Boiler pressure fluctuation


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Old 03-09-05, 08:54 PM
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Boiler pressure fluctuation

I usually help answer other peoples questions, but now I have one I can't figure out. I have a 1973 vintage American Standard gas fired hot water boiler, heating my small house with baseboard radiators. Heres the problem.. As the boiler heats up, I notice the pressure gauge begins rhythmically surging between 15 and 18 pounds, about three times a second. This continues as long as the burner is on, and for a short while afterwards. The boiler sounds like there are marbles inside, but the sound is quite faint. Other than this the system works fine.
Is this an air issue? All baseboards are hot, and seem fine, so I doubt the air would be there.
Any ideas would be appreciated
 
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Old 03-10-05, 09:38 AM
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Probably is air. Is there an air vent on top of the boiler or air scoop?
 
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Old 03-10-05, 12:19 PM
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No air vent on top other than the pressure relief valve, and the pipe up to the expansion tank, which has "some" water in it, as it should.
 
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Old 03-10-05, 01:59 PM
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The temperature of the boiler water is going too high. The water may not be circulating or the temperature setting is too high. Try a lower setting on the high limit. Nothing above 190 if possible.

Ken
 
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Old 03-10-05, 05:18 PM
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Thanks for the replies!
Ken, I have the high limit set to 180. Is this too high? This problem just started recently, and I haven't made any recent adjustments in the system, except the new Taco 007 pump last April. Is there a possibility that the 007 is too small? It replaced a B&G series 100.
I wonder if it is internal scale buildup in the boiler, yet the system water is extremely clean. I don't think the condition is hurting anything (or IS it?), but it is annoying.
Maybe I'll lift the PRV and see if there is a little air accumulated at the top of the boiler.
Any other ideas?
Thanks!
 

Last edited by Andrew; 03-10-05 at 05:20 PM. Reason: More info
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Old 03-10-05, 06:13 PM
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180 is fine. It sounds like boiling is going on in the boiler. We see that in low mass low water content boilers that don't move the water through them fast enough. The 007 should be a fine replacement for the B&G 100. I don't know what to tell you next.

Ken
 
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Old 03-11-05, 04:33 PM
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Andrew

This is a common problem with dry base boilers & nearly all gas fired boilers are dry base. You likely have some encrustation on the inside of the boiler right at the the bottom where the flames hit the boiler. A de-scaling might help but then, it might not.
 
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Old 03-11-05, 06:03 PM
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Thanks guys--
Yes I suspect scaling might be the problem. Now I need to figure out how to attack this. Would it be best to wait until spring, then drain the system and circulate some sort of diluted acid through the boiler? There is a flushing proceedure discussed in the manual (yes, I actually have the original manual ) which I could try. Hopefully leaving it like it is for another month or two won't hurt anything.
Thanks again!
 
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Old 03-11-05, 07:02 PM
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De-scaling

There are a number of de-scaling compounds on the market but I've never used any of them. Maybe Ken or Al have. Guys?
 
 

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