New boiler pulsating / popping

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Old 12-04-14, 12:27 PM
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New boiler pulsating / popping

I recently had a new boiler installed for my two-zone slant-fin baseboard heating system.

The old boiler was 30 years old, and the new one is pretty much the exact same model, but with electronic controls. However, I am running into a tricky problem that I can't seem to pinpoint.

When running any one of the two zones, boiler works fine. Heats up to 180F and restarts at 160F as long as the heating call is in effect.

When running both of the zones simultaneously, things don't go as smoothly. Below is a detailed explanation;
-Boiler heats up to ~155F and the boiler starts pulsating until the PRV opens (obviously water boiling in the boiler)
-Boiler temp skyrockets to 230-240F, until it comes back down to about 210F when the pressure drops enough to allow replenished water to re-enter the system and cool the boiler back down.
-Boiler restarts at 160F and repeats the process.


I have checked a few things;
-Fill valve is filling the system to 12psi as it should. It is not overpressurizing the system
-Expansion tank is set to 12-15 psi (checked with the boiler water drained when it was cool).
-Both zone pumps appear to work effectively, as the return piping heats up shortly after the zones are activated.
-System pressure does not exceed 20psi, until the popping noises start, then it pulsates higher.


Items to note;
-We never had this issue with the old boiler. Nothing new was installed except the boiler, nothing else. All piping and accessories were rerouted to the new boiler (Same locations since new one is similar to the old one). Only exception is new draft damper and drain valves.
-I currently have the max boiler temp set to 150F with a restart temp of 130F. This heats up the place fine, but I'm not happy that something is not right.

Please help! I've spent hours trying to troubleshoot this but haven't made much progress.
 
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  #2  
Old 12-04-14, 01:21 PM
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Have you tried calling the installer back under the warranty?
 
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Old 12-04-14, 01:57 PM
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Please list the manufacturer and model number of the new boiler. Also, several well lit and in focus pictures of the installation would be helpful. Probably don't need close-ups yet but need to see how the entire system is piped.
 
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Old 12-04-14, 06:09 PM
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I oversaw the installation. I have installed boilers in the past without issue.

It is a Burnham P206. No photos at the moment but will post as soon as I take some.
 
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Old 12-04-14, 06:17 PM
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Check the arrow on the pump. The pump should be pumping away from the expansion tank connection on the supply side of the boiler and the arrow should be pointing away from the boiler.
 
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Old 12-04-14, 06:48 PM
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Yeah, sounds like a bassackwards pump to me too.

Wouldn't be the first time!
 
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Old 12-04-14, 08:20 PM
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Both zone pumps are on the return side and feed the boiler. Arrows on the housings are pointing as such. Expansion tank is on the outlet side of the boiler. I suspected a backwards pump as well, but this doesn't appear to be the case. The boiler temp rises at a slower rate when both zones are on, not at a faster rate (which would be the case if zone flows oppose each other).
 
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Old 12-06-14, 06:21 AM
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It sounds like air trapped in the boiler. Is there an air separator in the outlet piping?
Sid
 
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Old 12-06-14, 01:09 PM
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Yes, air separator is on boiler outlet side. Appears to be working fine. I power purged boiler and both zones.
 
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Old 12-06-14, 01:46 PM
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If the boiler operates fine with either zone but not both , could it be that the flow through the boiler is to much ?
 
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Old 12-06-14, 02:25 PM
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If the boiler operates fine with either zone but not both , could it be that the flow through the boiler is to much ?
That would typically cause the boiler to not heat up to temperature, rather than overheat as it seems to be doing.
 
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Old 12-06-14, 02:26 PM
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Will Be Free, where are the pictures?..........................

No photos at the moment but will post as soon as I take some.
 
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Old 12-06-14, 03:23 PM
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I reread your symptoms , sounds like the heat exchanger is getting so hot the boiler water is flashing to steam.
 
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Old 12-06-14, 04:02 PM
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sounds like the heat exchanger is getting so hot the boiler water is flashing to steam.
Which is an indication of low or possibly reversed flow.
 
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Old 12-06-14, 04:40 PM
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Please post some wide-angle photos of the boiler and surrounding piping. Maybe we will notice something, or maybe not. But otherwise, we are seemingly just throwing out hypothetical thoughts and theories, which are dismissed as impossible.

Here are some additional thoughts. You seem to have installed the boiler yourself, or at least supervised its installation? Correct? Without posting good photos, I'm afraid you are pretty much on your own.
 

