Possible symptoms:

• My shower is too hot on the coldest setting.

This post describes how to fix a shower thermostat where the coldest setting is too hot. This post is for you if:

• You have a bar shower like the one below (Doesn’t have to be the same exact model).
• You can turn the temperature dial to the coldest setting, but the water is still too hot.
• You want to fix it yourself without calling a plumber.
• You’re willing to do some relatively involved DIY work.

Note: This worked for me, but I can’t guarantee it will work for you. If you’re not comfortable with DIY plumbing, please call a professional.

You could just replace the entire shower unit, or replace the thermostat cartridge, but that has two problems:

• The cartridges are expensive, coming in at £90ish each.
• There’s lots of different types of cartridges, so you might not be able to find the right one for your shower.

In my case it was the second, so I decided to try and fix the thermostat myself. It took about 30 minutes, and cost me £10 in parts. Here’s how I did it.

Tools and Materials Needed

• Adjustable wrench
• Screwdriver (flathead and Phillips)
• Either a bench vice or you can get away with two pairs of plumbers pliers like the ones below.

• A replacement wax thermo-element like the one pictured below. I got mine from Amazon for about £10.

Note: There seems to be two type of thermo-element available. One has a screw thread and the other just sits flush. I’d advise taking yours apart using the instructions below and checking which one you need before ordering.

Here’s an example of one which is just a push fit: Push fit thermo-element

If yours is a screw thread, these seem to be a little more difficult to find on their own. But what I learned is that most of the cheap thermostats use the same thermo-element. So one thing you could do is just buy a cheap thermostat and use the thermo-element from that. Here’s the one I got for £15.

Cheap thermostat with thermo-element

Removing the thermostat from the shower

Sorry, I don’t have detailed images for this because I didn’t take them. This video is pretty good though.

1. Turn off the water supply to the shower. This is usually done by turning off the main water supply to your house. Alternatively if your shower has a shut-off valve, you can use that.
2. Remove the temperature control knob from the bar. This is normally completed by:
   1. Removing the face plate from the knob with a flat head screwdriver.
   2. Removing the screw with a phillips head screwdriver.
3. Remove the plastic safety mechanism from the spline on the end of the thermostat.
4. Now you have what seems to be two configurations:
   1. A grub screw holding the thermostat in place. If it’s a grub screw then remove the screw and then remove the thermostat.
   2. A Threaded nut with two keyways cut into it. IF this is the case then knock the keyways with a screwdriver, remove the nut by unscrewing then the thermostat should lift out.

At the end of all this, you should have a thermostat which looks something like the one here:

Stripping the thermostat

The next stage is to strip the thermostat down. Firstly, clamp the side of the thermostat which is as far way from the toothed spline in either a vice or your plumbers pliers. Then clamp the larger of the two toothed splines in your other pair of pliers (see image below.)

Then, you’ll want to turn anti-clockwise. So If you have clamp 1 in your left and clamp 2 in your right hand, turn clamp 2 down.

Now you’ve loosened the body, continue to unscrew until the two parts come apart. Be careful here because there’s a slight spring action, don’t lose any parts.

You should now have something like the image below. Don’t worry if it doesn’t look exactly the same, different designs split in slightly different places.

Now, take the lower half (the fat end which does not have the splines) and remove the inner components. You should see:

• A spring.
• A piston.

Ignore the rest of it for now, and take a look at the piston. This is actually formed of two components:

1. The piston itself.
2. The wax thermo-cartridge.

You should be able to remove one from the other. They will either just pull apart or unscrew. Use your vice or plumbers pliers again to unscrew one from the other.

Now you have the whole thing apart. Use the information at the top of this article to find a replacement thermo-cartridge which matches yours. Pay attention to the screw vs push fit. Once you have a replacement one of these, simply replace your old one, and follow these steps backwards to re-assemble your shower!

Common Symptoms and Search Terms

If you’ve landed here because your shower’s been trying to boil you alive, you’re not alone. These are the kinds of problems people search for when their thermostatic mixer shower isn’t working properly:

• Shower too hot on coldest setting
• Thermostatic shower always hot
• Shower stuck on hot even when set to cold
• Mixer shower won’t go cold
• Shower only giving hot water
• Thermostatic shower temperature not adjusting
• Shower temperature stuck hot
• Bar mixer shower too hot
• Mixer valve not mixing properly
• Faulty thermostatic cartridge symptoms
• Shower not mixing hot and cold water
• Thermostatic valve stuck or broken
• Wax element in shower mixer not working
• How to fix thermostatic shower cartridge
• Replace shower mixer thermostat
• DIY thermostatic shower repair
• Shower runs hot no matter the setting
• Thermostatic shower valve fix
• Shower too hot cheap fix
• How to fix shower that won’t cool down
• My shower is too hot even on cold
• Shower temperature control broken
• Shower cartridge failed
• Can I fix shower mixer myself
• Bar shower too hot no cold
• How to replace wax thermostat in shower
• Shower repair no plumber

If you’re dealing with any of the above, this post walks through how I diagnosed and fixed a faulty wax thermostat inside a bar mixer shower — without replacing the whole unit.