faucet leaks when shower is on: 3 causes and how to fix4 min read

Did you ever notice that when you turn on your shower, your tub faucet starts to drip? While this issue may not seem like the end of the world, you should address it before it gets worse. Here’s why your faucet leaks when the shower is on.

Your faucet may leak when the shower is on due to mineral buildup in the mechanism of the faucet, or a corroded shower diverter valve. You can replace the parts or disassemble and clean them pretty easily to attempt to stop the leaking.

Figuring out why your faucet leaks when you turn on the shower is only half the battle, of course. To get your shower back to its normal water pressure, you need to know how to repair the issue. Here I go into detail on how to fix your leaky faucet and have included pictures of my own faucet/shower system, and tutorial videos, in order to help you fix the problem.

3 most common causes of a leaky faucet whilst the shower is on

A faucet may begin to leak when the water is on elsewhere due to the following reasons:

1. Mineral Buildup

Mineral buildup is usually caused by high mineral content (calcium and magnesium) in the water. Gradually, these dissolved minerals accumulate in your pipes and fixtures, restricting the water flow. The prevalence of mineral build-up will depend on whether your water is ‘hard’ or ‘soft’ – luckily the water where I live is soft and so we rarely get mineral build-up issues.

As the water flows through the valve at a certain rate and gets blocked by the mineral buildup, it tends to find a different route — and that route may be out of a nearby faucet. This results in your tub faucet leaking when the shower is on, and, oftentimes, lower water pressure at the shower head itself.

2. Valve Issues

Another possible cause of a leaking faucet when the shower is on is a faulty shower diverter valve. 

Faucets Diverter Valve
My shower diverter valve is a simple ‘up and down’ motion. In order to remove it I screw the valve anti-clockwise.

The shower diverter valve is a device that controls water flow from the supply lines to the shower head and other components of the shower. It allows you to switch between the shower head and other parts, such as a hand-held shower head, the tub spout, or body sprayers.

Typically, the diverter valve is located in the wall near the shower head.

When the shower diverter valve is open, the water is allowed to pass through the faucet. Closing the valve, on the other hand, should redirect the water into the shower head.

If the diverter valve is faulty, not all the water will be diverted to the shower head, leading to the faucet leaking when the shower is running.

Although shower diverters are relatively simple devices, they can still experience breakdowns. There are three primary causes of shower diverter problems: a broken seal due to wear and tear, corrosion or cracking of the internal threads, and corrosion or damage to the outer finish or caulk.

3. Spout Corrosion

Spout corrosion occurs when water containing metal ions, such as iron and copper, is exposed to the air.

The metal ions react with the oxygen in the air to form a layer of rust, causing the faucet’s internal parts to corrode and loosen over time. Eventually, the faucet starts leaking when the shower is turned on. 

Corrosion of the internal parts can also lead to a restriction of water flow, which can cause the faucet to leak even when the shower is off. Spout corrosion is prevalent in older homes and is one of the most common causes of faucet leaks when the shower is on.

step-by-step fixes for a Leaky Tub Faucet

You can do the following to prevent and stop a faucet leak when the shower is on:

Remove Mineral Buildup

While several products are designed to combat mineral buildup in your bathroom and kitchen fixtures, some are pretty harsh and could damage your plumbing. Choose carefully when it comes to addressing a buildup in your pipes.

Vinegar is a great solution for mineral buildup because of its acidity. It gently breaks down the minerals, opening a clear pathway for the water to flow freely through the fixtures.

Here’s how to use vinegar to get rid of the mineral buildup:

  1. If your shower head is removable, unscrew it from its base and put it in a plastic bag. If not, wrap the plastic bag around your shower head and secure it with a rubber band.
  2. Add a generous amount of white vinegar (on Amazon) — enough to submerge the shower head.
  3. Seal the plastic bag and let the showerhead soak for several hours or overnight.
  4. Take out the showerhead, dry it and reattach it.
  5. Turn on the shower and test whether your faucet still leaks.

I found this useful video on how to replace your showerhead:

If mineral buildup was the culprit, you should now have steady water pressure when showering.

Replace Any Defective Parts 

A faucet leak when the shower is on sometimes means that one or more parts that make up the faucet assembly are defective or worn out. This could be due to regular wear and tear, poor installation, or a faulty component. The defective parts may include the spout, spigot, or diverter valve. 

You can replace the defective parts by following these steps:

  1. Turn off the water supply to the faucet. 
  2. Unscrew the spout, spigot, and diverter valve from the faucet. 
  3. Take the old parts to the hardware store and purchase new replacement parts. The simplest and best way to get the right parts for your dripping faucet is to take the old ones to a hardware store and ask for identical replacements. 
  4. Install the new parts according to the manufacturer’s instructions. 
  5. Connect everything back into place, making sure you tighten all connections securely.
  6. Turn the water supply back on, and test the shower to see if you’ve resolved the issue. 

If the leak persists, you may need to check for other possible causes, such as issues with the O-rings.

This can happen when the O-ring seals around the spout, spigot, or diverter valve become worn or damaged, resulting in a leak. In some cases, the O-ring can become clogged with sediment or debris, leading to a leak. 

The solution is to replace the O-ring seals around the spout, spigot, or diverter valve. If the O-ring is clogged, clean it with a brush or other appropriate tool before replacing it.

It’s also important to ensure that the O-ring is properly seated in the groove of the spout, spigot, or diverter valve before tightening it with a wrench.

If you have no plumbing experience, then it may be a good idea to hire a licensed professional to fix your leaky faucet.

I found this useful video which takes you from start to finish on how to replace the tub spout diverter:

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Hi, I'm Ed, and I run BuildFanatic! I enjoy providing the best possible information on a range of home improvement topics.

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