I work at a hotel, and every time that I need to turn off the water, when I need to do a repair, the hot water never fully comes back. Some rooms will have it and other rooms won't. I've changed all the mix valves in the showers and still no hot water. Just luke warm. Last time after a couple of weeks it just came back on its own. This is very confusing and time consuming. Please can anybody out there help me. I would be very grateful. F.Y.I the boiler is hot, the pumps are pumping, there is hot water going into pipes, only about a random half of the rooms are getting hot and the rest are getting warm or cold water.

I would look for a problem in the circulation system, maybe a check valve not closing, maybe air in the lines going to the units that are not getting hot water, Also I would check out any type of laundry that is in the hotel. Sometimes the water valve on a washing machine will let cold water go through the water valve back into the hot water line. Water will travel the line of least resistance, so in those cases it might be easier to get water through the washing machine valve that to travel all the distance of the normal hot water pipes... Please let me know what you find. I always like a puzzle.

In addition to letmetellus advice let me ask if you have taken the faucets apart and flushed out the supplies? Let us know, Tom