Why Does the Mixing Valve Cross Hot and Cold When the Tub Is Off?

When the mixing valve mixes hot and cold when the tub is off, you have a crossover: hot and cold are meeting somewhere in the tub's plumbing and pressure from one side is pushing into the other, which is why the whole suite loses hot water until you isolate the tub. On an Ella tub the first place this happens is a worn or fouled thermostatic cartridge in the temperature control valve, fixed by cleaning or replacing the cartridge. The second is the hand shower, whose blue check valve and hose orientation are the other crossover path. The first thing to check is whether closing the tub's shut off valves restores hot water elsewhere, which confirms the tub is the source.

Likely Causes

• A thermostatic control valve cartridge fouled by calcium, iron or sediment so it no longer seals between hot and cold.
• A missing or failed check valve at the hand shower head, or a hose installed backwards.
• No inline filter or mesh on the water lines, letting scale reach the cartridge.

What to Check, in Order

1. Confirm the source. Close both shut off valves at the tub. If the rest of the home's hot water comes back, the crossover is inside the tub's faucet or hand shower.
2. Check the hand shower head. Inside the threads sits a small blue backflow prevention check valve. If the threads show an empty hole, the head is replaced. Also confirm the hose orientation, conical end at the handset and hex nut at the deck mount, as shown in hand shower hose orientation and the check valve.
3. If the hand shower is fine and your faucet has a thermostatic control valve, clean the cartridge. Shut off the water, remove the handle and escutcheon, unscrew the collar and cartridge, and clean the intake screens and cartridge of calcification. Reassemble without over torquing. The full procedure is in TCV cartridge cleaning and replacement.
4. If cleaning does not stop the crossover, replace the cartridge. The TCV carries a 1 year limited warranty separate from the lifetime parts warranty, and fouling from contaminated water is not covered.
5. Fit and clean an inline filter or mesh on the water lines so scale does not foul the new cartridge. That protection is required for the TCV.
6. Open both shut off valves fully and confirm the fill temperature responds normally. Valve placement is in water supply lines and shut off valves.

The video walks through shutting off the water, removing the control handle, governor and escutcheon, unscrewing the collar and cartridge, cleaning the intake screens and check valve with a soft brush and CLR, lightly greasing the gaskets and reinstalling without over torque. Removal and cleaning should be done by a licensed and insured plumber. Watch: Ella's Bubbles: TCV Valve Replacement with chapters and a full transcript.

When to Open a Ticket

If the crossover continues after the hand shower check and a cartridge cleaning, open a ticket at ellasbubbles.com/support with your serial number, which faucet set you have, photos of the cleaned cartridge, intake screens and hand shower head threads, and whether an inline filter is fitted. Your Ella dealer or the team at (800) 480-6850 confirms whether your configuration includes a TCV and arranges the cartridge or head you need.

Related Guides

• Cold Water Reaches the Tub but Will Not Come Out of the Faucet: Unlocking the TCV Check Valve
• Does the Ella Faucet Meet ASSE 1014 Backflow Requirements for the Hand Shower?
• How Do I Clean or Replace the Thermostatic Faucet Cartridge?
• What Is a Thermostatic Control Valve and Why Does a Tub Need One?

Common Questions