hot water circulating pump airlock?

[mjz]

I use a bell & Gossett series 100 hot water circulating pump to maintain hot water at the tap. The pump is set to come on in the morning and run until the thermocouple shuts it off after the pipe gets hot.

The pump is attached and mounted by the hot water tank drain valve. Hot water is circulated through the hot water pipes in a loop back to the hot water tank. The only valves available are the ones to isolate the pump for removal if necessary.

Recently, my hot water circulation no longer works. The pumps runs fine - but the pipe never gets hot. I suspect an airlock somewhere in the loop. My problem is how to flush the loop? I checked the pump (took it apart) and all parts are working (impellar, motor, seal, etc.). I was a bit ##@)_@# when I realized the plumber who designed and installed the system did not put any tap on the loop itself so it can be charged. I'm not sure how it was originally started in the first place to be honest - but it worked for 5 years.

Any suggestions for how to get rid of an airlock in this system? I tried draining the tank's pressure through the drain valve in hopes of dislodging the air pocket - but that didn't work. A friend suggested I bank the pipe with a ball peen hammer (shock wave?), but I hesitate to do that, might create a leak somewhere.

Thanks,

Frustrated in Houston ...

 

[Mr_David]

You need to add a tee and a hose bib some where on the return line, preferably between the pump and the water heater.

Here are some example of how I do it.

I prefer to install a 3/4" threaded ball valve in the drain cock fitting then a brass tee and re-install the drain cock into the tee. Then connect the recirc line to the tee.

he main thing is to have a ball valve between a hose bib and the water heater. Turn off that BV and open the hose bib. that will bleed out any air in the line.
Don't be alarmed if the water comes out looking like tea or coffee.

Some times when I have to bleed a return line that does not have a hose bib I loosen the flange bolts and break the flange gasket seal. toss a towel over it and bleed it into a bucket. Remember to close the valve on line going into the WH.

Another tiop while I am on the subject. Best to mount the pump horizontally and at or below the connection to the WH. This will allow air trapped in pump to migrate into WH easier.

The pump I have mounted vertically will a have I higher tendency to become air locked.

 

[mjz]

Mr. David - see link for picture of my hot water recirculating pump installation:

https://www.dropbox.com/s/v5f0m68gobvnr5t/20161130_132403.jpg?dl=0#

Note the hose bib drain valve is installed closest to the water heater outside the circulating pump isolation valves. To force water to flow through the hot water return loop, I would need to first dismantle the drain valve hose bib and lower shut-off valve and disconnect the bottom part of the bell & gossett series 100 pump in order to "unscrew" everything.

Once removed, I reverse the hose bib with the bottom shut off valve and re-assemble - correct? In this way I can shut off the return flow closest to the water heater and when I open the newly moved hose bib, water from the tank will be forced to go through the loop through the pump and out the hose bib. This should clear any air lock ...

My only concern is that everything unscrews simply and re-threads back to a water tight seal.

Before the problem - water would circulate and get hot by the pump after 5-10 minutes. Now - at best, it gets only warm after 4 hours of running. There is flow, just super slow which I don't understand how that can happen. I thought it would work or not work.

Thanks for your suggestions. I wish I could understand why the original plumber installed the circulation loop this way...how did he bleed the system in the first place at start-up? I would love to do that instead and avoid messing with the pipes.

(and thanks to the admin for getting my posting privileges fixed)

 

[mjz]

As it turns out, the bottom drain was clogged up. There was nothing wrong with the pump, no airlock - no other problem. Once I was able to drain the tank and remove the drain valve, I was able to scrape out the blockage. The tank itself was remarkably clean - not sure how this happened since water flows both ways when the circulating pump is on and off.

Once I was able to get a good flow, the circulating pump put the pipes up to temperature in 10 minutes (vs hours before).

Lesson learned. Thanks all.