If your thermostatic shower has started to malfunction, you may need to replace the thermostatic valve mechanism that regulates the flow of water and the water's temperature.
Fortunately, the mechanics of how a thermostatic shower operates are fairly similar to how any other shower functions. With a bit of work, you should be able to repair your thermostatic shower yourself in no time.
Step 1 - Remove Handle
Using a flat-head screwdriver, you will remove the cap off of the handle on your shower to expose a Phillips-head screw beneath. Unscrew this screw to remove the handle from your shower. Beneath this, you will look for another screw for the lever handle itself. Once you have located this, unscrew it and remove it as well.
Step 2 - Remove Shower Handle Faceplate
Once you have removed the handle, you will need to remove the actual handle faceplate from the wall. As you remove parts, keep track of the order they were assembled, as you will need to reassemble these pieces again when you put the shower back together.
Step 3 - Turn off Water
Once you have removed the faceplate to the shower handle, you should have a hole in your wall through which you can see the shower valve. If there are stop-check valves at the point where the hot and cold water supplies enter the thermostatic valve, turn these so that the water is shut off.
If these stop-check valves are not present in your system, you will need to turn off the water to the bathroom you are working in, or possibly to the entire house.
Step 4 - Remove Thermostatic Cartridge
Once you have exposed the thermostatic valve mechanism, you will need to remove the cartridge in the unit. There should be a U-shaped retainer mechanism that can usually be removed by gripping it with pliers and dislodging it. In other units, there will be a series of nuts and bolts that must be loosened before the cartridge can be removed.
Step 5 - Disconnect Thermostatic Mechanism
Next, you will need to disconnect the thermostatic mechanism entirely from the water supply and from the shower hose and head. There will be both hot and cold water supply pipes that must first be disconnected from the thermostatic shower valve. Turn these with a wrench to disconnect them.
If the connectors are recessed deeply into the wall, you may need to use a deep socket wrench to reach them. Next, you will need to disconnect the valve from the hose and showerhead above the unit. To do this, use a similar technique to the one described above for the hot and cold water supplies.
Step 6 - Install New Thermostatic Shower
After purchasing a compatible thermostatic shower unit, you will need to reattach the hot and cold water supplies and attach the shower hose and head to the valve itself. If you turned off the water supply using the stop-check valves on the hot and cold water supplies, be sure to open these at this point.
Reassemble the shower faceplate and the shower handle and test to make sure your new unit is working properly.