Losing water pressure can be caused by a variety of reasons, but only losing hot water pressure eliminates a majority of those problems. Hot water pressure begins at the hot water heater in the home. The water flows through the pipes that carry the hot water to the showers and faucets. Low pressure in the hot water line is created by only a few problems.
Electrical or Gas
A residential hot water heater is operated or powered by electricity or gas. A problem with the electrical system or gas power will cause low hot water pressure. Check the power supply at the main panel first on an electric hot water heater and the gas shutoff switch on a gas-powered hot water heater. The power supply does build up pressure inside the tank when heating the cold water. Once the water is not heated by the power supply the water pressure can go down.
Cold Water Line
The pressure coming from the cold water line is the same pressure that comes out of the hot water heater. A problem with the cold water line pressure will cause low hot water pressure. The hot water heater will not fill up as quickly and push hot water back out of the tank if the cold water line running into the tank is too low. The problem generally arises when there is a problem with the city water system or water tank supplying all the water to the home. Check with the local water company if this is the problem.
Hot water heaters build up sediment over time. Rust or debris gets into the hot water lines causing low water pressure to develop. Ben Franklin Plumbing in Denver, Colorado, recommends draining and flushing the hot water heater every three months as part of a regular maintenance schedule. Flushing the hot water tank and lines prevents sediment from building up in the hot water lines which can cause low hot water pressure.
The hot water heater is not always the cause of low hot water pressure. Low hot water pressure can be localised, such as at one shower head or one sink faucet. If only one water outlet has low hot water pressure, the problem is either with that hot water line or the faucet itself. A shower head can be removed and cleaned to fix this low-pressure problem. The faucet needs the mouth pieces or spigot removed and cleaned to repair this problem. If cleaning the water outlets does not fix the low hot water pressure at the localised area, the problem is in just that one water line that leads to the one shower or sink, such as a clogged pipe running into that one shower or sink.
Under the sinks and at the hot water heater, a water shutoff valve is required. The shutoff valves turn the water off at one location instead of the entire home. The shutoff valves do break or clog over time. The only way to determine if this is causing the low hot water pressure is to remove the shutoff valve and replace the part. Since the shutoff valve is attached to the hot water line, the part must be cut off and replaced with a new shutoff valve. It is recommended that this low hot water pressure problem be performed by a qualified plumber.