aquastat problem?

I have a gas-fired boiler, two zone hydronic system with a single circulator. Honeywell triple aquastat L8024E. System appeared to have tankless hot water at one time which is now capped off. The problem is that the circulator started humming with no call for heat from the thermostat. Humming only stopped when power was turned off to the system. When there is a call for heat, the relay closes but water doesn't appear to circulate. When the relay closes I measure 120VAC going to the pump, but with the relay open, I still measure about 40 VAC. Is there a problem with the aquastat?