I get hot water in the cold taps and toilets on one side of the house. It does turn cold after getting very hot in all but one toilet which always seems to be hot. We have done minor renovations that involved only turning the main water off but nothing on the pipes.

Are hot and cold pipes touching each other, especially a long run? Exposed to the Sun?

Neither. And we have lived in this house for 15 years and never had this problem until a year ago. I wonder if, in turning the main water off and on during renos, I might have created some kind of vacuum that is reversing the flow temporarily. I don't know enough about water pressure to figure out how that might work.

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Originally Posted by Judy B50

Neither. And we have lived in this house for 15 years and never had this problem until a year ago. I wonder if, in turning the main water off and on during renos, I might have created some kind of vacuum that is reversing the flow temporarily. I don't know enough about water pressure to figure out how that might work.

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A more likely culprit would be a worn cartridge in a shower or bathtub mixing valve that is allowing hot water to pass through and into the cold port.

Also -- Do you have a hot water recirculating system?

If so, it's possible that a check valve isn't seated properly and is allowing the pump to flow into the cold system.

I tested the shower cartridge theory by turning on the shower to full cold and then running the other taps. That seemed to work. I removed the cartridge and it doesn't even look like the correct one so I am going to the plumbing store today. Will let you know tomorrow.