Any advice for a loud banging on a hot water system??

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Old 12-21-10, 07:21 PM
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Any advice for a loud banging on a hot water system??

Hi everyone, This is my first posting and I hope someone here can help. I have a home that use hot water, baseboard heat. It has an Ack-O-Matic boiler, it looks very old but not sure how old. I couldn't find a model number on it.

My problems with the system started last fall. The Armstrong S-25 BF motor was making a lot of noise so I bought a spare to keep handy in case it went out on a cold night. This February I was out of town and my wife called to tell me that the heat on the 2nd floor would not shut off (90 degrees in the bedroom!!). Also the pressure relief valve had blown and dumped water all over. So I had a friend of mine replace the pump until I could get home. When I got home I found that the zone valve to the bedroom was stuck open and would only shut manually. 2 different valve would only open manually. So I had my HVAC guy replace all the zone valve since I figured they were all the same age and would all be going (Erie Controls V8043 replaced with new Honeywells). That was the end of the heating season so I assumed everything was OK. It's a 5 zone system 3 zones on the 1st floor, 1 on the 2nd, 1 on the 3rd.

This year when I fired everything up all worked well except that now when a zone valve shuts off there is a loud BANG shortly after the thermostat would kick off and the zone valve would close. The BANG is associated with the valve going off but the BANG comes from further down the line. I placed a towel on the hot valve and held it while my wife turned off the thermostat, I placed one hand on the valve and the other a couple of feet further down the line. It sure felt like the BANG came from further down the line and not at the valve.

The pressure tank is an Xtol SX30. There is always a bit of air in the tank (smells REALLY bad). I put a tire pressure gauge on the pressure tank and when heat is not called for my pressure gauge will not move. When hot water is circulating the pressure reads 16 psi on the tire gauge.

I cleaned out the water regulator and also replaced the blow off valve.

The pressure in the boiler runs from 18 to 22 psi and the temp runs between 140 and 160. I can't get it to go hotter. Is my Aquastat bad?

We have bled the air out of the lines until my fingers bled (not literally) and at my HVAC guys advice emptied and refilled the boiler twice. He also says he has double checked the flow valves and they are all OK.

My HVAC guy says he has talked to a dozen of his peers and everyone is stumped. It's getting awfully expensive as he keeps coming out to try and figure out what the problem is. I am a super light sleeper and this BANGING is keeping me up all night.

I thought that if I could raise the temp to 180 the BANGING might stop but I can't do that unless I drop another $150 plus labor on the new Aquastat.

Does anybody here have a thought as to what the problem might be?



Thanks
Martin
 
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Old 12-21-10, 07:44 PM
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Originally Posted by MartinL View Post
I put a tire pressure gauge on the pressure tank and when heat is not called for my pressure gauge will not move. When hot water is circulating the pressure reads 16 psi on the tire gauge.
If your tank had air in it, the pressure would not ever be zero. To get a meaningful pressure reading, the tank's water side must be completely deprssurized. Depending upon your valving, this may entail depressurizing your whole system and draining down to the level of the tank. Then, and only then, can you pump up the air side with a bicycle pump. (With a 3-storey house, I would go for about 18 psi.)

Since your tank seems to be mostly depleted of air, it's possible that the rubber bladder is leaking - if so, it's new-tank time. I don't think raising the system temperature would help.

The expansion tank, if it's not depleted of air, will help cushion the water hammer associated with sudden valve closure.
 
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Old 12-21-10, 08:00 PM
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There is air in it but with no hot water moving through the system it's so low it is not measurable. You can hear )and smell) it coming out when you press the tire valve but it is very low. Your explanation makes perfect sense though and I would have never thought of that. Thanks! Guess I will start looking at getting the tank replaced.
 
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Old 12-21-10, 08:11 PM
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Air, not water comes out...maybe your expansion tank is good?
Depressurize as Mike suggested, then pump it up (to 18PSI) to see if it holds air, then re-pressurize your system with water.
 
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Old 12-21-10, 08:23 PM
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Martin, this procedure is probably the easiest way to recharge a pressure tank while still connected to the system. Do this first:

=======================

1. Shut off boiler and allow to cool to under 100F.

2. Shut off water supply line to boiler.

3. Drain only enough water from the boiler drain to drop the system pressure to ZERO. REPEAT: DO NOT COMPLETELY DRAIN THE BOILER! ONLY ENOUGH TO DROP THE PRESSURE TO ZERO!

