My tankless water heater (Stiebel Eltron, about 5 years old) has been making this weird humming and crackling noise when it heats up for a few weeks now. It never did that before. Water comes out normally and the temperature is right, but the noise is really getting to me. Can that still be safe or should I call a plumber?
Is the humming more of a deep vibration or more of a high-pitched whistling? With tankless water heaters, noises like that often come from limescale buildup in the pipes or the heating element starting to vibrate - pretty normal for older units, but not something to ignore. If the temperature is stable and the water flows normally, there's no immediate safety risk, but I'd still have a plumber come take a look before it gets worse. Sometimes a descaling does the trick, sometimes a part needs to be replaced - someone on-site can tell you pretty quickly.
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