The plumber connected the cold water pipe to the red colored valve on the boiler and the hot water output pipe to the blue valve. Is this correct? We are having problems with the hotwater. We get a little but then it stopped now it is just lukewarm.
No -- there is a "dip tube" attached to the inlet of the heater so the cold water coming in goes to the bottom and then up the heater as it is heated, with the hot port taking its output from the top of the heater. When the plumber swaps the two, the cold water winds up having to sink down the heater on its own and the hot water is now being drawn from the bottom, which is what causes the lukewarm water you were seeing.
Call a more competent plumber and have them get the tank hooked up correctly.
This is an easy fix that you can do yourself. Switch the connections; I 100% assure you that will fix your issues with not having hot water. The way a water heater works is by letting the cold water (blue inlet) into the tank through a tube in the tank called a dip tube. By doing this the water is heated from the bottom near the burner and the existing hot water it is then taken from the tank through the (red outlet) at the top of the tank.
Hooking it up backwards will give almost no hot water. Turn it off, let it cool, turn off the water, drain the tank, and switch the pipes. Then turn it all back on, and for that matter don't hire that plumber again.