Low Water Pressure in Bathtub Faucet? How to Fix It

A slow running bathtub faucet means that the water pressure in your lines is insufficient, or the water flow is being obstructed by something. The first thing therefore that you should is to determine if the problem is isolated to your bathtub or the entire house.

low water pressure in bathtub faucet

Low water pressure is a bathtub faucet is caused by clogs in the faucet cartridge, spout, and/or aerator, as result of mineral deposits and/or corrosions. It could also be caused by a stuck or partially open shower diverter.

Low water pressure in a bathtub faucet only can be caused by a partially closed or obstructed water supply valve leading to that specific fixture or by a buildup of mineral deposits and debris inside the faucet’s aerator or valve.

In a single-handle bathtub faucet, the shower diverter is the little knob at the top of the bathtub spout. It lets you select whether you want water to flow out of the tub spout or showerhead.

If the single-handle tub faucet’s shower diverter is stuck at the middle, water will not flow out of the bathtub spout with as much pressure as you would like. This is usually caused by calcium and other mineral deposits as well as rust.

For folks with a 2-handle bathtub faucet, there is usually another knob in the middle. That is the shower diverter. If it is not fully open to divert all the water out of the bathtub spout, you will notice that your tub water pressure will be low.

An aerator is an attachment at the front of some bathtub spouts with fine holes like those in your kitchen sink faucet or showerhead. Due to their small holes, it is very easy for minerals deposits or debris to clog them, significantly reducing the pressure in your bathtub.

Removing and cleaning or replacing a bathtub faucet cartridge, unclogging the aerator, and fixing a stuck shower diverter are some of the effective ways to increase the water pressure in your bathtub faucet.

How to Increase the Water Pressure in Your Bathtub Faucet.

The best way to fix this problem is to start with the easiest and if it doesn’t work move on to the next one, until you have to remove and clean or replace the faucet cartridge.  This is the order to follow:

  • Unclog the aerator
  • Open/free the shower diverter.
  • Soak the bathtub spout in vinegar
  • Replace/clean the faucet cartridge

1. Unclog the Bathtub Faucet Aerator

In your kitchen or bathroom sink faucet, you are almost guaranteed to find a small fitting at the end of the spout called an aerator. An aerator in a faucet prevents water from splashing and it also helps you to save water, as it runs for longer with less pressure.

I find having an aerator in a bathtub spout counterproductive though some tub faucets still come with them. Aerators are very easily clogged by mineral deposits and especially calcium, as well as other form of debris.

Check underneath your bathtub spout if you have an aerator in place. A faucet aerator feels like a fine mesh to the touch.

If you bathtub spout has an aerator them most likely it is clogged and that is why you are having low water pressure. This is how to fix it:

  • With your bare hand, try to loosen the aerator by turning it counterclockwise.
  • If it is too tight, use a wrench to loosen it. You should see the 2 flat edges where you are supposed to grab it with the wrench. If your spout does not have anywhere to hold with a wrench, wrap duct tape or a rag around it to prevent stripping off the finish.
  • Drop the aerator in a bowl of vinegar and wait for 20 minutes.
  • Use an old toothbrush to clean the aerator until all the holes are unblocked.
  • Open your bathroom sink faucet and blast water through the aerator to flush out all the fine particles still left in it.
  • Before connecting the aerator back, open the bathtub faucet and let water run for about 30 seconds.  This will flush out any lingering debris inside the spout.
  • Connect the aerator back to the tub spout and check for a change in water pressure.

2. Fix the Shower Diverter


Modern shower-bathtub-combos use a single-handle bathtub faucet. This single faucet controls the pressure as well as the temperature of the water. The bathtub spout also has a shower diverter that controls where the water flows out from.

If you push the shower diverter knob down, water flows out through the tub spout. To have water flowing out from the showerhead you pull the knob upwards.

In older bathrooms, you will have 3 knobs/handles. 2 of the knobs will be for selecting hot or cold water, and the temperature of each. The third knob is the shower diverter.

If someone used the shower and forgot to turn the shower diverter all the way, there will be low water pressure in the bathtub spout when someone else turns on the water from the tub faucet. Turning the shower diverter knob all the way is enough to fix this problem.

In a single-handle bathtub faucet, the shower diverter is usually inside the spout, operated by a little knob at the top of the spout. After years of usage, mineral deposits and corrosion infect the inside of the spout limiting the free up and down movement of the diverter.

When this happens, the diverter can get stuck in the middle of the spout, restricting the flow of the water and hence low water pressure in the bathtub. If this is the scenario you are in then this is how to fix it:

  • Try to pull and push the shower diverter up and down. If it feels sticks then you surely have calcium build up or rust in the spout.
  • Spray a penetrating oil on top of the shower diverter knob as well as inside the spout. Keep playing with knob and spraying more oil until the diverter becomes completely freely.
  • Another trick is to use vinegar. Fill a plastic bag with vinegar and immerse the spout in it. Secure the bag around the spout using a rubber band. Leave the setup for 12 hours or overnight.
  • Remove the vinegar and open the faucet water at full pressure for a few seconds to force out all the remaining and loosely held mineral deposits.
  • The last method you can use is to file the shower diverter grooves. Pull the knob all the way up and file the grove along which the diverter moves inside the spout to remove all mineral deposits.

3. Clean the Bathtub Spout

For people who live in areas with hard water, mineral deposits and especially calcium will build up inside your faucets. If you have had this issue with your kitchen or bathroom sink faucets, expect to have it in your bathtub faucet as well.

Your bathtub spout is usually connected to a pipe on the wall. That is the pipe that draws water from the valve

There are 2 types of bathtub spouts. There is a slip-on tub spout and a threaded tub spout. A slip-on tub spout as its name suggests is simply slid in the pipe and secure using a screw, located on its underside.

A threaded bathtub spout is usually threaded on the water supply pipe and has no screws. Bathtub spouts are sometimes caulked to the wall.

Here is how to fix a clogged bathtub spout and increase your bathtub faucet water pressure. It is a far better method than just clean the shower diverter alone. Better still, it works for diverter as well as non-diverter bathtubs.

  • If the bathtub spout is caulked to the wall cut the caulk with a putty knife.
  • If you have a slip-on tub spout, loosen the screw using an Allen wrench. Prior to removing the screw, cover the bathtub drain with a rug not to lose the screw down the drainpipe.
  • On the other hand if you have a threaded bathtub spout, wrap a tape or rag around it and loosen it with a wrench.
  • Drop the spout in a bowl and pour in vinegar until the spout is fully immersed in the vinegar. Leave it for 12 hours or overnight.
  • Use a toothbrush and emery cloth to clean the spout until all the mineral deposits are removed.
  • Before connecting the spout back to the pipe, place your hand in front of the supply pipe and blast out the water for a few seconds to flush out the debris trapped inside the pipe.
  • Connect the spout back and check for a change in water pressure.

4. Clean or Replace the Faucet Cartridge

A faucet cartridge is basically a valve connected to the handle that controls the flow of water. Depending on how much you turn the handle, the cartridge will allow more, less, or no water at all to flow out of the spout.

Just like the aerator or spout, the cartridge can also be affected by mineral deposits, limiting the amount of water flowing out through the spout and hence a low pressure.

If your bathtub spout is too old the best thing is to replace it. On the other hand if it is fairly new you should clean it in a sink and put it back inside.

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