What Is a Thermostatic Control Valve and Why Does a Tub Need One?

A thermostatic control valve, or TCV, is a mixing valve that blends the hot and cold water supplies to the temperature you set on a dial and holds it there. The tub fills at a steady temperature instead of whatever two separate handles happen to be set to. Ella walk-in tubs ordered with an Ella thermostatic faucet package include a built-in Ella TCV, and other faucet configurations do not. If your tub has one and the water still runs hotter than the setting, start with Why Is the Water in My Walk-In Tub Too Hot?.

How a Thermostatic Control Valve Works

A hot line and a cold line feed the valve, and a single mixed line runs from the valve to the spout. You set the temperature on the dial, and the valve blends the two supplies to hold it. The blending is done by a cartridge inside the valve body. When that cartridge is clean, the water at the spout stays at the setting even though two very different supplies are feeding it.

The valve body holds more than the cartridge:

• Intake screens. Screens at the water intakes catch sediment, salt and other debris before it reaches the cartridge.
• A check valve at the cold inlet. This small one-way valve sits in the housing right where the cold-water supply line connects, with a spring and a small screen in front of it. The screen catches debris from the supply, and the check valve keeps water from flowing backward through the cold side.
• Backflow protection and a high-limit stop. The spec drawing for the Ella Thermostatic Control Valve illustrates backflow prevention valves on the supply side along with the high-limit temperature stop.
• An anti-scald mechanism in the handle. This is a spring-loaded locking pin that sets against a locking collar, described in the next section.

Why a Tub Benefits from One

The first benefit is consistency. On a faucet without a TCV, the temperature is set by hand at the hot and cold valves every time you fill, and the water is only as cool as those two valves are set. With a TCV, you choose a setting once and the valve does the blending for every bath.

The second benefit is scald protection. The first video on this page shows the anti-scald mechanism inside the TCV handle. A spring-loaded locking pin sets against the locking collar, and the button must be pushed to increase the temperature. The button springs back when set at 100.4 degrees, so going hotter is always a deliberate step and never an accident. The same video shows how a plumber sets the valve internally for hotter water:

1. Remove the set screw cover and loosen the set screw with an Allen wrench.
2. Place the handle on top of the brass fitting and turn to warmer water.
3. Briefly take the handle off, then reset it, turning the handle a quarter turn counterclockwise. This allows more hot water to flow through the valve.
4. Make sure the anti-scald button is set correctly, retighten the set screw and replace the cover.

The third benefit is paperwork. Plumbing inspectors sometimes ask for literature on scald protection and backflow prevention before they approve an installation, and Ella has supplied the TCV spec drawing to municipal building departments reviewing walk-in tub projects. The related hand shower question is covered in Does the Ella Faucet Meet ASSE 1014 Backflow Requirements for the Hand Shower?.

Which Ella Faucet Configurations Have a TCV

Not every configuration has one, so check your order first. It tells you whether a TCV is present on your tub.

In practice, the thermostatic package suits a bather who wants the same temperature every time without adjusting two handles. The manual faucets suit homes where hard water would mean frequent cartridge cleaning. In areas where cleaning the cartridge becomes a recurring chore, tech support may suggest the 5-piece fast-fill faucet for that reason. Whichever faucet you have, test the water with your hand or a thermometer before entering.

Keeping a TCV Working, and What the Symptoms Mean

The cartridge inside the TCV collects calcium, iron and debris from the supply water. Once it is fouled, it can no longer hold its setting or blend properly. Fouling comes from the water supply, so an inline filter or mesh on the water lines, cleaned periodically, is required protection for the TCV. Each symptom points to a different part of the valve:

• If the water runs well above the setting, a fouled cartridge is the usual cause.
• If the water is either scalding or icy with nothing in between, the cartridge can no longer blend. See Tub Fills Only Scalding or Only Cold and Will Not Mix to Warm.
• If the faucet delivers only hot water no matter where the dial is set, while the cold line has pressure, the check valve at the cold inlet may be stuck. The steps are in Unlocking the TCV Check Valve.
• If the rest of the home loses hot water until the tub's shut off valves are closed, hot and cold are crossing inside the valve or the hand shower. See Why Does the Mixing Valve Cross Hot and Cold When the Tub Is Off?.

The second video on this page shows the service procedure from start to finish. After shutting off the water supply, the technician removes the control handle, the cover plate, the TCV governor, the washers and the escutcheon plate. The technician then unscrews the metal collar by its unthreaded flat wrench area, so the threads are not damaged, and unscrews the cartridge. The intake screens and the bottom of the cartridge are cleaned of sediment with a soft brush and some CLR. The gaskets are lightly lubricated with a lithium grease, and everything is reassembled securely without over torquing. The video also reminds you to inspect the water intake screen and the check valve on the bottom, because calcification and debris there can impede water flow.

Warranty, Labor and Documents

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 so much. When a part is covered, Ella ships it under the warranty and a local licensed plumber does the labor. Ella does not send technicians.

If the valve still overshoots after the cartridge has been cleaned, or you need documentation on the valve for an inspector, open a ticket at ellasbubbles.com/support or call (800) 480-6850. Send a photo of the faucet and valve, the measured water temperature, the setting you selected and your order details.

Related Guides

• How Do I Adjust the Maximum Temperature on a Walk-In Tub Thermostatic Valve?
• How Do I Clean or Replace the Thermostatic Faucet Cartridge?
• Temperature Control Valve (TCV) Stuck or Not Mixing: Cleaning the Cartridge and Replacing the Valve

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