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Recently the water heater (installed upstairs) had a leak so I disconnected it and removed it. There is a ball valve shut off on the cold line into the tank - I closed it to be able to open the main house shutoff, thinking I could at least use cold water in the house until I had a new water heater.

However, the hot water pipe continued to discharge water, roughly a gallon per hour. I had to open a hot water faucet downstairs for the night so at least it would drain gracefully. The day after I installed a bypass pipe from the cold to the hot water and opened the shutoff - this obviously stopped the leak and allowed me to use the dishwasher and the washing machine, albeit with reduced performance.

In the process to replace the water heater I inspected the plumbing system and I could not really find out why a small amount of water was going from the cold to the hot side. What could be a reason for this? I hope I was able to explain the problem.

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Do you have a single handle faucet?

Most single handle faucets /showers will leak over from cold to hot or from hot to cold during use (if they aren't set at the absolute max/min setting). To prevent this try turning off the local hot water valve at each single handle faucet/shower.

Do you have mixing valve somewhere, like for a bidet system? That would also likely cause a similar problem.

Otherwise it could just be the draining of the remaining water from the hot water pipes at a very slow rate.

  • There is a single handle faucet in the kitchen sink and also the shower/tubs have a single rotating handle. It cannot be the simple draining of hot water because it continued for days at a rate that would not slow down. – Alessio Sangalli Mar 26 at 6:55
  • Seems likely it's your kitchen sink, turning off the local hot water shut off should prevent this. However, I find my under sink stem compression valves leak at least 30% of the time when I need to make an emergency repair, so this may not work unless you have 1/4 turn / ball valves. – virtualxtc Mar 26 at 17:04
  • OK thank you very much. I am in fact about to replace the shutoffs under my kitchen because yes they are stuck and I will install high quality 1/4 turn valves. – Alessio Sangalli Mar 26 at 17:31
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Most often the culprit is the check valves in a shower diverter. But as stated in the other answer any single handle fixtures opened at a mixed temperature will bypass cold to the hot. This includes washing machines filling the tub on the warm setting.

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