I have an oil burning furnace that heats the house and hot water. I have 60 gallon hot water tank located right next to the furnace. Both furnace and tank are located in the middle of the basement away from any walls. Lately I am only getting barely warm water in the morning and as the day progresses water goes completely cold and the cycle continues every morning. There is a thermostat attached to the water tank that was set to 120. I moved the dial to 140 but no change. There are three zone valves. One for 1st floor heat, one for 2nd floor heat and one for the hot water. The insulated pipe that comes from the zone valve to the water tank is hot near the valve but barely warm near the tank.
My guess is either the zone valve or the thermostat in the hot water tank is not working.
Any help on how to properly diagnose/fix this issue is appreciated.
*Update: right now all cold water, all the time.