Quick Answer:

If your tub suddenly has no cold water, start by checking other faucets to see if the problem is local to the tub. Often it’s a stuck internal cartridge, a blocked cold inlet, or a safety stop set wrong. If the whole house has no cold, check the main valve and call a plumber if you’re unsure.

Why This Happens

• Single-handle mixer valves use an internal cartridge. If the cold side of that cartridge fails or gets clogged, only hot water will flow.
• Some faucets have an anti-scald or temperature stop. If that is set too far toward hot, it may prevent cold from mixing in.
• Cold-side supply valves or shutoffs under the tub can be closed or partially blocked by sediment.
• Less common: a problem with the home’s cold supply (frozen pipe, closed main) affecting multiple fixtures.

Step-by-Step What to Do

1. Test cold water at other fixtures

• Run a cold tap at the kitchen sink and a cold tap at a bathroom sink. Note whether they produce cold water and how strong the flow is.
• If no cold water is available anywhere, shut off sensitive appliances and locate your main water shutoff valve. If you can’t restore cold, call a plumber or your water provider.

2. Check the tub handle alignment

• Move the handle slowly between cold and hot. Does the handle reach the full cold position or stop early? Some handles only move partway and can be misaligned after removal or servicing.
• If the handle is loose or rotated incorrectly, tighten the set screw or remount the handle so the full cold range is reachable.

3. Inspect anti-scald / stop settings

• Many modern tub valves include an adjustable stop that limits how far toward hot the handle can go. Remove the handle and trim to view the stop mechanism (consult the valve’s manual or a photo before adjusting).
• If the stop is set too far toward hot, back it off a bit and test. Make small changes and test flow each time.

4. Check nearby shutoff valves and supply

• Look under access panels or behind the tub for cold-side shutoff valves. Ensure they are fully open (turn counterclockwise until they stop).
• Partial closures, valving work, or debris can reduce cold flow even when the handle is working.

5. Consider cartridge failure or a cold-side blockage

• If other fixtures are fine and the stop is correct, the internal cartridge or mixer may be damaged or clogged on the cold side. This is a common cause when the tub only gets hot.
• Replacing the cartridge or cleaning the inlet screens usually fixes the problem. If you’re comfortable, turn off water, remove the cartridge, inspect for mineral buildup, and replace if worn. Otherwise call a plumber.

6. Temporary measures while you wait

• Use another bathroom for bathing if the tub water is too hot.
• A controlled mix from a sink may be faster for filling a small container for rinsing instead of adjusting a stuck tub valve.

What Not to Do

• Do not force the handle. Forcing can break the valve, the handle, or the cartridge and make repairs more expensive.
• Do not keep running scalding water in the tub trying to “burn off” the problem. That risks burns and wastes water.
• Do not assume it will fix itself. Valve failures and blockages usually need intervention.

When to Call a Professional

• Call a plumber if multiple fixtures have no cold water after you test them, or if you can’t access or identify the shutoffs.
• If you suspect a worn cartridge, damaged mixer, or a seized valve, a plumber can diagnose and replace parts with the right model.
• If you find signs that the valve or piping is leaking, corroded, or possibly a shutoff valve stuck or broken, stop and call a professional to avoid water damage.

Safety Notes

• Always shut off the water supply before disassembling a faucet. Use local shutoffs or the main if needed.
• Test water temperature carefully. Run cold first and avoid placing hands directly in very hot water.
• If you smell gas, see severe corrosion, or encounter wiring near the valve, stop and call a pro—do not proceed.

Common Homeowner Questions

• Q: Why does the tub get hot but the sink in the same bathroom is fine?
  A: The tub has its own valve cartridge and supply lines; a failure or blockage can be limited to that fixture.
• Q: Can I replace the cartridge myself?
  A: Yes if you’re comfortable shutting off water and following manufacturer steps, but keep the part number handy or call a pro if unsure.
• Q: How long will a cartridge last?
  A: With normal use, several years; mineral buildup, hard water, and heavy use shorten life and can cause cold-side failures.