Quick Answer:
If your shower only gives cold water, first check a nearby sink to see if hot water is available there. If the sink has hot water, the shower valve or cartridge is the likely cause. If the sink is cold too, the problem is usually the water heater or its controls. Follow the steps below to narrow it down safely.
Why This Happens
There are two broad causes:
- Plumbing valve or cartridge issue at the shower (stuck cartridge, debris, or internal anti-scald stop).
- A problem with the water heater or the supply of hot water (no pilot, tripped breaker, heater shutdown, or sediment build-up reducing output).
Other triggers include recent water shutoffs or repairs, which can introduce air or debris into lines. If the heater was recently turned off or shut off for work, see whether the unit is running — this is often the first place to check for a water heater not working.
Step-by-Step What to Do
1. Check hot water at a nearby sink
Turn the hot tap fully open at a sink near the shower and let it run for 30–60 seconds.
- If the sink produces steady hot water, the issue is almost certainly the shower valve or cartridge.
- If the sink is also cold or only lukewarm, proceed to check the water heater.
2. Run the shower on full hot to observe behavior
Set the shower control fully to the hot side and note:
- Is there any flow at all, or is it very low? Low flow can mean a blockage or sediment in the cartridge.
- Does temperature change over time (gets hotter or stays cold)? If it slowly warms, it could be trapped air or the heater just recovering.
Avoid repeated aggressive switching between cold and hot; that can cause sudden scalding if the heater comes on.
3. Confirm the water heater is operating
Check these heater basics:
- Gas heater: Is the pilot light on? Any error lights on the control panel?
- Electric heater: Is the breaker tripped? Any visible fault lights or recent power outages?
- Thermostat: Is the thermostat set to an appropriate temperature (120–125°F recommended)?
If you recently had a water shutdown or the heater was turned off, allow time for recovery; household systems can take time for hot water and pressure to return to normal. If you need guidance on recovery timing, read about how long it takes for water pressure to normalize.
4. Check the anti-scald or temperature limit stop
Many single-handle mixers have an anti-scald stop or adjustable limit screw that prevents full hot. Consult the shower manufacturer’s quick guide (or the visible stop behind the handle) to see if the limit was moved. Do not remove the cartridge or access the valve while the water is under pressure.
5. Consider a hot-side blockage or cartridge problem
If the sink has hot water but the shower does not, the cartridge or the hot inlet to the mixer may be blocked by mineral scale or debris. Typical signs:
- Cold-only when handle is toward hot but sinks are hot.
- Uneven flow or sputtering on hot side only.
Fixes often include replacing or cleaning the cartridge and flushing debris from the lines. Because this can involve shutting off the water and removing the cartridge, it’s a good point to call a plumber if you’re not comfortable with the work.
What Not to Do
- Do not disassemble the valve while the water supply is still on or the system is under pressure.
- Do not keep testing hot settings repeatedly until you risk scalding yourself or others.
- Do not ignore other signs of water heater failure, such as leaks, unusual noises, or no hot water at any tap — these can indicate a serious problem.
When to Call a Professional
Call a licensed plumber or HVAC technician if any of the following apply:
- No hot water at any fixture after checking the heater basics, or the heater shows fault lights.
- You suspect a gas pilot, burner, or electrical issue with the water heater.
- The shower valve needs cartridge replacement and you’re unsure how to isolate the water and reassemble it safely.
- There’s a leak behind the wall, visible corrosion, or a strong sulfur/gas smell.
Safety Notes
- Turn off electrical power at the breaker before inspecting an electric water heater. For gas heaters, do not attempt internal repairs — a qualified technician should handle gas components.
- Shut off the water supply to the shower before removing handles or cartridges to avoid pressurized spray.
- Use caution with temperature changes; limit tests to brief checks and avoid full exposure until temperature is confirmed safe.
Common Homeowner Questions
- Why does the sink have hot water but the shower is cold?
Most often a blocked or failed shower cartridge or an internal valve issue at the shower. - Could a recent water shutoff cause this?
Yes — air, debris, or pressure changes after a shutoff can reduce hot flow until the system clears. - How fast can a water heater recover after being turned back on?
Recovery time varies by model and tank size; allow the heater time to reach temperature and the lines to refill — consult your heater manual or a professional for specifics.