Is my thermostat control relay bad? (water boiler)?

I am talking about the type that screws into piping and senses water temp. right outside of boiler in supply piping. My radiator system only gets hot in half the house when I turn (house) thermostat up. My boiler kicks on but only heats up a few radiators.Pump does not seem to kick on. When I byp relay swith and wire direct to circ. pump, it runs and heats up all radiators.Pump then runs constantly but does heat up house. If I adjust house thermastat the system will heat accordingly but with pump running constantly. When I take off the back my relay swith only has one control which is set at 180. why doesn't my pump run when it is wired correctly