In that case, a copper gas-supply pipe is usually acceptable because the supplier provides a quality control over the impurities in the gas. All impurities that would react with the copper are removed.