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Tub Fills Only Scalding or Only Cold and Will Not Mix to Warm

Updated September 2026

▶Glossary9
  1. How the Valve Is Supposed to Work
  2. Clean or Replace the Cartridge
  3. Switching to a Manual Fast-Fill Faucet
  4. Warranty and Who Does the Work
  5. Help Support Find Your Tub
  6. Related Guides
  7. Related Videos
  8. Common Questions
  9. Still Need Help?

When the water from your tub's faucet is either scalding or icy and no handle position gives you warm water, and your tub has an Ella thermostatic faucet package, the usual cause is the thermostatic control valve (TCV) rather than a plumbing mistake. The cartridge inside the TCV collects calcium, iron and debris from the supply water, and once it is fouled it can no longer blend hot and cold. The fix is to clean the cartridge, replace the cartridge, or replace the whole TCV.

How the Valve Is Supposed to Work

A hot line and a cold line feed the valve, and a single mixed line runs to the spout. You set the temperature on the dial and the valve blends the two supplies to hold it. Our overview of what a thermostatic control valve does explains the parts involved. When the water jumps between the two extremes with nothing in between, the cartridge is the first thing to check.

Clean or Replace the Cartridge

  1. Shut off the hot and cold supplies to the tub.
  2. Remove the TCV cartridge. Support can send a video that shows how to retrieve it and clean it.
  3. Clean the cartridge of scale and debris, reinstall it and test. If the water still will not mix, replace the cartridge with a new one.
  4. If the valve itself has failed, replacing the whole TCV is the recommended repair. See replacing an older TCV for supply sizes and what is included.

Because fouling comes from the water supply, fit an inline filter or mesh and clean it periodically. Our guide to protecting the TCV from hard water covers the filter and cleaning schedule.

Switching to a Manual Fast-Fill Faucet

If cleaning the cartridge becomes a recurring chore in your area, tech support may suggest replacing the thermostatic faucet with the Ella 5-piece fast-fill faucet. It mixes with manual hot and cold handles and has no thermostatic cartridge to foul, which minimizes maintenance. Read how the fast-fill faucet handles temperature before deciding, because it does not hold a set temperature on its own. Your Ella dealer or the team at (800) 480-6850 can help with that change.

Warranty and Who Does the Work

The TCV carries a 1-year limited warranty and is excluded from the lifetime parts warranty. Cartridge fouling caused by calcium, iron or contaminated water is not a covered defect, which is why the inline filter matters. When a part is covered, Ella ships it under the warranty and a local licensed plumber does the labor. Ella does not send technicians. Tech support will call you to talk through the diagnosis, so include the best number to reach you.

Help Support Find Your Tub

If your warranty was activated after installation, support can locate your tub by serial number. If it was not, or if you bought the home with the tub already installed, have the model, where the tub was purchased and the approximate purchase date ready. Send photos of the faucet and of the valve so tech support can see what is installed before anything ships.

Chapters in this video
  1. 0:00 Remove Control Handle And Cover The technician removes the control handle and cover plate after shutting off the water supply.
  2. 0:16 Remove Escutcheon Plate And Collar The technician removes the washers, escutcheon plate, and then unscrews the metal collar.
  3. 0:33 Unscrew Cartridge And Clean Screens The technician unscrews the cartridge and cleans the intake screens and cartridge bottom.
  4. 0:56 Replace Cartridge And Reassemble The technician lubricates and replaces the cartridge, then reassembles the collar, escutcheon plate, and control handle.
  5. 1:30 Inspect Water Intake Screen The technician inspects and cleans the water intake screen and check valve for calcification and debris.

Common Questions

Did my plumber install the faucet valve incorrectly?
Usually not. The hookup is a hot line, a cold line and one mixed line to the spout, and the most common cause of the hot-or-cold symptom is a fouled cartridge, which happens even on a correct installation. Send photos of the faucet and valve so tech support can confirm.
Can I clean the TCV cartridge myself at home?
Yes. Support can send a video that shows how to remove and clean the cartridge. Shut off the supplies first, and if cleaning does not restore warm water, plan on a new cartridge or a new valve.
Is the thermostatic control valve covered by warranty?
The TCV has its own 1-year limited warranty rather than the lifetime parts coverage. Fouling from mineral-laden or contaminated water is not covered, so fit and clean an inline filter to protect it.
Can I replace only the cartridge instead of the whole valve?
Yes. The cartridge can be replaced on its own when cleaning does not help. When the valve itself has failed, replacing the whole TCV is the recommended repair.
Should I just replace the whole faucet instead?
If the valve has failed, replacing the whole TCV is the recommended repair. If fouling keeps returning, switching to the 5-piece fast-fill faucet with manual mixing is an option to discuss with your Ella dealer or the team at (800) 480-6850.
What information does support need to locate my tub?
The serial number is enough if the warranty was activated after installation. Otherwise, provide the model, where the tub was purchased, the approximate purchase date and your contact number so tech support can find the unit and call you.

Still Need Help?

Open a ticket at ellasbubbles.com/support or call (800) 480-6850 and have your model and serial number ready.

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