Will air in recirc line cause pump to stop working?

[mangoManFT]

So I tried to save a few bucks and partially drained my water heater to remove the sediment at the bottom. I have a hot water re-circulation pump underneath the water heater connected to a dedicated recirc line. Unfortunately, I did not close the valve between the water heater drain hose bib and the recirc pump when I did the draining, and I believe air got into the recirc pump. The pump is 'on demand' and starts by me clicking a button, and is supposed to shut off when the hot water reaches the pump. It now does not shut off, which is why I believe there is air trapped in it.

Is my suspicion correct - will air in the line cause the pump to not move water anymore?

If so, how can I get the air out? The recirc line runs thru my attic before coming down to the water heater, and as far as I know there is no bleed valve at the high point in the recirc line. It seems I will need to call someone to disconnect the pump and use some sort of vacuum pump to get the air out of the line. There goes the few bucks I saved - lesson learned.

 

[Jadnashua]

There is more than enough pressure in your water supply to purge any air, but maybe not debris. If a bunch of debris got pushed into your pump's line, it may not be actually moving water, and thus, the sensor isn't seeing the temperature rise enough to shut it off.

 

[Sponsor]

 

[LLigetfa]

There is more than enough pressure in your water supply to purge any air

On a recirc loop, the "water supply pressure" is equal on both sides of the pump so it is only the pressure the recirc pump itself can produce that matters. You're and engineer and should know that.

 

[Tuttles Revenge]

Yes.. air can cause your pump to stop pumping.. it can't actually pump air. That is why we install purge valves. There should be a valve that blocks the flow back to the tank and a tee with a purge valve between that and the pump. that forces water from your heater through the entire return loop, through the pump and out the purge.

 

[mangoManFT]

Yes.. air can cause your pump to stop pumping.. it can't actually pump air. That is why we install purge valves. There should be a valve that blocks the flow back to the tank and a tee with a purge valve between that and the pump. that forces water from your heater through the entire return loop, through the pump and out the purge.

There is a valve that I can turn off that will block the pump output from going back in the tank. I'm guessing my failure to close this valve when I drained the tank is the cause of my problem. There does not appear to be any tee with a purge valve, however.

 

[Jadnashua]

Once you turn the water back on, the water pressure will fill the line without the pump running and you open a valve to allow water out and air out. It's a bit different in a closed loop like a hydronic heating system with nominal 15psi and potentially big elevation changes.

 

[Jeff H Young]

I have had circ pumps get air and need bleed out . dont remember if I just opened the hose bib at bottom of tank (circ pump was at bottom of water heater) but I think the valve might need to be between the check valve and pump. I may have lostened a union and just let it leak out for awhile. I usualy have a valve or stops on both sides of pump. its an open system but air can get trapped Im not 100 percent sure of why and cant articulate it that well but I had air bled the air and it fixed it. Someone else can explain why