Quick Answer:
If your shower takes longer to reach hot when the washing machine is filling, the washer is likely competing for hot water or pressure. To check, run the shower alone and time how long it takes to get hot, then run the shower while the washer is filling. If the delay only happens with the washer running, the problem is shared demand or reduced hot flow at startup.
Why This Happens
Most homes have limited hot-water flow and a single supply line feeding several appliances. When the washer opens its fill valve, it can draw significant water volume. That reduces the hot-water flow to the shower or changes the cold/hot balance in the shower valve, so hot water arrives slower or the shower temperature dips.
If the behavior started after recent plumbing changes, look for installation issues such as valve settings or swapped lines — this is a common clue of altered plumbing work like rerouted lines or a replaced mixing valve. If you noticed a change after work, pay attention to **Delay started after plumbing work** as a sign to mention to a plumber.
Step-by-Step What to Do
Step 1 — Establish a baseline
- Run the shower with no other appliances using water. Note how many seconds it takes to feel steady hot water and whether the flow rate is normal.
Step 2 — Repeat the test with the washer filling
- Start the washer on a normal fill cycle so it draws water, then run the shower the same way. Time how long it takes to reach steady hot.
- Compare results. If the delay is noticeably worse only when the washer fills, this points to demand/flow competition rather than a problem with the shower hardware itself.
Step 3 — Check washer settings and behavior
- Verify whether the washer is set to use hot, warm, or cold for the fill. If it uses hot or warm, it will draw hot water and affect the shower.
- Try a cycle that uses cold fill only (if available) to see if the shower delay improves.
Step 4 — Look for other clues
- Test other hot-water fixtures while the washer fills. If multiple fixtures are affected, the issue is system-wide flow or water heater recovery.
- Note whether the delay gradually worsens over time or only happens at startup; persistent worsening can indicate scale build-up or a failing valve affecting flow. If this happens, consider that **Shower hot water delay worsens over time** may point to sediment or valve wear.
Step 5 — Simple fixes to try
- Stagger use: run showers and washer at different times when possible.
- Set the washer to cold fill for cycles that don’t need hot water.
- Check and replace low-flow or clogged shower aerators and showerheads if flow seems restricted.
What Not to Do
- Don’t run the washer and shower together repeatedly just to test the issue—doing many quick tests can be uncomfortable and raises the risk of scalding or slips from changing water temperatures.
- Don’t raise the water heater temperature beyond recommended safe limits to “force” hotter water; that increases scald risk.
- Don’t attempt invasive repairs on your water heater or plumbing if you’re not experienced; if demand causes issues or you suspect internal problems, a licensed plumber is the appropriate contact.
When to Call a Professional
- Persistent delay even when only the shower is running — could be a shower valve, blockage, or hot-water delivery problem.
- If multiple fixtures lose hot water or flow while one appliance runs — this may mean undersized supply lines, faulty valves, or water heater recovery issues that need a plumber to diagnose and fix.
- After recent plumbing work that coincides with the change in performance — mention that the issue began after work so the plumber can check routing and valve connections.
- Visible leaks, strange noises from the water heater, or if you smell gas — stop tests and call a professional immediately.
Safety Notes
- Avoid repeated quick tests that expose you to sudden temperature changes; this can cause scalding or falls in a wet shower.
- Keep water heater temperature at or below 120°F (49°C) to reduce scald risk unless advised otherwise by a professional.
- If you suspect gas leaks or electrical faults with the water heater, stop using appliances and call a qualified technician right away.
Common Homeowner Questions
- Q: Why does my shower cool down when the washer starts?
A: The washer draws hot (or mixed) water and reduces the available hot flow, changing the shower’s temperature balance until hot supply stabilizes. - Q: Can I just run both at the same time?
A: You can, but expect longer warm-up times; staggering cycles or using cold-fill washer settings reduces the problem. - Q: Will switching the washer to cold fill fix it?
A: Often yes—if the washer is the main hot-water draw, using cold fill prevents it from pulling hot water from the tank while you shower.
For more related articles, see the Shower Takes Too Long to Heat Up hub.