We have installed baseboard heaters in our upstairs bedrooms. The problem is the water is flowing and the pipes in the first bedroom heat up but the heat stops as it goes into the second bedroom. We have bled the pipes and it seems we have gotten all the air out. The pipes in the first bedroom are very warm to the touch. How can we get the hot water to flow continually back to the furnace so that it warms up the other two rooms?