hi y'all!
I'm hoping someone out there can help me. I have a simple 1-zone ,4-loop system, staple-up covering about 800sq. ft..  Hot water is from a 70 gal. domestic hwt.located  15' away. The circulation pump seems okay [humming away]
but the pump isn't drawing water past the heat-control valve even on manual [open]. I've checked each loop for flow & there doesn't seem to be any  oxygen or other obstruction. System's been working fine for the last 7 years but i'm at a loss! I live way outin the boonies & it's a problem getting anyone knowledgeable out to my place on these roads in Winter ...to say nothing of the cost! Fortunately, we have a gas- fireplace to tide us over-- but it ain't cheap to operate! The mechanics of the system are all Taco & consist of pump, heat-control valve, little air do-hickey at the top , ball -valves with  thermo- stat upstairs connected to heat c. valve. Any help greatly appreciated.