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A few days ago, the bathrooms on the 2nd and 3rd floor of my townhouse stopped getting any hot water. Nothing comes out of the faucets when they are turned all the way to the hot side. The cold water works fine. The kitchen on the main floor and bathroom in the basement still receive hot and cold water.

On the day this happened, we checked our smart thermostat and it shows that the basement was under 10 degrees Celsius, and main floor was around 14 degrees. The weather outside in Toronto was around high -10s and low -20s. We suspect this has caused a section of the hot water pipe to freeze and have been keeping all areas of the house around 23 degrees for 3-4 days now, but a couple things don't seem to make sense if this suspicious is true:

  1. How does/did the hot water pipe freeze before the cold water pipe?
  2. How has running heaters near the walls and increasing internal temperatures not melted or thawed the problem sections yet?
  3. We have been keeping a couple of the faucets on the 2nd and 3rd floors slightly open to relieve any pressure buildup. With only the hot water tap turned on, sometimes nothing comes out and at other times, a slow stream of cold water comes out.

Townhouse was built in 2012. Water boiler/heater is in garage. Heating works fine. Water pressure in working areas (basement and main floor) seem fine. I have no idea what is going on. The weather is not going to warm up anytime soon and I want to prevent any further damage or complications.

Photos of faucets: https://i.sstatic.net/bQ5eb.jpg

Any suggestions/advice/tips are welcome! Thanks!

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  • Houses in cold climates are probably built different to what I'm used to, so maybe this is a dumb question, but are you sure there isn't a secondary water heater that supplies the upper floors? I've seen secondary water heaters in the attic, for example.
    – JPhi1618
    Commented Jan 3, 2018 at 22:09
  • @JPhi1618 I am fairly certain we only have a single water heater. Our attic is empty as well!
    – VeiN
    Commented Jan 3, 2018 at 22:48
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    One example: I happen to know the pipes to my kitchen sink are in two different joist spaces in a finished basement ceiling. We had the deck off the first winter (it was unsafe and didn't get rebuilt before winter) and there was one single 3/4" hole that could allow cold air to enter. That cold air froze the hot, but not the cold water. Also hot water doesn't stay hot in the pipe, it cools unless there is a loop for keeping it always hot.
    – Tyson
    Commented Jan 3, 2018 at 22:57
  • @Tyson thanks! that's insightful. Without knowing ahead of time, do you have any suggestions on actually finding where the pipes are in the wall asides from best guess trial and error?
    – VeiN
    Commented Jan 3, 2018 at 23:10

3 Answers 3

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1) How does/did the hot water pipe freeze before the cold water pipe?

  • Once tap water has been heated, most of the entrapped gases such as chlorine, fluorine and air are released losing the insulating properties that cold, treated water would have.

2) How has running heaters near the walls and increasing internal temperatures not melted or thawed the problem sections yet?

  • The walls provide greater insulation/resistance than you suspect. You don’t have enough heat and/or haven’t given it enough time.

3) We have been keeping a couple of the faucets on the 2nd and 3rd floors slightly open to relieve any pressure buildup. With only the hot water tap turned on, sometimes nothing comes out and at other times, a slow stream of cold water comes out.

  • Whatever marginal melting occurs in the hot water pipes, occurs in a very thin layer with direct contact with the pipe wall. The pipe core remains frozen, which chills the small amount of water flowing around it.

Movement of the melt water is the key to re-establishing flow. Pipe thawing of this type is usually done by passing electric current through the metal pipe. Welding contractors are best suited for the job.

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  • Thanks so much for the insight! In one of the wall access points, we managed to locate the cold and hot water pipes. It looks like they are plastic/pvc to me, but I am not 100% sure. Can you tell? Picture: imgur.com/a/3IXHb
    – VeiN
    Commented Jan 4, 2018 at 14:47
  • My main problem now is preventing this from occuring again, ie. trying to find and fix the root cause. I bought some insulation and stuffed it in walls near the water main access door and another in between my basement and first floor. I also got an infrared camera to detect temperature differences but it is quite hard to tell through the drywall and I don't want to have to cut holes everywhere if possible. Any other solutions on preventing pipes from freezing?
    – VeiN
    Commented Jan 4, 2018 at 14:52
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We brought in a couple heaters and set them to 26 degrees Celsius. We also kept faucets dripping "hot" (actually just cold) water. We additionally opened the water main access door and blew hot air into the walls, as well as heating up all our bathrooms with the vent fans on. This all happened for over 72 hours. A few hours ago, our hot water has been restored.

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  • Thanks for the update. Hopefully you can try to narrow it down a little for the future, but for now, just letting faucets drip might be enough to prevent it.
    – JPhi1618
    Commented Jan 4, 2018 at 16:47
  • @JPhi1618 thanks! I will do my best to figure out where the problem areas might be, but I don't have any real experience :)
    – VeiN
    Commented Jan 4, 2018 at 16:50
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You have plastic pipes, so I'm afraid that rules out the electric thawing technique. Heat tapes/cables might work if you have an isolated frozen section. The better variety are thermostatically controlled. Make sure you find one approved for plastic pipe.

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