So my problem is that my shower and lavatory is only lukewarm. However, the water at my kitchen sink is very hot. My shower and lav valves are old syle two handle. My kitchen sink faucet is of Moen design. At first I thought that my cartridge at kitchen sink was backflowing and mixing cold water back to the shower, so I replaced it because I could feel water surging through it when the shower was on. That didn't solve the problem. My plumbing layout is as follows: h20 heater to kitchen sink, then to shower, then to lav. If you need more info please ask. Thank you.

I forgot to add the water heater serves the washing machine prior to other fixtures, and it is hot, as well.

Kalin... try shutting off the water to the washing machine (shut valves off)... could be that the mixing valve at the solonoid valve has gone bad... ;)

Let me know what happens, OK?

Mark