Home>Discussions>INSULATION & HVAC>Hydronic water heating system makes banging noise during heating cycle
9 posts / 0 new
Last post
Hydronic water heating system makes banging noise during heating cycle

I have a older hydronic hot water heating system (installed in 1976) that circulates the water once the water temperature get to the appropriate temperature and continues to circulate and heat the water as long as the thermostat requests heat. I have 4 zone valves and 4 thermostats. My problem is that during the heating process when the burners are on there is a banging or hammering noise that occurs from the boiler during the heating cycle. It seems to occur even when all zones are shut off and not circulating. The pressure in the line is about 10-12 psi and the heating cycle occurs from around 160 to 180 degrees F. I have bled the lines of the air but the noise is still occurs. Any causes for the noise and what are the solutions to solve this situation? Please advise.
Thanks, Joe

Re: Hydronic water heating system makes banging noise during heating cycle


The parameters you describe are within normal operating limits of the boiler.

The noise, unfortunately, could be coming from any one of ten possible causes.

It is often very helpful to first try and locate EXACTLY what part of the boiler is causing the noise.

For this, take a short piece of plastic garden hose, or any rubber hose a few feet long, put one end to your ear, and point the other end at different parts of the boiler when the noise is occuring.

Eventually, at one spot the noise will sound a lot louder than the others.

I'll list ten possible causes:

1) there is air trapped in the boiler because the little vent on the boiler is clogged (carefully take a pliers and loosen the screw-on cap if you have this type of vent on the boiler).
2) the air scoop vent or spirovent air eliminator on the supply pipe is clogged (do the same as first symptom, loosen the little screw cap on the top of the vent).
3) there are hot spots inside the boiler due to deposit accumulation inside the cast iron sections that are overheating.
4) The water temp is getting too high (over 190 degrees) near the end of the heating cycle so the boiler water is partially boiling.
5) You have Honeywell zone valves (or similar) that make a lot of noise when malfunctioning.
6) The expansion tank is waterlogged but the pressure relief valve is not opening at 30 psi as it should (check the water pressure on the boiler gauge while the boiler is running).
7) one of the circulator pumps is going bad and the bearings are howling.
8) you have an older, larger circulator pump like a B&G and the coupler has separated (broken off) from the motor & is banging.
9) something in the burner assembly has failed (including a failed nozzle, a failed fuel pump, a failed burner motor.
10) it's something else not noted.

As noted, try to isolate the noise to a specific spot on the boiler.

If you can post photos of the boiler and its components it would be helpful.

Do you have a large, B&G-type circulator pump?

What kind of zone valves do you have?
The name and model number of the boiler?
Is this a dry-base or wet-base boiler (on dry-base boilers the return water supply pipe usually goes into the boiler above the burner assembly)??

At what point does the noise occur: when the boiler first comes on, when the circulator first comes on, mid-way thru the cycle, at the end of the heating cycle???
Is the boiler making any "puff-backs" at the end of the heating cycle??

Re: Hydronic water heating system makes banging noise during heating cycle

Hi, JacktheShack
Please find listed below responses and photos of my heating systems.
Your questions:
1. Air not trapped in boiler because vent seems to be working properly – This vent has a tire valve cover, which I tighten down and after several days when I open it up air escapes
2. The only air eliminator is the one on top of the boiler called Auto-Vent Air Eliminator (Float Type).
3. Hot spots inside boiler, it seems that this may be the cause of the noise, which is like water boiling (hammering or pounding) inside the boiler. I tried to locate where the noise is coming from and it is from the inside of the boiler but it is difficult to isolate the location.
4. The natural gas heating elements turn off as soon as the water temperature hits 180 degrees F.
5. The zone valves are Taco Zone Valve 555-050RP and there are 4 of them.
6. There is a pressure gauge along side of the boiler in conjunction with the temperature game and the pressure remains 12 PSI.
7. I only have one circulator pump and it is a Bell-Gossett Booster Iron Body Series 100 F50.
8. The coupler and the motor are both new as of the early 2007. There is no noise coming from the motor or connection. The only noise is from within the boiler.
9. The boiler is natural gas and the entire burner seems to be functioning equally as far as burning volume.
10. The zone valves are described in 5 above.
11. The boiler is an American Standard GPM Gas Boiler GPM 6, Series 1BJ1 with input of 165,000 and output of 132,000.
12. The boiler must be a wet-base since the return is on the lower part of the boiler and the output is near the top of the boiler.
13. The circulating pump is pumping and there is no noise, once the flame starts the noise within the boiler starts in about 8 seconds and continues during the heating cycle for a few seconds after the flame shuts off.
14. Not sure what a puff-back is but did not notice anything at the end of heating cycle.
Thanks, Joe

