If you've noticed a lack of hot water in your shower, it may not stem from your water heater. Instead, it may be an issue with the faucet itself. Single-handle shower configurations, as opposed to set-ups with a separate hot and cold handle, have an internal cartridge attached to a valve that mixes water from your lines to meet your desired temperature, and just like any other plumbing in your house, this system can encounter a handful of common problems. Learn what you can do to resolve these simple issues and get your hot showers back.
Step 1 - Turn Off the Water Source
Some faucets have water stop valves located on the faucet itself. Turn these (one on each line) with a large, slotted screwdriver, and then drain the remaining water from the piping by running the shower until its gone.
Tip: If the hot water stop valve is already closed for some reason, open it and see if this solves your problem.
In the event that you cannot find any stop valves, then you will need to shut off the water to the house via the water main. Drain the pipes in the shower after it is shut off until no water remains.
Step 2 - Remove the Faucet Handle
With the same screwdriver, pop off the plastic cap located at the end of the faucet handle. Inside the hole, locate the screw. Use a Philips screwdriver to loosen it, and take it out along with the handle itself. Then, pull out the metal sleeve and unscrew the backing plate. Set these aside on a towel and align them in the proper order for easier reinstallation later.
If you have a lever type handle, you may need an Allen wrench to remove it. Simple loosen the nut with the wrench and slide the handle off in a similar fashion.
Step 3 - Adjust the Temperature Limit Stop
Many single-handle fixtures have a temperature limiter (also sometimes called a rotation limit stop), which is a device that stops your handle's rotation to a "maximum" heat setting. This can be adjusted if your water just can't get hot enough.
After you've removed the faucet handle, you'll see a plastic disk and sleeve that you'll need to slide out. Pull the limit stop towards you and rotate it to the left to maximize the hot temperature; stay within an appropriate range, otherwise the limit stop will not close or return to position. Push it back to close when you're finished and reinsert the limiter back into position. Switch your water back on and test the adjustment. If it still hasn't fixed your problem, turn the water back off, empty the pipes again, and continue with the next steps.
Step 4 - Remove the Cartridge
Next, you'll want to make sure the cartridge isn't the source of the problem. Remove the temperature limiter again, and pull out the retaining clip that holds cartridge in place with a pair of needle-nose pliers.
The cartridge itself can be difficult to get out of place. Try placing the handle back on the faucet stem and using this to pull it free. If it doesn't work, some suppliers sell a specific tool for this purpose. It's also important that you make a note or take a picture of the cartridge's orientation before you remove it. Both the existing one or a new one will have to be reinstalled the same way.
Step 5 - Inspect the Old Cartridge
Check the cartridge for any damage or hard water deposits and debris that might be preventing the flow of hot water. Cartridges can be difficult to clean, but give it your best effort if you wish to save a little money.
Give this piece a shake before you consider reinstalling it as well. It should sound like shaking a spray paint can; if it doesn't, the balancing spool may be jammed. You can try to fix this issue yourself, but at this stage it will likely be easier to purchase and install a new cartridge.
Step 6 - Install a New Cartridge
Make sure you buy a new cartridge that is compatible with your model of shower faucet. Then, insert it into the valve with the same orientation as the old one. Put the retaining clip back in, followed by the temperature limiter if you have one.
Step 7 - Replace the Faucet Handle
Reopen the water valves on the faucet or on the water main and test the result of your repair. If you're successful, proceed with putting the faucet handle back in place and securing it; if not, it could be time to call a professional.