Small pieces of plastic on shower heads can indicate a degraded dip tube.
A dip tube is the cold water inlet tube into a water heater. A dip tube is specifically designed to be long enough to introduce cold water into a water heater near the bottom of the container and close to the heat source. Tube length is critical to maintaining the correct convection cycle within the heater. If the tube shortens due to the break, the heater may no longer produce an acceptable amount of hot water or may only provide lukewarm water. These tubes are also made exclusively from non-metallic materials, such as heat-resistant plastics, so they will not interfere with or damage the heater’s sacrificial anode.
Water heaters rely on the principles of convection to efficiently produce an acceptable outlet water temperature and volume. An efficient convection cycle in a water heater causes incoming cold water to concentrate around the heat source at the bottom of the tank. As the water heats up, it moves to the top of the tank, where it comes out the hot water outlet when one of the hot water faucets is turned on. The heater thermostat is usually located at the bottom of the tank in the coldest water area and as the water heats towards the bottom of the tank it reduces the heat or cuts off the heating elements altogether.
This positional relationship between cold and hot water is essential to the efficient operation of the heater and depends on the cold water being introduced to the bottom of the tank. If, for example, cold water were introduced near the top of the tank, the convection cycle would be overridden. This would have several negative effects, the most immediate being lukewarm water or a brief flow of hot water from the taps. Heating bills would also go up because the incoming cold water would simply destroy the entire operation of the heater, causing it to have to run longer to keep the water hot.
All of these factors mean that the correct length dip tube is essential to an efficient water heater system. Any sign of the above symptoms could indicate a damaged or broken dip tube. Small pieces of plastic in appliance filters, faucet aerators, and shower heads can also indicate a degraded dip tube. Fortunately, replacing a dip tube isn’t a huge expense and is, for the most part, a fairly straightforward exercise for the DIY brigade. Many dip tube variants have a flared top end, meaning you can simply fit a new tube into the heater fitting and engage the inlet spout.
Dip tubes are made of heat resistant plastic to prevent damage to the heater’s sacrificial anode and should always be replaced with tubes of similar construction. The sacrificial anode is a metal rod inserted into the tank that serves as a preferential target for corrosion, thus preventing the tank from excessive rusting. The use of metal, particularly copper, in the dip tube can damage the anode or render it ineffective, leading to eventual rust-related leaks in the tank.