No Hot Water in One Faucet or Shower

First: one fixture or the whole house?

Run hot water at the kitchen sink, a bathroom sink and the tub. If every hot tap is cold or lukewarm, the problem is the water heater, and you want no hot water: why your water heater stopped heating. If only one fixture is cold, keep reading.

Shower or tub: likely causes

1. 1

   Cause 1: A worn or stuck cartridge

   Single-handle showers mix hot and cold inside a cartridge. Most modern ones are pressure-balancing: a spool inside shifts to keep the temperature steady when someone flushes a toilet. When that spool sticks with scale or debris, it can block the hot side and leave you with cold water only. Moen's support pages list "No HOT (just cold) water on tub shower units" as one of their common troubleshooting cases, and note that a shower that sits unused for a while can start giving only hot or only cold.

   Sometimes working the handle back and forth frees it. Usually the cartridge needs cleaning or replacement. Buy the exact cartridge for your valve brand and model.

2. 2

   Cause 2: The rotational limit stop

   Most single-handle valves have an anti-scald limit stop that sets how far the handle can turn toward hot. If it's set too far toward cold, or someone moved it during a repair, the shower never gets fully hot even though the heater is fine. Pull the handle and trim plate and you'll see a plastic stop or a toothed ring. Rotating it a notch or two toward hot lets the handle travel farther. Adjust in small steps and test each time.

3. 3

   Cause 3: Hot and cold reversed

   After a cartridge replacement, a reversed cartridge can make the hot side behave like the cold side, and a shower that "has no hot water" turns out to be hot at the far end of the handle travel. Moen's FAQ covers this case for its Moentrol showers. The fix is usually to rotate the cartridge or its stem per the maker's instructions.

4. 4

   Cause 4: Debris in the valve or shower head

   After plumbing work or a water main repair, grit can lodge in the hot inlet of the valve. A clogged shower head reduces flow but rarely kills only the hot side. Pull the cartridge and flush the valve body briefly with the water on (carefully, into a bucket) to clear debris.

5. 5

   Cause 5: A frozen hot water line

   If it's winter, the shower is on an outside wall, and the hot water quit suddenly overnight, the hot line may have frozen. Hot lines can freeze before cold ones because they sit unused longer. Warm the area gently and call a plumber if you suspect a split pipe.

Kitchen sink with no hot water

When only the kitchen faucet runs cold:

• Check the shutoff under the sink. Someone may have closed the hot supply stop. Open it fully.
• Clean the aerator. Unscrew the tip of the faucet and rinse out debris.
• Look at the cartridge. Single-handle kitchen faucets use cartridges too, and a stuck one can block the hot side. Moen's FAQ also covers kitchen and bath faucets with reversed hot and cold.
• Check the supply line. A kinked or clogged hot supply hose under the sink can cut flow.

With a tankless water heater, a kitchen faucet run at a low trickle may not move enough water to switch the heater on, so you get cold water. Open the faucet further. If hot water reaches the shower but never the sink, the faucet is still the likely suspect.

Fixing a shower with no hot water: the steps

1. Turn off the water to the shower at the valve stops or the main.
2. Pop off the handle cap, remove the handle screw and the handle, then the trim plate.
3. Check the limit stop. If it's set toward cold, adjust it and test before you go further.
4. Pull the retaining clip and remove the cartridge. Note its orientation.
5. Inspect for scale, debris or damage. Clean it, or swap in a new matching cartridge.
6. Reassemble, turn the water back on and test the full temperature range.

If the valve is an older two- or three-handle model, the problem is often a worn stem washer or seat on the hot side, which is also a fairly simple swap.

When to call a plumber, and what it costs

Call a plumber if the cartridge is seized in the valve body, the valve is an old model with no parts available, or you suspect a frozen or broken pipe in the wall. HomeGuide notes a minimum service call fee of $50 to $200 in many areas, and a cartridge swap is often a short visit. Replacing a whole shower valve takes wall access and costs a good deal more.