Water is coming out warm from cold faucets

[Shane Wood]

Two weeks ago, I replaced my vented gas water heater with a power vent gas water heater, due to venting issues. Since that time I've noticed in all of my faucets and showers, when I turn the cold water on, it's cold to start but then warms up (82 degrees). I've had a plumber in who checked all the faucets (shutting them off one at a time), w/d, etc., he came to the conclusion it had to be a bad cartridge in one of the showers, so I replaced the upstairs shower cartridge and it didn't fix the issue, so I then replaced the downstairs shower cartridge and am still having the same issue. I do have a single handle faucet in the kitchen and downstairs bathroom sink but they've both been shut off and we tested the other faucets but still had the issue which I'd think should rule that out, right? I'm definitely not a plumber and just need advice and where to turn to next, could it be something to do with the water heater? Also, it is not a recirculating system and does not have an expansion tank. Thanks in advance!

 

[Reach4]

First, do you have one of these?

If so, close the valves feeding it.

Close the valve feeding the WH. Run cold water. Do you still get warm water? If so, the water is warmed by something other than mixing with hot.

If that is not it, turn on the supply to the WH, and run cold somewhere. Feel which pipes, hot and cold, to all of your suspect valves are warmest. An IR thermometer would be handy if you have one, but your hand may be sensitive enough.

 

[Sponsor]

 

[LLigetfa]

Is this city or well water? I've seen where a failed check valve would cause the water to run back and forth heating it in the process. Also saw where a leak in the well would recirculate the water until it got hot.

Had another case where the neutral on the mains supply was open and the protection ground was carried by the water line heating the water in the pipe.

 

[WorthFlorida]

Does the new WH have heat traps installed?

Similar to Reach's suggestions, close all hot water shut offs at all fixtures and then run the cold water at the furthest fixture from the water heater. When it is cold, start opening one HW stop valve at a time by starting at the second farthest fixture. Keep going and when the water gets warm, the last stop valve opened is the source of the trouble.