Recirculating Pump Not Turning On

So I’ve got a grundfos pump (up 26-64 f) used for pumping the boiler water to my hydronic floor heat. It always worked fine but has suddenly appeared to stop turning on when there is a call for heat. This AM I believe it did turn on briefly but now I’m unable to get it on again. Heat call is happening as the boiler is turning on. The pump is pretty warm to the touch but I don’t know know it it’s warmer than normal.

Anyone known if there are common problems to check on these guys? It’s a pain in the butt to reach as it’s at the back of the boiler closet of course.

thanks!!

 

Hi, do you have a meter? I would follow the cable from the pump to the control and find the 2 conductors there and test for 120 VAC on those terminals.
post some pics of the control so we can assist.
Geo🇺🇸

 

Another common issue ( ok common in my house ) was air getting into the system and air locking my circulator. Might be work trying to purge the air.

 

Well good news and bad news. Good news is that when I use the second thermostat that controls a different zone, the pump spins up and works. Bad news is that the other thermostat, despite calling for heat, still doesn’t spin the pump up. Is it possible the downstream valve from the pump that allows the water to flow down that leg can prevent the pump from spinning if the valve isn’t actuating or has failed?

 

And now I can get the pump to run with the second thermostat as well. I’m wondering if there is some sort of thermal cut off or something? Intermittent problems are a pain.

 

Hi, if the pump runs on zone 2 it’s probably not a pump problem, do you have zone valves? does the OTHER zone fire the boiler?
post some pics.
Geo🇺🇸

 

I think the question i have on this is in the zone that is not working does the water circulate if you manually open the zone valve? I wonder if the thermostat is the issue, if there is one 1 circulator pump it would sort of be a all or nothing scenario of if its able to push water around. Something to try would be to turn up the temp on the zone you know works to get the burner running and manually open the valve for the zone that is not working. If the zone that is not working as expected heats up this eliminates the circulator pump as an issue and leaves the zone valve and potentially the thermostat as problems. The thermostat can be ruled out possibly by swapping in a known working one especially if both thermostats are the same. Some systems you can also short the correct wires to rule it out, but thats heavily dependant on the system. My system is a very old system with just 2 wires to the thermostats ( well until i recently upgraded and added a transformer so i have constant 24v to the smart thermostats )