Hello.

I was experiencing intermittent hot water and noticed that my water circulating pump wasn't working all the time. I thought that was the problem so I replaced it and completed a few other tasks with my hot water system.

1. I replaced the corroded Grundfos water circulating pump and all the piping (including check valve) coming to it and leaving it with copper.
2. I replaced the galvanized pipes that the installer mixed with my copper lines. (The water heater was installed 5 years ago and the galvanic corrosion was extensive in the galvanized lines. The copper areas were not affected)
3. I replaced the dip tube and cleaned out the 40 gallon Rheem Fury water heater. The anode was still is great shape.
4. I flushed the water heater before connecting it to my water system.

The hot water has been working great. I feed two showers, dishwasher, and kitchen sink. On ocassion, however, the water turns warm without there being very much demand on the system. It is puzzling. I don't have pressure balancing valves on the shower valves. Does anyone have any ideas why this is happening? Is it possible that the thermostat is malfunctioning? I thought that the recirculating pump was the issue, but, if the pump failed and stopped working, wouldn't the water heater act like a regular setup with the hot water taking just a little longer to get to each fixture? When the water gets warm, the hot water valve is open all the way with the cold side shut off.

Thanks in advance for your help.

jonathan