Loud pounding sound whether circulator started pumping

novice777

Hi,
I have a gas boiler heating both floors of my house. The configuration is such that both floor return pipes combine and go thru the single circulator and then into the boiler. Earlier this year the boiler failed to circulate the 1st floor system. The repair guys first thought it was the control valve failure, but later found it was working, Another guy said it was electrical failure and replaced the thermostat. System seemed to work after the replacement, but it failed again overnight with the same symptom (1st floor not circulating). Later it was diagnosed as an ailing circulator and it was replaced. So it was the ailing pump issue right from the beginning, though I am not sure why the ailing pump was able to circulate 2nd floor, but not 1st floor. This system has been generating a lot of metallic air noise all along and I could hear the water flowing in the pipe all the times. I did flush the whole system in the past and also before I turned on the boiler this month and I could see air bubbles came out. Unfortunately now there is a bigger problem. The system generated a very loud pounding sound I believe whenever the circulator first started to circulate water on either floor. The sound was loud, like the pipe pounding heavily on something, or sometimes the radiator rattled violently. It is very annoying and worrisome. The air vent has been broken (leaking) in the past so I closed it completely. I tried to bleed upstair radiators, but in one radiator I only saw a couple drops of water and then no more water coming out, nor air that I could detect. There are 3 heating loops on the 2nd floor and I think I have heard the pounding sound generated on any of them. In other words, the sound could happen at a couple different locations, I believe. It looks like whenever the pump circulates it generated some sort of momentum energy and rattled the pipes heavily (air?). How should I go about fixing this problem? Thanks in advance.

Zman

Could you post pictures?

mattmia2

Is the water feeder working? What does the pressure gauge say? Unless a valve is closed somewhere the pressure from the pressure reducing valve should pus water or air out when you open a bleeder valve if the prv is functioning and set to the correct pressure.

novice777

The water feeding valve appears to be working. I flushed the water by slowing draining water into bucket (the drain is located after the pump but there is no shutoff before going into the boiler, so I guess water flowed in parallel?) and water pressure is around 12~13 psi. After water heat up, it increased a few psi to 16 psi or so. The water reducing valve pus air out? I don't get it. I thought it was the air vent that let extra air out.
Hi Zman, pictures will be posted.

Jamie Hall

If you open a bleeder on the second floor and there is air in that radiator it should come out -- and then water should come out quite vigorously. If it doesn't, either the bleeder isn't really open -- or you have nowhere near enough pressure in the system -- or you have some closed valves.

Your description isn't completely clear as to whether you have one zone -- first and second floors combined -- of two, with separate thermostats and zone valves for each floor. It makes a difference. I think I see two zone valves...

I think I would go back to square one. Make sure that the automatic feeder is able to feed (all the valves open). Now call for heat -- in either zone, if there are two. Go to the calling zone, and open the bleeders, one at a time, on all the radiators in the zone. All of them should release air, perhaps, but should also, once the air is gone, release a solid stream of water. Do both zones. Check the system pressure from time to time if you are getting water out; the automatic feeder should be holding the pressure at 12 to 15 psi.

Now the boiler has been running for a bit, so you should be able to feel hot water in the pipes going away from the boiler. If not, that zone is not able to circulate. Which isn't a pump problem -- the pump is common to both -- but, if there are zone valves, is most likely the zone valve not opening properly.

Hearing rushing water in the pipes suggests strongly that there is a lot of air in there. Opening bleeders won't get rid of all of that, and you may have to purge the system.

The banging? Could be cavitation or loss of flow (air) at the pump.

Zman

The way yours is set up, you are pumping into the expansion tank which tends to cause air issues.
I also wonder if the new circulator has a check valve installed. That would explain the banging noise. Can you post a picture of the right side of your circ?

novice777

There are 2 flow control valves. The house is 50~60 yrs old and the air bleeding vent are not working that well. Oh, I forgot to mention that the first floor heating is under the slab and the associated air bleed vents are old and rusted and I wouldn't dare to force them open. What I tried were the 2nd floor radiators bleed valves. Even the ones on 2nd floor are either hard to access, really old and worn. I am not sure whether the lack of either water nor air came out is really that or it was clogged.
When I flushed the system (to get rid of metallic noise) I didn't touch the pressure feeder's lever and just slowly drain the water out to bucket. I saw air bubbles. I can feel that hot water is flowing in each loop (1st and 2nd floors), though I cannot be sure they are equally as hot. I will pay some attention to that, may be that will give some insight. So the banging sound happened at different location at times. Last night, it seemed concentrated on my master bedroom radiator and I could hear it all night Probably my neighbors could hear it too. Purge the system? I already flushed it earlier this month. Earlier this year (before this banging sound happened) when I flushed the system, metallic sound (not the banging sound which is way louder) was reduced for a few days then came back.
@Zman, pumping into the expansion tank? I thought it is pumping into the boiler? More pictures are posted.

