I have Navien CC240A unit manufactured in July 2008. It has a Wirsbo (Uponor) 501s thermostat, a White Rodgers Type 8A05A-101 relay and an Armstrong Astro-30B pump. What I want to know is should the relay shut the pump down when the room temperature reaches the thermostat setting? My understanding is that when heat is called for, the thermostat signals the relay which activates the pump. When water begins circulating, this tells the boiler to fire up. The problem is that the pump doesn't stop running when room temperature is reached and eventually the boiler shuts down (I'm guessing that there is an internal limiter) and will not restart unless I shut power off and restart. It will not even deliver domestic hot water when it shuts down; pipe between the boiler and the pump is hot and the pump gets very hot but the pipe between the pump and the manifold (in floor radiant heat system) is cold. I may have a defective relay but would like another opinion. I checked with an installer and he thought it was an airlock but bleeding the system made no difference. He also said that the pump should run all the time but I'm not convinced. Any help that you can give me would be greatly appreciated.