Not having hot water in a bathtub can be frustrating, especially when other plumbing in the bathroom is working just fine. A number of problems can cause a tub to lack hot water when the nearby sink does not, some of which require the skill of a plumber to repair and others you can do yourself. Before calling a plumber, investigate the possible problems that may be causing your tub to produce only cold water.
A defective bathtub faucet may be the cause of the problem, particularly if you turn the faucet handle to open the faucet and no water comes out. This probably means that something is broken between the stem and the seat of the valve that controls the flow of water. You can replace a broken faucet on your own. Turn off the water supply and remove the faucet using an appropriate-size wrench. Carefully measure the hole where the faucet was installed and purchase a faucet that corresponds to this size. Replace it by following the assembly instructions.
Water Heater Malfunctioning
Bathtubs require a lot of hot water; a malfunctioning water heater may be the source of your problem. If you have an electric water heater, one or more of the heating elements may not be working properly, causing water to flow cool or lukewarm. The heater's thermostat may need to be replaced. Another common problem in both electric and gas heaters occurs when the dip tube has broken off inside the tank, allowing hot and cold water to mix. Hire a serviceman to take a look at the heater if you suspect this to be the problem.
Another possible reason why your tub is not getting sufficient hot water is a clogged pipe. Old pipes sometimes get clogged with mineral deposits due to chemical imbalances in the water. This can block hot water from reaching the bathtub faucet, even though the sink's hot water faucet is working fine. Such may be the case if you replace the faucet and still have no hot water. Hire a plumber to flush the pipes and return them to a normal functional state.
A major leak in a hot water pipe can cause the hot water faucet to flow poorly or not at all. If you notice water damage and stains on the ceiling or crawl space below the tub, you have a leak. Leaks are harder to identify when the tub is on the first floor of a slab-foundation home or apartment. Have a plumber take a look at the system if you suspect this to be the cause of the problem.