4. With an ACCURATE tire pressure gauge, check the air charge in the tank on the air valve opposite the end of the tank that's connected to the system. If ANY water comes out of the air valve, the bladder inside the tank is shot and the tank needs replaced. If no water comes out the air valve, and the pressure is less than 12-15 PSI, continue to step 5. If the pressure is OK, turn the water supply to the boiler back on and repressurize the system, turn the power back on to the boiler, no service is necessary.

5. Using a bicycle pump, or a small air compressor, add air to the tank until you have 15 PSI air charge.

6. Check the boiler pressure gauge again, and if it has risen off ZERO, drain some more water from the boiler drain until it is again at ZERO.

7. Check the air charge on the tank again. If it is below 15 PSI, add air to the tank until it is at 15 PSI.

8. Repeat steps 6 and 7 until the boiler stays at ZERO and the tank stays at 15 PSI. At this point, the tank is properly recharged and the water supply can be turned on to re-pressurize the system, turn the power on to boiler and return to service.

============================

I don't mention in this procedure what you should be pressurizing the system to, but you have a THREE story home? You might want more than 12-15 PSI in that tank...

How many feet is it from the bottom of the boiler, to the highest pipe in the system ? I would guess that 18 might be a bit on the high side... that would get you to 32' ... I am guessing that the system height might be like 25' and 15-16PSI would do just fine.

This is ALSO the pressure that your system should be pressurized to WHEN COLD. The pressure will rise when heated, and that pressure rise is controlled by the EXPANSION TANK.

The pressure that your boiler gauge reads when COLD must MATCH the air charge in the expansion tank. (Doesn't need to be EXACT, but close)
 

Last edited by NJT; 12-21-10 at 09:06 PM.
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Old 12-21-10, 08:26 PM
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The BANG that you hear is very likely WATER HAMMER when the valve closes. I'm guessing that it might only happen when more than one zone is calling for heat, and one closes... while the circulator pump is still running.

The first thing to check... and this is not as uncommon as it might seem...

ARE THE NEW VALVES INSTALLED IN THE CORRECT DIRECTION?
 
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Old 12-21-10, 08:28 PM
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at my HVAC guys advice emptied and refilled the boiler twice
Crazy... ya know the definition of insanity? A: Repeating the same action and expecting a different outcome.

Don't do that anymore!
 
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Old 12-21-10, 08:41 PM
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One last thing... it is HIGHLY LIKELY that your pressure gauge is NOT ACCURATE. Boiler gauges are from the DEVIL... they will drive you completely nuts if you believe them... so be prepared to verify that gauge accuracy if stuff doesn't make sense when the system is up and running.
 
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Old 12-21-10, 08:45 PM
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What a great site! Thanks for all the info!

NJ Trooper-
I think he was trying to fill the system differently each time. He thinks that there is an air pocket somewhere in the lines and was hoping to eliminate it.

He also said that he double checked to see that the flow was going the correct way. I didn't see any arrows on the valves. I know it's a total noobie question but how can I check the flow direction if there are no arrows? I'll go look again...

Thanks again to everyone who has posted replies, very nice to find a community this helpful.
 
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Old 12-21-10, 09:04 PM
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There should be a flow direction arrow embossed on the side of the valve body. Grab one of honey's makeup mirrors if you can't see both sides...

BTW, please tell us the 'height' of the heating system (question above) so we can advise what the system pressure must be.
 
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Old 12-21-10, 09:13 PM
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I just checked all the flow valves. They do have arrows on them, couldn't see them in the dark and the two old ones I still had did not have arrows-go figure. Anyway, the arrows all point away from the boiler and to the rooms they are heating so I guess they are OK.

I mentioned to my HVAC guy that I did not think the temp/pressure gauge was correct. It looks really old and I thought that one time I saw condensation inside of it. I guess that I will get one of those tomorrow as well and try and repressurize the tank as per your instructions. I agree about them not being very accurate/prone to failure.

It is 21' from the pressure tank to the highest baseboard. There are only 2 baseboard units on the 3rd floor. One 3' on the 3rd floor itself and a 4' one on the landing between the 2nd and 3rd floor 5' lower. The temp on the 3rd floor is almost always at 55 degrees because we never go up there,
 
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Old 12-21-10, 09:36 PM
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Anyway, the arrows all point away from the boiler and to the rooms they are heating so I guess they are OK.
Even backwards they will still pass water, so the fact that the stuff is heating ok is not conclusive. They will BANG like hell if they are installed backwards though...

