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Running water sound in hot water heating system

I did see there was a previous post concerning this subject, but am not able to find it so here's a new one. In the basement, we have a separate boiler system from the forced air HVAC that supports the rest of the house. There are 3 separate loops. One in particular sounds as if it has running water rushing through it. My husband found what he believed to be the high-point bleed valves in order to remove air. He held up rubber tubing to catch any excess water in a bucket below. Buckets of water ended up being removed from the system. I could see bubbles rising from the tube in the buckets of water so I do believe air is/was trapped in the system. I believe he said the water regulator was set to allow fresh water into the system at this time. He told me the system reads 12 PSI. To me, the rushing water sounds louder than ever. He disagrees and says it sounds the same (I think it's fair to share his opinion, too). I'd say it went from a trickling sound to a running sound. To me, the pipes also seem hotter. What do you think happened, if anything? Should we do any follow-up work?

Re: Running water sound in hot water heating system


From reading your post several times, it seems like you are doing exactly what you & your husband should be doing to correct the problem & expel the air; but check a few things out & try bleeding the rads/baseboard again.

1) Check the boiler pressure gauge--the gauge should read at least 12 psi to 15 psi---this is important because there has to be at least 12 psi water pressure in the system to drive the air out when you open the bleed valves; if there is less than 12 psi, open the valve that controls the water pressure to let more water into the boiler until you get at least 12 psi water pressure (this is also known as water "height" or water "altitude").

2) Make sure you go upstairs to the HIGHEST point in the boiler piping/baseboard/radiator system and open the little air valve on the highest baseboard/radiator--you may have to remove an end cover on the baseboard/radiator so you can access the BLEED VALVE with a screwdriver---hold a little paper cup near the bleed valve to catch any water that comes out---once water comes out, close the valve & go on to the next radiator/baseboard---remember that AIR always seeks out & finds the HIGHEST POINT in the piping/convector system, so this is where you have to expel the air to successfully BLEED AIR from the system.

Remember, even though you have 3 separate loops, you have to remember that during the heating process throughout the day, the 3 loops will MIX with each other because several loops will often be CALLING FOR HEAT at the same time and air in any of the loops will gravitate TO THE HIGHEST POINT IN THE PIPING SYSTEM because air is lighter than water.

When you open a bleed valve at the high point of the system you should hear A HISSING SOUND if any air was present at that point and it was expelled; as soon as you see water come out after the air, immediately close the bleed valve & go on to the next rad/convector---there's no need to end up with a bucketful of water from the rad/baseboard---your goal is to expel only the air---as the system runs thru the day & nite it will continually force the air to the highest point in the system; you can then go back the next day & once again bleed only the air from the highest convectors as just described.

If all else fails: If after performing the procedure just described you still can hear "water rushing sounds in the pipes", try turning up the different room T-stat on ALL 3 ZONES at the same time & run them for 15 minutes or 1/2 hour---this will allow the water in all the separate zones to mix freely & allow the air to gravitate to the upper part of the piping system---you can then try bleeding the convectors at the top of the system again.

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