Quick Answer:
If both the bathroom sink and kitchen sink produce hot water but the shower stays cold, the water heater is usually not the problem. Confirm the hot supply to the bathroom by checking a nearby sink. If hot is present at the sink, the likely causes are a blocked or mis-set shower mixing valve, a stuck cartridge, or debris in the shower head. Remove and inspect the shower cartridge if you are comfortable doing so; otherwise call a plumber.
Why This Happens
- Shower valves use a cartridge or mixing mechanism to blend hot and cold. If the cartridge is blocked, stiff, or worn, it can stop hot water from reaching the shower outlet while sinks remain fine.
- Built-in anti-scald or temperature limit stops can be mis-set or stuck, preventing hot flow even though hot lines are live.
- Mineral buildup or debris in the shower head or valve can restrict flow of hot water selectively.
- Recent work on the water heater or changes to piping can create air pockets or cross-connections; for those situations see Shower cold after water heater install. For problems only affecting an upstairs unit, see No hot water only upstairs shower.
Step-by-Step What to Do
1. Confirm the hot supply
- Turn on the hot tap at a nearby bathroom sink (or the closest sink). Feel the temperature after a few seconds. This confirms the hot supply to the bathroom plumbing.
- If the sink gets hot, the problem is isolated to the shower valve or shower fittings.
2. Check the shower head and diverter
- Turn the shower on and remove the shower head. Check for mineral deposits or a clogged screen and run water straight from the arm to see if hot arrives at full flow.
- If you have a tub/shower diverter, cycle it several times to clear any debris or misalignment.
3. Locate and shut off the water
- Find the shower supply shutoff if present, or shut off the main water supply before removing cartridge parts.
- Open a nearby faucet to relieve pressure before you start work.
4. Remove and inspect the shower cartridge
- Follow the manufacturer’s steps to remove the handle, trim plate, and cartridge. Take a photo before disassembly so you can reassemble correctly.
- Inspect the cartridge for broken parts, mineral deposits, or stuck seals. Clean with vinegar if lightly scaled; replace if damaged or excessively worn.
- If the cartridge is badly corroded or you’re unsure how to remove it, stop and call a professional.
5. Test and reassemble
- Temporarily re-seat the cartridge and turn the water back on to test for hot flow before fully reassembling the trim.
- If hot water returns, reassemble the trim and test operation to confirm the issue is resolved.
What Not to Do
- Don’t assume the water heater is the problem when sinks are hot—this points to the shower valve instead.
- Don’t force a stuck cartridge or use excessive heat or tools that can damage the valve body.
- Don’t remove parts without shutting off water and relieving pressure first.
- If unsure about valve type or repair steps, a plumber is appropriate; don’t risk causing a leak or permanent damage.
When to Call a Professional
- You have checked nearby sinks and the hot supply is confirmed but the shower still won’t deliver hot water after cleaning and a cartridge inspection.
- The cartridge is seized, heavily corroded, or you can’t identify the valve type.
- There is active leaking, visible damage to the valve or piping, or you are uncomfortable doing the work.
Safety Notes
- Always shut off the water supply before removing valve parts. Open a faucet to relieve pressure.
- Wear gloves and eye protection when working with mineral cleaners or when scraping deposits.
- Avoid electrical tools and keep power sources away from wet areas.
- If you smell gas or see major corrosion on mixed plumbing components, stop and call a licensed plumber.
Common Homeowner Questions
- Why does the sink get hot but not the shower? — The shower valve or cartridge is likely blocking hot flow even though the hot line is live.
- Can I clean the cartridge myself? — Light mineral buildup can often be cleaned, but replace the cartridge if it’s damaged or seized.
- How long does a valve repair take? — A basic cartridge replacement can take 30–90 minutes; more complex repairs or replacing a valve body takes longer and may require a pro.
For more related articles, see the No Hot Water at Shower but Everywhere Else hub.