湯沸かし

1. Origins, structure, and basic meaning

• Structure: 湯沸かし is read as ゆわかし and means “boiling water” and “water heater”.
• Basic usage: It refers both to boiling water before breakfast and to replacing an old water-heating appliance.

2. Common pitfalls and similar expressions

• 湯沸かしを始める / 古い湯沸かしを替える
  • 湯沸かしを始める denotes the activity, whereas 古い湯沸かしを替える denotes the appliance.