Why Does My Ella Thermostatic Faucet Only Run Lukewarm Water?

When an Ella thermostatic faucet only runs lukewarm water no matter where you set the dial, the usual cause is the thermostatic control valve (TCV) cartridge fouled by calcium, iron or sediment, so it can no longer blend the full hot supply into the mix. A valve stuck on lukewarm is the same fouled-cartridge problem described in Why Is My Tub's Temperature Control Stuck or Not Changing the Water Temperature?, seen from a different angle. Before a plumber pulls the cartridge, though, rule out the two house-side causes that produce the same lukewarm result: a hot shutoff valve that is only partly open, and a water heater that cannot deliver hot water at the flow rate of an Ella fast-fill spout.

Why a Thermostatic Faucet Ends Up Lukewarm

A hot line and a cold line feed the valve, and a single mixed line runs to the spout. You choose a temperature on the dial and the cartridge blends the two supplies to hold it. Lukewarm water means the blend is heavy on the cold side, and that happens in three ways.

• The cartridge is fouled. Scale and sediment on the cartridge and its intake screens stop the hot side from mixing through. This is the same cause behind a valve that gives only cold, only hot, or stays lukewarm wherever the handle sits.
• The hot side is restricted. A hot supply shutoff that was never fully opened at installation, a kinked supply line behind the tub, or a valve or filter an installer added to the hot line all starve the valve of hot water. Anything added between the hot valve and the faucet affects only the hot side.
• The water heater cannot keep up. The 5-piece fast-fill set flows up to 18 gallons per minute and the 2-piece set up to 16 gallons per minute at 60 PSI with ideal plumbing. A tank heater supplies stored hot water at any flow rate, but a tankless heater has to heat water as it passes, and if the spout draws more than the heater can warm, the outlet temperature drops.

One more thing to set aside is the in-line heater. The video shows what it does: once you have filled the tub at a comfortable temperature and started the hydro massage, the heater works with the water pump to hold that temperature. It does not heat cold water and it does not run without the pump, so it cannot make a lukewarm fill any warmer.

What to Check, in Order

1. Confirm your faucet has a TCV. Your order tells you which package the tub shipped with. The dual-lever 5-piece fast-fill faucet is not thermostatic, and there is no filter, aerator or thermostatic control inside its hot and cold valves, so whatever temperature is in the supply line is what reaches the spout. On that set a lukewarm fill points at the house supply, an added valve, or the size and recovery of the water heater.
2. Open the access panel and check both shutoff valves. A valve that is only cracked open lets hot water reach the faucet without passing through in useful volume. Open both fully.
3. Look along the hot supply line. Check for a kink, and for any valve or filter that was added at installation between the house line and the faucet.
4. Compare the tub with the sinks. If the sinks run fully hot and the tub does not, the cause sits between the house line and the spout, not in the water heater. Why Is There No Hot Water at the Tub When the Sinks Have Hot Water? works through that case.
5. Test the hand sprayer and the spout separately. They cannot run at the same time, so try each on its own at full hot. The sprayer passes a small amount of water, while the spout flows far more. If the sprayer is hot and only the spout is lukewarm, the difference is created after the hot valve: the diverter, an added fitting, or a heater that cannot keep up with the spout's flow. That pattern is covered in Hand Sprayer Runs Hot but the Tub Spout Is Only Lukewarm: What to Check.
6. Note your water heater type and rating. A tankless heater feeding a walk-in tub should be rated 11 gallons per minute or higher, and a 75 gallon or larger tank is recommended. Compare a tankless rating with the flow of your faucet set.
7. Notice whether the fill is slow as well. Scale on the TCV intake screens or the check valve at the bottom of the cartridge chokes flow to a trickle even when the water is hot. Lukewarm water together with a fill that runs well past 15 minutes is a strong sign the screens are clogged, as explained in Why Does My Walk-In Tub Fill So Slowly?.

Cleaning or Replacing the Cartridge

If the shutoffs are open, the sinks are hot and the heater is adequate, the cartridge is next. Shut off both supply valves to the tub and have a licensed and insured plumber do the work.

1. Loosen the allen bolt and lift off the handle, then remove the cover plate.
2. Slide off the governor, remove the washers and the escutcheon, and unscrew the collar using only its flat wrench area.
3. Unscrew the cartridge. Clean the intake screens and the bottom of the cartridge, including the check valve, with a soft brush and a lime scale remover such as CLR, or fit a new cartridge.
4. Lightly grease the gaskets with lithium grease and reassemble without over tightening. Put the governor and limiter back in their original orientation, because a governor that goes on turned can send hot water through with the handle in the cold position.
5. Turn the water back on and test the full range of the handle.

If the water still will not mix after cleaning, replace the cartridge, and if the valve itself has failed, replace the whole TCV. Tub Fills Only Scalding or Only Cold and Will Not Mix to Warm explains that choice. Because the fouling comes from the supply water, fit an inline filter or mesh on the supply lines if there is not one already, and clean it on the same monthly rhythm as your vinegar flush.

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. 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, which mixes with manual hot and cold handles and has no cartridge to foul, though 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.

When to Open a Ticket

If both shutoffs are open and the faucet still delivers only lukewarm water, open a ticket at ellasbubbles.com/support with your serial number, a photo of the faucet set on the deck, a photo of the shutoff valves and supply lines behind the access panel, a note on whether the tub has a thermostatic valve and whether an inline filter is fitted, and your water heater type and rating. Tech support will call you to talk through the diagnosis, so include the best number to reach you. Any part comes through your Ella dealer or the team at (800) 480-6850.

Watch: Ella's Bubbles: In-line Water Heater Maintains Comfortable Water Temperature with chapters and a full transcript.

Related Guides

• Temperature Control Valve (TCV) Stuck or Not Mixing: Cleaning the Cartridge and Replacing the Valve
• Faucet drips or the handle feels stiff: replacing your faucet cartridge step by step
• Hard Water and Your Tub: Protecting the TCV with an Inline Filter and Preventing Mineral Damage

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