hot water runs cold after 5 min. Help please!
We have a mystery on our hands so the following is details of our situation. We are having an issue with the hot water in our building. After about five minutes using the shower or any faucet, the hot water turns lukewarm and then cold. At first we thought it was the water heater as the culprit, but it seems to be more complicated than that. I have the best plumbers in San Francisco, but we are all baffled as to what is causing the problem.
The unit is a two bedroom two bath, 1200 ft.� apartment with a high-efficiency State 50 gallon water heater, powering the hot water. During normal use, there should be more than enough hot water for a long shower. In fact, everything worked fine up until recently. The water heater seems to be running fine. The pilot is lit correctly, and it turns on when it needs to. In fact, we recently installed a temperature gauge to measure the water temperature. When the water is off it reads 130�, but when turned on the water goes down to about 100�. In troubleshooting the problem, my plumbers thought it may be a check valve that has gone bad or the thermostatic valve to regulate the water temperature that is attached to the system.
The plumbers replaced the check valve and the thermostatic valve, but the same problem exists. After about five minutes the water temperature will go down to about 100� or less. There is a recirculating pump attached to the system that is also working correctly. The plumbers don't think that has anything to do with the problem since the pump should not affect the water temperature. At any rate, my plumbers believe that there is cold water somehow getting into the system. The water that comes back into the return comes back cooler than it goes out.
In addition to all of this, we have an automatic washing machine shutoff valve installed in the laundry room. My plumbers now suspect that this is actually the culprit. Somehow this unit has gone bad as is allowing cold water back into the system. You can see details of the Watts unit we have installed here:
To make things more complicated, the 50 gallon water heater also powers a radiant heat floor system to heat the house. This is a closed looped system and should not necessarily affect the water temperature of the fixtures.
Here is where the mystery becomes more interesting. The building is a two unit building, and each unit has a separate but identical plumbing system each using a 50 gallon state water heater. I recently realized that we are having the same issue in both units! Is it possible that in both units the automatic washing machine shut off is causing the problem? Or is there something else causing this issue? If anyone has any ideas or experience with something similar we would love your help on this. If anything, this could serve to help someone in the future with the same problem. Thanks!
Here is a link that might be useful: http://www.watts.com/pages/learnAbout/intelliflow.asp