If it's water hammer, you will get one LOUD BANG... and in extreme cases you may get a smaller bang immediately afterward... and it will sound sorta 'metallic'...

You said they are pointing AWAY from the boiler... so that would be the HOT SUPPLY OUT of the boiler, and into the system side, correct? If installed on the RETURN side of the boiler, they should point TOWARD the boiler...

Which side are they installed on?
 
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Old 12-21-10, 09:41 PM
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By the way, I think what Mike said earlier about having to replace the tank is going to turn out to be true... but try recharging it first, and if the valves are in fact installed correctly, it may turn out to be the problem with the water hammer...

There is one other 'trick' to try with the valves, but it's a last resort... so don't anyone say anything about the springs until the tank is recharged...
 
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Old 12-21-10, 10:13 PM
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If it's water hammer, you will get one LOUD BANG... and in extreme cases you may get a smaller bang immediately afterward... and it will sound sorta 'metallic'...

Yes-It's a loud BANG and it does sound metallic. And it does only bang once when I turn down the thermostat.

You said they are pointing AWAY from the boiler... so that would be the HOT SUPPLY OUT of the boiler, and into the system side, correct? If installed on the RETURN side of the boiler, they should point TOWARD the boiler...
Which side are they installed on?


Exactly. They are on the hot side out and not the return side.

After listening to you guys I think it will be the pressure tank. I will try to repressurize it first but what you are saying makes total sense.

I am in awe of the knowledge here! Should come to Cleveland and teach all these guys a thing or two. One of the largest contractors told my guy that my problem was "a dream come true" because he could spend (bill) hours and hours chasing this down. Of course unlike you guys he didn't have a clue as to what the problem could be.

Here is a new development-The temp on the other zones are turned down. Only one zone is active right now. The banging is not as loud as usual and as the night goes on the banging is getting quieter and moving closer to the valve. In other words when I started this thread the banging was very loud and sounded like it was in the end of the run. Now it sounds like it is substantially quieter and is coming from a baseboard much closer to the zone valve.
 
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Old 12-23-10, 08:19 PM
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Update and a big thank you

Today I repressurized my tank according to NJ Trooper's instructions.

NJ Trooper-Thank you very much for those instructions-you definitely saved me some cash. The tank seems to be holding well for the time being but I will keep my eye on it.

After repressurizing the tank the banging was still there. After staring at the system for about 30 minutes I checked all the zone valves again and they were all pointing in the same direction. I checked the circulator motor again and still could not find an arrow on it. So I pulled out the old pump and compared it side by side and found that the flow on the new pump was reversed. So I disconnected the new pump, rotated the flange and the banging is now gone. Been running it all day and it's quiet as a mouse.

I would like to thank everyone who replied again, I learned a lot about my heating system this week that I would have had to otherwise pay someone to do.
 
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Old 12-23-10, 08:58 PM
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found that the flow on the new pump was reversed.
Oh man... so the flow through the zone valves WAS reversed, but not because the valves were! We shoulda picked up on that.... it's not the first time it's happened.

It MAY be the last time that I don't ask for pics though! Cuz I think once we saw it it might have been spotted...

So now that the tank is properly charged, you should be able to pressurize the system when cold to 12-15 PSI, and it should go up to 20 max (probably less) when hot, right?

OK, good deal, you learnt us a lesson too! Thanks!
 
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Old 12-24-10, 07:26 AM
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Reading back to the original posting...
Was it your friend who unknowingly did you in when he swapped the pump?unish:
 
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Old 12-24-10, 08:08 AM
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I think it was... when Martin said the pump was backa55wards, I thought... 'hmmm, I don't remember reading that the pump was changed...' and went back and looked... sure enough there it was! I guess we all missed that point.

All's well that ends well... but let's all take it as a lesson to READ CAREFULLY!
 
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Old 12-24-10, 03:05 PM
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It was my freind who accidentally reversed the flow on the pump. I can't really blame him because he is a handyman and not a HVAC guy. It really was an honest mistake and HVAC guy did not notice it either. In my experience many times has it been the smallest most simple things that wreak he most havoc.

Thanks again guys and Happy Holidays to all!!
 
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Old 12-24-10, 03:44 PM
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HVAC guy did not notice it either.
But he would have been more than happy to milk your wallet dry!

One of the largest contractors told my guy that my problem was "a dream come true" because he could spend (bill) hours and hours chasing this down
Shame on him!

Merry Christmas!
 
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