Plumbing – Why is the water from the cold water taps warm

Try pulling the cartridge out and turn on the water valve back on. Look to see if you have good flow coming from both hot and cold water holes. Doing this could blow out any debris in the lines restricting flow. Cartridges act weird when water pressure is not balanced between hot and cold.

Try turning off just cold supply and then just hot supply so 100% of water pressure is directed to clear out any debris.

Some showers have built-in valves for hot and cold. Adjust them so same flow is coming out of both holes.

Did you try adjusting the hot water safety limiter? It basicly just stops the handle from turning all the way to hot.

There are a few possible reasons:

• Some hot water recirculation systems use the cold water as a return. In these systems, warm water is returned in the cold water pipe until hot water reaches the the temperature valve that controls the recirculation. Or, perhaps the one-way valve near the pump is failing.

• Hot water pipes could be touching a cold water pipe (probably near the water heater). The two pipes touching would heat up the cold water pipe.

• Cold water pipes could be touching a ventilation duct. In the winter, the duct would be warm and would heat up the cold water.

• No heat trap in the water heater inlet. Hot water might flow up out of the water heater into the cold water pipes.

In the morning, try to feel which parts of the cold water pipe are hot, and that'll be your answer.

Another thing to check, but is likely unrelated, is the condition of a water expansion tank (generally mounted near the water heater) if you have one, or contemplate installing one if you do not (they're needed if you have a pressure reducing valve or a one-way valve in your water meter).