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I'm changing the gas valve in my hot water heater. Exactly as shown in this video.

The video is queued at the point where they drain the water from the hot water tank. My question is... why?

Note: The instructions from the manufacturer also call for draining the water from the tank first too. So the video makers aren't just making up this step for nothing, I presume.

Why does the hot water tank need to be drained of water in order to replace the GAS valve? And what bad things could happen if I replace the gas valve without draining the water out of the tank?

Fig.1. Video maker points to hose connection point for draining tank

enter image description here

Edit: According to this video, it looks draining the water might be a safety precaution? As any hot water left in the tank could be a scalding risk? So it seems like if I'm certain the water in the tank is cold, I can skip draining the tank?

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    The valve should have a part that inserts into the tank to measure temperature in the tank and decide when to turn on and off. When you remove that part, the water will drain out anyway. Better to control the drain especially if the water is hot. – ArchonOSX Jan 17 '18 at 11:19
  • Answers go down there @ArchonOSX :) – mmathis Jan 17 '18 at 14:21
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The valve should have a part that inserts into the tank to measure temperature in the tank and decide when to turn on and off. When you remove that part, the water will drain out anyway. Better to control the drain especially if the water is hot.

  • there is no should in the temperature probe inserting directly into the tank. Nothing like 50-gal of unwanted water on the floor. – Paul Logan Jan 17 '18 at 16:55
  • You saved me a mess! You too @PaulLogan. 🙏 – Mowzer Jan 17 '18 at 18:22
  • I put should because I believe most are that way. However, it is possible some models could have a thermowell and the temperature probe would be isolated from the water. – ArchonOSX Jan 17 '18 at 18:25

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