Re: Hydronic water heating system makes banging noise during heating cycle
Re: Hydronic water heating system makes banging noise during heating cycle
Re: Hydronic water heating system makes banging noise during heating cycle

There is no 2X4" and there is no wetness of either oil or water.

Re: Hydronic water heating system makes banging noise during heating cycle

Yes, the location of the banging does seem to point to sludge or mineral deposits in the cast iron jacket.

But before settling on that, check the shape and color of the flame to make sure that it is blue in color and evenly distributed on the gas burners.

Do you have hard water in your area???

Have you had a service person come over recently to work on it; do you have a service contract???

If you check around, you can probably get someone in for $50 to take a look at it before you get involved in trying to make a fix.

If the service person verifies that minerals in the water jacket are causing the banging, you can then get an estimate of what it will cost to have it done, or attempt it yourself.

I would also have the boiler gas valve checked out to make sure the problem isn't because of a gas leak.

Sometimes just shutting down the boiler and draining the boiler water is enough to get some of the minerals out of there; the boiler is simply re-filled with water and bled for air.

There are water treatment products like 8-way (by Rector Seal) or Scalomatic (by Stewart Hall) that can be added to the boiler water & allowed to sit for a few hours.

The boiler water is then flushed and fresh water added to restart the system.

There is also Liquid Scale Remover or Lime Dissolver.

These items are usually available only at heating and plumbing supply houses.

8-way is widely used & cost only ~$10 for a quart; the boiler is shut down, a gallon or two of water is removed from the drain faucet at the bottom of the boiler, the vent fitting at the top of the boiler is removed and the 8-way is poured into the boiler using a funnel.

If you decide to use any of these chemicals BE EXTREMELY CAREFUL in handling them; they are injurious to skin, eyes and even inhalation; make sure the boiler room is well-ventilated, and wear safety glasses to protect your eyes.

Let us know how you make out.

Re: Hydronic water heating system makes banging noise during heating cycle

No that is a cement brick and it is dry no moisture of any kind. Basement is dry also.

Re: Hydronic water heating system makes banging noise during heating cycle

I have a very similar system that would gurgle and bang about 3 or 4 times every time it began a heating cycle. Like your problem, it was coming from inside the boiler. I was convinced it was air and tried bleeding and flushing my zones but that didn't work. Then I figured it was sediment and kettling but draining the boiler didn't remove much of anything. Well, my hot water boiler is over 50 years old and the whole system was aged and poorly maintained so I decided to do some upgrading and refitting. I added to the system a spirovent air eliminator, an auto-fill valve, a backflow preventer, a couple of ball valves, another drain bib and changed the old air expansion tank to a diaphragm Extrol type. I also moved my circulator pump and water fill from the return to the supply side. I cleaned and brushed lot of rust off the burners and the boiler tank. I cleaned up the aquastat and the relay and rewired everything. The copper pipes had a thin layer of sludge on the walls. I bought a descaler to clean out the system later, but when I ran the system after I was done refitting, the banging was gone and it runs so much quieter now. So, I did a number of things, any of which or combination could have solved the problem. I do know that the banging was NOT due to slude or deposits and kettling. There is perhaps some kettling happening, but it is very mild and sounds more like a kettle on the stove. I will be cleaning out the system with the Rhomar treatment kit I bought anyway. Perhaps there are some clues here for you.

Sponsored Stories

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.