What Would Cause a Bathroom to Not Get Hot Water in the Tub Only?
By Chris Deziel Updated December 06, 2018
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When you aren't getting hot water in the bathtub and the other faucets are operating normally, you don't have to look far for the problem. It's either in the faucet or in the pipes supplying the faucet, and the latter is not common. It could be a build-up of minerals blocking the valve, but if your faucet has a single handle, it may have a scald prevention control, and the control could be misadjusted.
Adjusting the Temperature Limiter
Before you suspect mineral deposits, inspect the temperature limit adjustment on your single-handled tub faucet. To do that, remove the handle with a screwdriver or hex wrench. On most faucet models, the limiter is a plastic disk that fits on the faucet stem and prevents you from turning the faucet too far to the hot side. You can usually simply pull this disk off and rotate it a few notches to increase the temperature. You may have to rotate it clockwise or counterclockwise, depending on the faucet model.
Hard Water Blues
If your bathtub water problem developed gradually over a period of months, it could be caused by hard water, which is water with a high mineral content. These minerals tend to collect in the small openings inside faucet valves, and they restrict water flow. The hot water side of a faucet is more likely to get blocked than the cold side, because the higher temperature promotes the reactions that cause deposits to accumulate. These deposits don't have to restrict water flow directly to cause a loss of hot water. They can simply cause an obstruction that prevents you from turning the faucet all the way to the hot side.
Getting the Faucet Apart
After turning off the water to the bathtub, remove the faucet valve for a close look at its condition. First remove the handle, then either unscrew a retaining nut or pull a pin to release the valve. You should be able to slide the valve out of the housing with pliers or by reattaching the handle and pulling. If you can't, that's a good indication that mineral deposits have accumulated, but it also means you may need a valve puller to extract it.
Cleaning the Valve and Seat
If minerals have obviously clogged the valve cartridge, it may be time for a replacement, but if the valve is in otherwise good shape, you can clean the deposits by immersing the cartridge overnight in vinegar. It's a good idea to do this even if you can't see any minerals, because they could be inside the cartridge. It's also important to clean the valve seat, which you can usually remove with a seat wrench. Clean off obvious deposits with a screwdriver, and soak the seat overnight in vinegar to remove the deposits you can't scrape off.
Delta: Water Temperature
The Family Handyman: How to Repair a Leaking Tub Faucet
Polk County, Florida: Water Quality
Department of Chemistry, Washington University: Water Hardness -- Inorganic Reactions Experiment
Chris Deziel has a bachelor's degree in physics and a master's degree in humanities. Besides having an abiding interest in popular science, Deziel has been active in the building and home design trades since 1975. As a landscape builder, he helped establish two gardening companies.
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1 How to clean a showerhead, according to an expert
2 How to Repair a Lever-Type Mixing Faucet
3 How to Repair a Wall-Mounted Single-Lever Shower Faucet
4 The Hot Water Is Not Working With the Moen Single Handle Shower Faucet