Why Does Tub Faucet Leak when the Shower is on?
When you have a bathtub-shower combo in your house, you must have a shower diverter knob on the tub spout or a separate shower diverter valve to divert water from the tub spout to the shower head if you want to take a shower.
If your bathtub faucet spout is leaking when the shower is on, it means that the shower diverter valve is no longer sealing due to a worn out washer or minerals deposits. While repairs are possible, the best thing would be to replace the bathtub spout or the shower diverter valve.
Different houses have different valve installations. You will either have a:
- Single handle shower faucet
- Double handle shower faucet
- Three handle shower faucet
With a single handle shower faucet, the handle is used to adjust both the temperature and pressure of the water flowing to the shower head and tub spout. The tub spout will have a diverter knob at the top.
A double shower faucet has 2 handles, one for the hot water and the other for the cold water. Its tub spout will also have a shower diverter knob at the top.
If you have a three handle shower faucet, the left and the right handles will turn the cold and hot water on or off, while the middle handle controls the shower diverter valve. With these faucets, the bathtub spout has no diverter knob at the top.
If you have a three handle bathtub faucet which is leaking, the shower diverter’s valve seat washer is worn out and no longer sealing. You can decide to only replace the washer but if the valve has been in place for a long time you should replace the whole valve.
A single or double handle bathtub faucet that is leaking when the shower is on is caused by a worn out or stuck shower diverter. You can try to clean the diverter groove buy if that fails go ahead and replace the tub spout.
Now let us look at how to fix a bathtub faucet that leaks when the shower is on, starting with a single or double shower bathtub handle faucet.
How to Fix a Shower Diverter that Leaks when the Shower is on
If you have a single or double handle shower/bathtub faucet, you will see a small knob at the top of the tub spout. This is the knob that you pull up to send water to the shower head or push down to have water flowing through the spout.
The knob is connected to a piece of nylon inside the spout which works like a gate. There is a groove inside the spout where the piece of nylon moves up and down.
When the knob is pulled up, the piece of nylon blocks off the spout’s opening so that the water can flow to the shower head. Pushing the known down opens the spout and water flows out through the spout thanks to gravity.
Sometimes minerals deposits or corrosions can inhibit the full length up and down movement of the diverter, preventing it from making a good seal. When that happens, water will leaks from the tub spout when you turn on the shower.
Another thing that can happen is that the piece of nylon can also break off, again preventing the diverter from making a proper seal.
With a broken shower diverter, you will need to replace the tub spout. If the groove is just dirty or corroded, cleaning it might be enough to fix the problem.
Bathtub spouts also have a washer which if worn out will also cause the tub spout to leak when you turn on the shower. In this case you will also need to replace the spout.
Let us now look at the different ways to fix a shower diverter that is leaking.
1. Soak the Diverter in Vinegar
Vinegar is very effective in removing mineral buildup in faucets. It is a mild acid which dissolves the calcium and in this case allowing the shower diverter to move freely and make a proper seal.
- Fill a plastic bag with white vinegar up to the ½ full level.
- Insert the tub spout in the vinegar and secure the bag with a rubber band at the back of the spout.
- Let the vinegar do its magic for a few hours or preferably overnight.
- Remove the vinegar and pull the diverter knob up and down a couple of times
- Pull it up one more time and turn on the faucet so that water flows to the shower head.
- Check if the tub spout is still leaking.
If the leak stops, your problem is fixed while if it doesn’t, you will need to do more.
2. File the Shower Diverter Groove
A quick method to fix a sticky and leaking shower diverter is to file the groove inside the spout. It will however require you to have a small file.
This is how to do it:
- Pull the shower diverter knob all the way up. This lifts the nylon piece off the groove allowing you to work on it.
- Use the file to scrape off mineral deposits and corrosion from the groove.
- Push and pull the knob a couple of times to make sure you have removed as much dirt as possible.
Check if this solves your problem.
If while trying to clean the shower diverter grove you notice that the piece of nylon is broken, a replacement is the only solution. Lucky for you, replacing a shower spout is quite easy.
3. Replace the Bathtub Spout
There are 2 types of bathtub spouts with a shower diverter. You will either have a slip-on tub spout or a threaded spout.
Slip-on bathtub spout are simple slid in the water supply pipe and fastened using an Allen screw. Threaded bathtub spouts as their name suggests are usually threaded on the water supply pipe.
So, how do you know what type of tub spout you have? Just run a finger under the base of the spout. If you feel a hole, that is the Allen screw hole and you therefore have a slip-on spout. When there is no hole you have a threaded spout.
Before replacing a bathtub spout, make sure you buy a similar one to the one you already have. If possible, buy an original replacement from the manufacturer.
How to Replace a Slip-on Bathtub Spout
- Start by plugging off the bathtub spout so as not to lose anything down the drain.
- If the spout is caulked to the wall cut through the caulk with a putty knife.
- Use an Allen wrench to remove the Allen screw from underneath the spout.
- Put the screw in a safe place just in case you might want to reuse it.
- Hold the spout with both hands and pull it out. You may need to wiggle it as you pull it at the same time.
- Slide in the new spout until it touches the bathroom wall.
- Secure it with the screw.
- Caulk it against the wall if need be.
- Pull up the shower diverter and turn on the water to the shower.
- Check if the problem is fixed.
This method is almost guaranteed to fix a tub faucet that leaks when the shower is turned on.
How to Replace a Threaded Bathtub Spout
- Check if the tub spout is caulked on the bathroom wall. If so, cut through the caulk with a knife.
- Use a slip-joint pliers or a wrench to loosen the spout by turning it counterclockwise.
- With the spout out, use a wire brush or an old toothbrush to clean the threads on the water supply pipe.
- Apply about 6 wraps of Teflon tape on the threads. Since you will be screwing in the spout in a clockwise direction, apply the Teflon in a counterclockwise direction.
- Thread in the spout on the water pipe starting off slowly, to avoid cross-threading.
- When the spout is hand tight, use the wrench or pliers to tighten it further. To prevent peeling off the finish from the spout, wrap duct tape or a piece of cloth on it. You only need to tighten it a little not crazy tight.
- Caulk the spout to the wall if you need to.
- Pull the shower diverter knob up and turn on the water.
- Check if the problem is fixed.
And basically that is how to fix a bathtub faucet that leaks when you turn on the shower if you have a single or double shower faucet handles.
4. Replace the Shower Diverter Valve
If you have a three valve shower diverter, the valve in the middle is usually the shower diverter. It diverts the water to the shower head or bathtub spout depending on which direction you turn the handle.
The shower diverter valve handle is connected to a stem which has a washer at the end. Turning the handle across a 180 degrees angle pushes the washer against a valve seat, which plugs off the spout and forces the water to flow out through the shower head.
When you turn the handle across a 180 degrees angle but this time in the opposite direction, the stem pulls the washer off the valve seat allowing water to flow out through the spout.
Due to friction of the washer against the valve seat, it wears off with time and hence the reason why the bathtub spout will leak when you divert water to the shower. Replacing the washer will in most of the time fix this problem.
Shower faucet manufacturers like Moen will replace the faucet for you for free. Just grab the phone and give them a call with the faucet part number. They will mail the exact replacement part to you in a few days.
While I could outline the step by step guide to replacing a shower diverter valve, I reckon a video will do just fine. Here is a good video on the same.