Jamie Hall

It is pumping into the boiler... but the expansion tank is on the other side of the boiler, so effectively it's pumping into the tank through the boiler. Not the best situation, but livable with if everything else is working as it should be.

Draining and flushing is not the same as purging. In purging one gets a really high flow through the system which will sweep the air out; in flushing that doesn't happen necessarily.

novice777

@Jamie, if there is a good chance that purging will fix the banging sound permanently I will be happy to do that. However, I am still not certain that after purging, the air won't come back soon. So I want to figure out what happened. May be the repair guy introduced some air into the system when he replaced the circulator? When I flushed the system last year for the first time, I did lift the pressure feeder to force quicker water flow as I thought that the boiler tank was draining in parallel would need more flow.

Paul Pollets

This system has several piping errors...the existing return tee is bullheaded to the pump and the the supply is pumping towards the expansion tank, rather then away from the tank. Isolation valves and drains on all circuits would assist purging. Try reading Dan's book...https://heatinghelp.com/store/detail/pumping-away-and-other-really-cool-piping-options-for-hydronic-systems

Zman

Your new circ has a check valve, that is what the "IFC" stands for.
When the zone valves close, the heat loop is sealed and can no longer "see" the expansion tank. The noise you are hearing is the pressure equalizing when the zone valve opens (the little bit of air trapped is making it worse). If you remove the circ and take out the little white plastic check valve your noise should go away.https://www.youtube.com/watch?v=nEC15uplGxY

novice777

@Paul, don't think I am going to change the configuration of the boiler. Are you saying that I most likely need to purge the system in order to get rid of all those air and the banging sound?
@Zman, not really understand what you are saying (I am no expert on check valve). However, that means I have to get another repair guy to remove the pump. Hopefully this one will be more reliable and less expensive, as I spent $1100+ on the last one. I think I will wait till this cold wave is over to get another technician after the weekend.

mattmia2

If the tech that swapped the pump swapped a pump without a check valve for a pump with a check valve they should come back out and remove the check vale for free unless they had a very specific reason for adding it (but since you have zone valves I don't see a reason to have a check valve)

novice777

@mattmia2, I don't think those guys will do it for free. I had to threaten stop check payment (of $1100) before they agreed to replace the pump for free, as the problem (of not circulating the 1st floor) obviously didn't go away after the control flow valve replacement (only the upper control portion, not the bottom portion) and the thermostat replacement.

mattmia2

You might want to make sure that radiant loop isn't leaking. Turn off the feeder and let it sit a while and see if it holds pressure.

Removing the check isn't difficult, you just need to remove the 4 bolts and pull it out with a wire hook or some needle nose pliers, then put it back together, make sure the gaskets go back in to the grooves in the flanges as you reassemble it. You will need to either drain some of it or shut off isolation valves if there are some. Have a bucket and let the water out slowly.

novice777

@mattmia2, thanks for the suggestion on checking leak. That has always been one of my concerns. I will do that when temperature is above freezing after the weekend.

Zman

The check valve removal is pretty simple. You would need to close 2 ball valves and drain and refill the top portion of the boiler. The removal and replacement just requires basic mechanical skills. The gasket needs to be straight and everything needs to be tightened evenly. You just need to make the reveal between the flanges even.

novice777

I want to thank you all for all the useful suggestions. I have some business to take care of over the weekend and will wait until after the weekend when the temperature is warmer to try your suggestions. Will update the progress later. Thanks again.

novice777

Yesterday the temperature got warmer so I started. The circulator was a bit more difficult to remove due to the bottom rubber gasket which was strongly bonded (I could even lift the corner of the boiler when I lifted the pump!). Finally decided to get new gaskets from HD and pried open the gasket. Yes, there was a check valve and I removed it. I also wanted to replace the air vent, but it was too tight and I don't have a thin wrench nor a big clamp to hold the air vent, so I decided to leave it alone. I also flushed the whole system again, this time lifting the lever of the pressure feeder to allow external water pressure for quicker flow. However, even when the lever was fully open, the pressure in the boiler was never above 20 psi, and I think when I did that last year, the pressure was much higher that it actually triggered the relief valve (30 psi). Anyway, my memory could be wrong on this. The boiler seems to operate fine and no leak at the pump (I used the original O ring on top and new rubber gasket at the bottom). No more of that banging sound has been heard since then. So far so good. I will give it more time to make sure that it is gone forever. Another thing I noticed is that my main water shutoff which is located below my kitchen sink started dripping some water in the past week or so, but now it seems to have stopped mostly. May be it was the water momentum that caused it to leak. Oh, there was not enough time to check for system leak yet, so I will do that in the future.
I am very glad that banging sound is gone, at least for now!
Really big thanks to all who have provided great advice and helps! If problem arises again I will continue to post here.