Frozen supply to toilet but not sink

[Hxdai]

Location: Eastern MA

I have been having this kind of issue anytime there's a prolonged time with temperature in the teens or lower. In the second floor bathroom(with exterior wall), I have cold water running for the sink as normal, but the toilet 3 feet away seems to have its supply line frozen shut - no refill after a flush. Took a bit of time after weather warms back up for it to thaw out.

Old foundation, structure was built 2013/14. We bought the house in 2018. Pretty sure it's PEX pipe in the walls.

What could possibly be the cause? And is there any kind of remedy without opening up walls? (besides cracking faucet open, which is wasteful and I'm not sure it even works)

 

[Terry]

The only somewhat safe thing is to add more heat to that room. A space heater perhaps.
Or maybe a hair dryer to warm the wall.

 

[Sponsor]

 

[Reach4]

Toilet supply is probably closer to the outside wall. I don't think running water at the lav is going to help.

You could have a cheap bidet seat set to dribble water in the cleaning mode when things get really cold outside. Or set a timer to remind you to flush that toilet periodically.

Ooh -- ooh.... how about drilling a tiny hole in the flapper to cause the water flow maybe every 15 minutes. Then put an unmodified flapper into place after the cold snap passes.

Long term, enhance the insulation.

 

[Jadnashua]

PEX is quite flexible, and if they didn't use clamps, could easily be pushing tight into the insulation. The long-term solution would be to open the wall, check how the line is run, and make sure that it is on the inside of the insulation. If there are any air leaks, with the typical fiberglass insulation, it can act like an air filter...fiberglass batt insulation only works well if there's no breeze through it...i.e., it's in still air. If you do this on a windy day, while the wall is open, feel for drafts and plug them up with either caulk, or foam sealant.

The good thing, if it is PEX there, is that it rarely would be damaged by the expansion from freezing UNLESS there's a fitting, which, being rigid, might crack. If it were copper or CPVC, you'd have a major problem if it froze.