Quick Answer:
If hot water takes a long time to reach the shower after de‑winterizing, the most common causes are partially closed seasonal valves or air trapped in the lines. Start by confirming every winter valve and stop is fully open, then run the hot water long enough to purge air and check for any remaining caps or partially closed stops. If you don’t find an obvious valve or the problem continues, call a plumber.
Why This Happens
When you winterize, you may close isolation valves, install caps on seasonal lines, or drain parts of the system. Reopening those valves can leave pockets of air in the pipes. Air reduces flow and makes the shower sputter or take longer to heat. Pressure changes and any recently fitted equipment (filters, new fixtures) can also change flow rates and make recovery slower—see Shower takes long to heat after pressure change and Long delay after filter install for related situations.
Step-by-Step What to Do
Locate and confirm winter valves are fully open
- Find all seasonal isolation valves you used for winterization (hose bibs, outdoor lines, shower or tub stops, supply shutoffs).
- Turn each valve to its fully open position. Quarter‑turn ball valves should be aligned with the pipe; gate or multi‑turn valves should be fully counterclockwise.
- Verify any caps or plugs you installed on lines are removed.
Run hot water long enough to purge air
- Start with the closest fixture to the water heater and run the hot tap until the flow is steady and the temperature is consistent—this can take several minutes per fixture.
- Move to the shower and run until sputtering stops and the stream is even. If you have multiple fixtures, run them in sequence from closest to farthest to help push air out.
- If the heater cycles or seems to be running but water stays cold, allow a normal recovery period for your water heater (tank heaters need time to reheat; tankless units may need sustained flow).
Check for signs of trapped air or partial closures
- Listen for sputtering, popping, or intermittent flow—that usually means air pockets remain.
- If flow is weak even with valves open, recheck stops and any inline shutoffs (including under sinks or at the shower supply).
- Inspect any seasonal caps, hose bibs, or exterior shutoffs you might have missed.
If noise or hammering occurs
- Brief water hammer when clearing air is fairly common; if loud banging or continuous hammering happens, stop and recheck valve positions.
- Severe or persistent hammering may indicate a different issue (loose pipe straps, faulty arrestors) — consider a pro.
What Not to Do
- Don’t leave winter valves partially closed or caps installed—if you’re unsure what’s open, a plumber is appropriate.
- Don’t try to force valves that are stiff or corroded; you can break a valve. Apply gentle, steady pressure or call a pro.
- Don’t open pressure relief valves, burner compartments, or the water heater tank to chase flow problems—those actions are hazardous and should be handled by a qualified technician.
When to Call a Professional
- No improvement after confirming valves and purging air.
- Visible leaks, structural dripping, or persistent low pressure at multiple fixtures.
- Severe water hammer, loud noises from the heater, or any signs of freezing damage (cracked fittings, split pipes).
- If you can’t find the seasonal shutoffs or are unsure which valves control which lines.
Safety Notes
- Test water temperature with your hand before prolonged exposure to avoid scalding—hot water can reach dangerous temperatures after the heater runs to recover.
- If you must work near the water heater controls or plumbing connections and you are not confident, shut off power to the heater and call a pro rather than attempting repairs you’re not trained for.
- Avoid using excessive force on old valves or fittings; damaged plumbing can cause leaks or flooding.
Common Homeowner Questions
- Why is my shower slow to get hot? Air in the lines or partially closed seasonal valves are the most common causes after winterization.
- How long should I run hot water to clear the air? Give each fixture several minutes; expect 3–10 minutes depending on pipe length and how much air is trapped.
- Could winterization have damaged the water heater? Unlikely if only valves were closed, but freezing that caused cracked pipes or fittings can cause leaks—have a pro inspect if you suspect freeze damage.
For more related articles, see the Shower Takes Too Long to Heat Up hub.