Last edited by gilmorrie; 12-06-14 at 06:45 PM.
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Old 12-08-14, 04:50 AM
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Finally got around to getting some photos this weekend.


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Old 12-08-14, 05:23 AM
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The two pumps are cutting off the flow to the boiler because there is not enough length of pipe between them , result there is less flow to the boiler when both are operating then when either one is pumping .
 
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Old 12-08-14, 05:33 AM
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saves,
I'm not sure I understand your logic. Having the pumps closer together shouldn't cause less water to enter the boiler.

At the worst, if both pumps are on there will always be more flow through the boiler vs only one pump being on.
 
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Old 12-08-14, 08:02 AM
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When both pumps are running, the suction pressure will drop below what it is with just one pump running. This may be causing the pumps to cavitate. With two pumps in parallel, that can lead to oscillation.

The suction piping isn't ideal - it would be improved if the suction piping were larger. It would be even better if the expansion tank were connected to the suction side of the pumps.

What is the system pressure? If you jack it up, does the problem improve?

P.S. The popping noise you described is typical of pump cavitation. The suction pressure drops below the vapor pressure of the liquid, forming a gas bubble, which chokes flow. The bubble collapses, causing the noise, and flow is restored. The whole process repeats itself rapidly. There may be damage to the pump impellers.
 

Last edited by gilmorrie; 12-08-14 at 08:14 AM. Reason: P.S.
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Old 12-08-14, 08:53 AM
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Both zone pumps are on the return side and feed the boiler
Ummmmm... no, I don't think so.

If my eyes are not deceiving me... and they might be... it appears to me as if you've got the pumps pumping into the SUPPLY OUT of the boiler and the boiler RETURN is being used as the SUPPLY.

In other words, the boiler and not the pumps is backwards... in either case, the flow is reversed from design through the boiler.

Or am I seeing things?
 

Last edited by NJT; 12-08-14 at 11:18 AM.
  #21  
Old 12-08-14, 11:21 AM
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I'm seeing the same thing. Shouldn't the flow out be on the upper section of the boiler? Looks like the flow out which is on the left side (rear) in the pictures is on the lower section of the boiler.
That can't be right.
 
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Old 12-08-14, 12:17 PM
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Yeah, it's wrong. I studied the pics a bit more and looked at the maual for the boiler after I posted and am convinced that it's backwards.

The pumps are pumping into the supply out of the boiler. The return is the port at the lower left.
 
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Old 12-08-14, 12:24 PM
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NJTrooper, Tom - You are right!

I pulled up the boiler manual and the flow is running opposite of the design, and I know exactly what is happening now;

Water enters boiler through outlet (where thermocouple is), and continues to get heated as it now goes through the boiler and out the inlet (where it is now much hotter than what the thermocouple reads), causing it to overheat. It is probably running at ~212F when the thermocouple is reading ~160F.

I wish I could give both of you a big squeeze for your eagle eye!

Looks like the plumbing buddy I used to help me here swapped the orientation of the pumps, either that or the inlet and outlet ports was swapped between the old and new model boilers.

Is it ok if I just switch the pumps to work in the opposite direction? I don't see any new issues arising if I do.
 
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Old 12-08-14, 12:58 PM
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Is it ok if I just switch the pumps to work in the opposite direction? I don't see any new issues arising if I do.
You have 'flow check' valves in the system and if you reverse the flow, those will be backwards and won't open.

You could manually open them, but you may end up with 'thermosiphon' problems... which would (or could) overheat the home.
 
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Old 12-08-14, 01:01 PM
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The flo-control valves will then be backwards and stop the flow.

By the way, I don't know why you need flo-control valves with zone pumps, provided the pumps themselves have integral flow check valves.
 
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Old 01-16-15, 12:17 PM
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Don't mean to bump the thread - just want to report that the problem was fixed by flipping the pumps and check valves in the opposite direction.

I will take the blame for the error - as I purchased the same model number boiler as was installed prior, and didn't realize the inlet and outlet ports were swapped on the newer model. Meanwhile I told my guys to just swap out the old one for the new one, and trusted there would be no issues. Lesson learned!
 
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Old 01-16-15, 01:03 PM
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as I purchased the same model number boiler as was installed prior, and didn't realize the inlet and outlet ports were swapped on the newer model
Twas ever thus that the return comes in on the bottom and the supply goes out the top.

Thanks for letting us know!
 
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