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[helmick1]

Had my first issue with my OWB a couple days ago. We had a momentary power outage on Sunday evening, maybe a couple seconds. I went out to fill the stove about an hour later and the thermostat on the boiler was at 203 and the pump was not running, this was about 8pm. I took the pump off and couldn't see anything stuck in it and it spun by hand. I plugged it in at the garage and it ran, so I went back out and put it back on the stove. by then the temp at the stat went down to about 160, as soon as I put the pump back on and opened the valves the temp immediately started going up to over 190. The hot supply line leaving the stove was very hot to the touch, but the return line was not hot at all. The pump was running, but making a whirring noise. I went inside and cranked up the stats in the house to try to help move the heat, but the air was cold. I crawled under the house where the heat exchanger is and the supply and return lines were not hot at all. So then I figured I had an airlock so I hooked a hose to the stove drain and closed the valves and unhooked the lower line at the circulator pump and backfed water through the lines. Seemed liked there was some air that came out, but didn't seem like a lot. I hooked the pump back up and opened the valves and tried again and still had the same problem pump running but not pushing hot water and the stove temp started spiking again. So, I went through the whole airlock process again, same results. By this time it was 1am and I was stumped so I shut the power breaker to the stove and went to bed. The next morning I took the pump off again and everything seemed fine. I put the pump back on and opened the valves and again the temp started spiking, I left the valve to the pump open and closed the return valve and the pump stopped making the whirring noise and I opened the return valve again and it started whirring again. I done this four or five times and could hear air moving through the lines, so I opened the fill valve at the front of the stove and run about 5 gallons of water trough it and some air came out. Went to the back and the temp started dropping and the lines started getting hot. Running perfect now (so far). I'm stumped, any thoughts? Stuck pump? I get the problem with the air in the lines, but what could have caused the pump to stop working in the first place? Also, about the air in the line could it be that it was the pump getting primed that was making the whirring noise? Hopefully it was just a freak thing and doesn't happen again. Sorry for the long post, but just trying to see if anyone else has had this happen or any thoughts about it.

[Sprinter]

Hard to say, is your boiler higher or lower than the HE? Or same? 

So adding water from the fill helped solve the issue, if I understood your post right? It does take quite a bit of air to lock a loop and the circ has to be about at its max head for it to not push it thru. Like a good 5'-8' section of pipe with all air.

It's always a good idea to have boiler drains or a purge valve on the downstream side of the problem area. Now that you know how to fix this.  Now what was the cause? Little more detail about that loop.

[RSI]

Is the pump at the boiler or in the house?

[helmick1]

The pump is on the stove outside, about 100' away form the heat exchanger. The stove sits a couple feet higher than the exchanger. I'm not sure if adding water at the fill valve is what fixed the issue, or if it was the combination of opening and closing the valves and adding water. It was maybe 5 gallons low from me working on it. The pump is a Honeywell 3 speed that is set on the highest speed.

[Wood Nutt]

I had a situation similar when I fired up for the first time on initial fill of my shop loop.  In my case, the HX is several feet higher than the boiler and the pump is on the back of the boiler .  I assumed the pump would prime itself, but finally figured out that I had a small air bubble inside my pump and the pump was cavitating I think becase I had a column of water downstream of the pump several feet high.  I blead the air out of the pump itself (cap screw on the end of the pump motor) and it took off pumping and has been running fine since, once I got that air bubble out.  Your case could be that the little bit of extra weight of the water you added upstream was enough to push the air on thru the pump?  That is one theory you can think about.  Glad it is working now though.

[Sprinter]

If the boiler water level is higher than the rest of the loop, then it should bleed itself easily unless there is a spring check. A swing check would not stop it from bleeding. 5 gallons is a lot , especially when 100' of pex holds 3.03 gallons of water. If you don't have ball valve flanges on your pump then I could see draining the whole line , if there is a high spot.