I hope this has been resolved, but if not, here are a couple of ideas for you.
First, was it the cold water hose that was replaced? If so, did they turn the valve back on? It should be in the full open position, so this is the first place to look. If this isn't the cause, check your hot water heaters setting. If you have it set as high, or close to as high as it will go, turn it down. There are many problems associated with the temperature being set to high, including reducing the life of the water heater and personal injury. The other idea that would fit this problem is, have you checked your mix-it valve? Easiest test to do is check the water in your toilet's water tank. If it's warm or hot, you may wish to consider changing the mix-valve, or valves depending on your home.