Shower Not Getting Hot? Why It Runs Cold or Lukewarm
When the sinks get hot water and the shower does not, the cause is in the shower valve: the temperature limit stop, a handle or cartridge put in out of position, or a worn pressure-balance or thermostatic cartridge. How to work through it in order.
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Short answer. If the sinks get hot water and the shower does not, the problem is in the shower valve, not the water heater. Work through it in order: the temperature limit stop under the handle, then whether the handle or cartridge was put in out of position, then the cartridge itself. On older valves a worn or stuck cartridge is the most common cause, and a new one restores the full range.
Is it the shower or the whole house?
Run hot water at the bathroom sink.
- The sink is hot. The water heater is fine. The problem is in the shower valve.
- Nothing in the house is hot, or everything goes cold after a few minutes. That points to the water heater, and no shower part will fix it.
Read the symptom
| What you see | What it usually means | What to do next |
|---|---|---|
| Handle stops well short of full hot | Limit stop set too low | Move the stop toward hot, check with a thermometer |
| Got cooler when the weather turned cold | Colder incoming water, same stop setting | Reset the limit stop |
| Hot and cold reversed | Cartridge or handle installed out of position, or supplies reversed in the wall | Rotate per the maker’s instructions |
| Cold no matter where the handle is | Pressure-balance spool stuck, or a failed cartridge | Replace the cartridge |
| Temperature swings when a toilet flushes | Pressure-balance cartridge worn or sticking | Replace the cartridge |
| Slow to change, or stuck at one temperature, on a valve with separate temperature and volume controls | Scaled thermostatic element | Replace the thermostatic cartridge |
| Full flow, temperature never changes, right after a new cartridge | Cartridge not seated on its locating pins, or wrong part | Reseat it; compare the face to the old one |
Step 1: the temperature limit stop
Most single-handle showers have an adjustable stop under the handle that limits travel toward hot. Moen’s first check is simple: does the handle reach the full hot position? If it stops short, the stop needs repositioning. The idea is the same on most brands: handle off, pull the stop, move it a notch toward hot, test.
Always check with a thermometer in the stream. Manufacturers recommend no more than 120 degrees Fahrenheit at the outlet, and some codes set it lower. Never run the valve with the stop removed.
Step 2: position
If hot and cold feel reversed or the range is cut off at both ends, something went in out of position, which is common right after a repair. Moen lists a handle mounted upside down as one cause. Many single-handle shower cartridges also have a correct rotation, and makers publish how to turn the cartridge or stem when the hot and cold supplies are reversed in the wall. Follow the instructions for that valve rather than guessing.
Step 3: the cartridge
There are two kinds, and they fail differently.
Pressure-balance cartridges have a spool or a diaphragm that shifts to keep the temperature steady when someone flushes a toilet. When scale makes it stick, the shower runs cold, lukewarm, or swings. Moen’s guidance for a valve that still will not get hot after the other checks is to replace the cartridge and flush the valve body.
Thermostatic cartridges use a wax element that expands with heat. You will usually see a separate volume control. When the element scales up, the valve responds slowly or sticks at one temperature.
Either way, pull the whole cartridge to identify it. The stem alone is not enough on these.
What to do next
- Shut off the water at the shower stops or the main, and open the shower to drain it.
- Remove the handle and check the limit stop first. Many showers are fixed right here.
- If the cartridge is the cause, pull it, noting its rotation and orientation, and replace it with an exact match.
- Seat the new one by hand until it drops flush on its pins, then fit the nut or clip.
- Reset the limit stop with a thermometer.
Removal steps by brand: Moen, Delta, Kohler, Pfister, American Standard.
The valve is hidden and the trim tells you nothing
Shower valves are the hardest fixtures to identify from the outside: the valve is in the wall, and the trim is often a different brand from a later remodel. Photograph the handle, the trim plate and the cartridge face and a specialist identifies the valve and the cartridge. More in shower cartridge identification.
When to call a plumber
Call a pro if the water heater is the cause, if the cartridge is seized, if there are no stops and the main will not close, or if a thermostatic valve has built-in checks and settings you are not comfortable resetting.
Common questions
Why does my shower only run cold when the sink has hot water?
If other fixtures get hot water, the water heater is fine and the problem is in the shower valve. The usual causes are a temperature limit stop set too low, a handle or cartridge installed out of position, or a worn or stuck cartridge.
What is a shower temperature limit stop?
An adjustable stop under the handle that limits how far it turns toward hot, there to prevent scalding. If it is set conservatively, or the incoming water gets colder in winter, the shower may never get comfortably hot.
Why did my shower get colder in winter?
Incoming water is colder in winter, so the same handle position mixes to a cooler temperature. Moen notes that seasonal changes in incoming water temperature change the maximum shower temperature, and Delta notes some valves need the limit stop reset between seasons.
Can a bad cartridge make a shower run cold?
Yes. A pressure-balance cartridge has a sliding spool or a diaphragm that balances hot and cold. If scale makes it stick, the shower can run cold, lukewarm, or swing in temperature. A thermostatic cartridge with a scaled up element can respond slowly or stick at one temperature. Either way the fix is a new cartridge.
I put in a new cartridge and now the water will not change temperature. Why?
Check that the cartridge is fully seated. Many shower cartridges have small locating pins that must drop into holes in the valve body. If a pin sits on the face instead, the cartridge rides high, water bypasses it, and the retaining nut can still feel tight. Pull it, find the holes, and make sure it drops flush by hand before the nut goes on.
Is it safe to set the limit stop all the way to hot?
Set it with a thermometer, not by feel. Manufacturers recommend no more than 120 degrees Fahrenheit at the outlet, and local codes may be stricter. Never run the valve with the stop removed.