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I'm in Dallas where we are experiencing freezing temperatures. The house was built about 25 years ago, i.e. reasonably modern. My water heater (natural gas) is in my open-air attic (edit: and supplied via copper tube). I have just placed a thermometer there to check temps; I believe from feel it is not as cold as outside but it is quite cold and probably freezing temp in that space, but no wind to exacerbate the situation. (edit: yes, temp appears to be ~25°F in attic right now.)

So, the issue...my cold water is running OK everywhere in my house, but my hot water is not at all. The hot water heater fires up when I turn up the thermostat on it, so no issues with its operation. Can I conclude that the feed/pipe from some point inside my house where the line splits off cold feed to the rest of the house and up to the water heater has frozen? If so, should I be overly concerned at this point (it's 8a.m.)? Is there a smart/easy way to locate the point of the blockage if this is the case?

I'll note that if pipe is frozen it's odd because this is the first time in ~20 years this has happened, despite similar freezing conditions in year's past, e.g. the week long freezing-cold snap last year that made the news everywhere for freezing up all the wind turbines here in TX.

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    Type of water pipes? Copper/metal more prone to bursting than plastic types. Being frozen is one possibility, another is a blockage caused by sediment(usually more on hot water side). Need the air temp near the pipes to be below 32 degrees for freezing to happen, the gas heater probably keeps the air just above nearby.
    – crip659
    Dec 23, 2022 at 14:08
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    Warning: Sometimes the first sign that a frozen pipe is starting to thaw is water that starts spraying from a crack caused by expansion of ice, usually in an elbow. You would be well advised to turn off the water supply to the water heater until you are sure that no pipes are cracked. Consider turning off the gas too because if the tank self-drains and the burner starts up, the water heater will be damaged.
    – MTA
    Dec 23, 2022 at 14:29
  • @crip659: Heater is supplied via copper tube. I've added that info to OP. Thanks...
    – AA040371
    Dec 23, 2022 at 14:38
  • @MTA: thanks for the advice! There is a shut-off valve directly at/before water enters heater, but if there is a spot to shut off water between main shut-off (outside at street) and anywhere before the shut-off at water heater, I am not aware of it. Specifically, my house does not have an interior "whole house" water shut off.
    – AA040371
    Dec 23, 2022 at 14:42
  • There's probably a shut-off right after (and right before) the water meter.
    – gnicko
    Dec 23, 2022 at 14:51

2 Answers 2

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Yes, your supply to the water heater is high risk of freezing. I have a similar situation ; all other pipes are in walls or concrete pad so relatively safe from freezing. The lines to and from the heater in the attic are the highest risk of freezing ; they must be insulated. I did it myself and used tape between sections of foam rubber insulation, something the plumber would not bother with. I am near Houston , not as cold as DFW. You may want thermostatic controlled heating wire on pipe in the attic, I did that when I lived in IL. In the mean time be sure to drip hot water during cold spells.

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  • There is some foam tubing on about 2/3 of the accessible (above decking to heater) tubing. I used a heat gun to slowly bring exposed areas up to above freezing temps while I had a hot water tap open. This worked...as evidenced by I was unable top operate the 1/4 turn cutoff there before, and then was able to afterward. Yes, I did then wrap in a thermostatic controlled heating cable (EasyHeat product from Lowes Depot)...I hope it is generally safe! Will probably come back and wrap all exposed tubing with better insulation later today...wish I had done that when I put in heater :--/
    – AA040371
    Dec 23, 2022 at 17:06
  • I do have cold faucets on drip at times like this, but never thought to need the hot water dripping as well. My understanding is a water drip does not prevent freezing, but only serves to allow air pressure build-up to escape instead of busting out seals and joints when pipes actually do freeze-up.
    – AA040371
    Dec 23, 2022 at 17:07
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It's likely frozen just before or just after the water heater in a location that's between the warm part of the house and the warm zone immediately surrounding the heater.

At this point, your next move is likely to head up to the attic and inspect the pipes. Look for cracks or splits especially near elbows.

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  • I suspect you are right! It really is the only place the supply is exposed to frigid temps, although I can't explain why this is first time it has occurred over all these years. I'll search online to see if there is a generally accepted/safe way to keep that part of pipe warm, e.g. electric space heater or thermal heat wrap or something.
    – AA040371
    Dec 23, 2022 at 14:43
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    Heat tape will work. Sometimes just packing some insulation around the pipes is sufficient. Allowing the section of pipe to have more contact with heated air works in some situations, too. It depends on the situation. When you find the frozen section, post another question with pictures, etc. asking how to prevent it from freezing.
    – gnicko
    Dec 23, 2022 at 14:58

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