Does this occur because the thermostats are in the wrong place, or is there something wrong with the plumbing? There are two thermostats regulating the flow of heated water once it goes through the boiler. One near the hot water tank in the cealing, and the other near the boiler on the floor being heated. At times the water does not circulate and eventually if the circulation pump does not start the water creates a thermal reverse cycle. This causes cold water to flow into the concrete floor.

Have a professional come out to purge air from the system and confirm that it was installed properly.