A leaky thermostatic shower mixer is a very common issue. They are easy to fix if you have the right parts and do it in the correct order. It is extremely important to do as much as you can to prevent leakage as soon as it is discovered.


 Tools and materials Needed

  • Replacement cartridge (comes with new bonnet and screws)
  • O-rings (sized for the valve body threads and the shower outlet)
  • Thread sealant tape or paste
  • Marking pen
  • Water supply shut off valve key or wrench
  • Rags
  • Slip joint pliers


Complete steps to repair a leaking thermostatic shower mixer:


  1. Turn off the water supply


This is done by turning the valve to the shower off, but it does not necessarily mean you are shutting off the water supply. The shower could be fed from a plumbing fixture behind the wall or under the floor. If this is an option for your home you can simply turn off that fixture. If this is not an option, use a wrench to shut off the supply at the shut-off valve located outside under a faucet if it is on your home.


  1. Drain The Valve


First, find the lowest point in your valve. Make sure it is lower than the outlet tube on the valve body. Once you have found this point, remove the cover or bonnet bolt using a wrench. You will want to flush out any sediment that has accumulated in your valve by opening the top of it which will let all the water in the valve drip out.


  1. Remove The Cartridge


Remove the cartridge from the valve by taking out the screws with a screwdriver. Once you have removed these, there will be two o-rings on either side of your thermostatic cartridge. Make sure you remove both and keep them safe for reassembly.


  1. Inspect The Cartridge


Inspect your thermostatic cartridge for any visible damage. If you see that it is badly damaged with a crack or split in the thermostat, you will need to purchase a new cartridge. Make sure to use the exact thermostatic cartridge you have removed from your old thermostatic valve so they will fit flush.


  1. Replace The O-rings


Grab the two o-rings that you removed before and place them back in the locations they came from on the thermostatic cartridge. These are used to seal up your thermostatic valve so it does not leak. When the water is turned on, these will be pushed out by pressure inside of the cartridge so they must be replaced after every thermostatic valve repair.


  1. Put The Cartridge Back Into The Valve


Replace the thermostatic cartridge and tighten down the retaining screws that were removed before onto the thermostatic valve using a screwdriver. When you put the thermostatic valve back together, these screws will put pressure against the cartridge to hold it in place and prevent leakage.


  1. Replace The Cover Or Bonnet


Replace the thermostatic valve cover or bonnet that you have removed with a wrench. You will need to tighten down the nuts on either side of the thermostatic valve stem so your thermostatic valve is watertight once again.


  1. Turn The Water On


After completing these steps, you will need to open your water supply back up by turning the main water supply valve on. Allow the thermostatic shower valve to fill up and check for any leakage around the thermostatic cartridge or where it threads into the thermostatic body before using it.


  1. Check For Leakage After Use


If you see water leakage after use, there is something wrong with your installation. If this happens, turn the thermostatic valve off immediately and fix the problem that caused the leakage to begin with. Once you have repaired it, you can re-tighten your cartridge using extra force so this does not happen again in the future.


  1. Make Sure To Use Thread Sealant


You will need to use a thread sealant on your new thermostatic cartridge so you can tighten it securely into the valve body. This is necessary to prevent leakage from occurring in the future.

 leaking thermostatic shower mixer


FAQS on repairing a leaking thermostatic shower mixer


Q: What is the difference between a thermostatic mixing valve and a thermostatic shower valve?

 A: The main difference between these two types of valves is that a shower valve will have a control on the handle, while a mixing valve allows you to mix in cold water from your supply with hot water from your heater. This helps to prevent scalding as well as saves water.


Q: What does a thermostatic shower valve do?

 A: The main purpose of a thermostatic shower valve is to control the temperature of your shower and give you an exact desired temperature. This will prevent the heater from heating the water too much and becoming scalding hot.


Q: What are the benefits of a thermostatic shower mixer?

 A: The greatest benefit is that it will prevent scalding by mixing in cold water with the hot so you do not need to worry about turning on your tap and burning yourself. Also, since they allow you to set your temperature, they help save money by stopping you from using hot water that is too hot.


Q: How do thermostatic shower valves work?

 A: thermostatic shower valves are designed to mix in cold water with the hot water coming out of your faucet. That way, they can modulate how much-heated water comes out and prevent scalding by allowing only the desired temperature to pass through.


Q: What are common problems with thermostatic shower valves?

 A: The main problem is that they can be difficult to install since your new parts must fit into older plumbing systems. Also, if they are installed improperly or leak, you will have very low water pressure in your shower which may damage your showerhead.


Q: Is it difficult to repair a leaking thermostatic shower valve?

 A: It can be, depending on how it is installed. If the water pressure is too high or if the wrong sealant has been used, it will leak and cause extensive problems. However, if you follow the steps from this guide carefully and ensure that you use thread sealant, you should have no problem repairing the leak and enjoying a new shower.


Q: Should I attempt to repair a leaking thermostatic shower valve myself?

 A: If you have some experience with plumbing or heating, likely, you can easily do this yourself. Just be sure to purchase parts that are compatible with your existing setup before attempting to install them.



Should I repair or replace a leaking thermostatic shower mixer:

 Repairing a leaking thermostatic shower mixer is possible, but the problem may occur again. Therefore, if you are not experienced with plumbing or heating problems, it might be best to replace your old parts with new ones that will not deteriorate. However, it is cheaper to repair a thermostatic shower mixer than to replace it. If you have to replace your shower system, our advice is to buy the best thermostatic shower mixer, which will at least save you the trouble of them breaking down soon.