# My Pressure gauge is bouncing and my boiler is making a thumping sound ????



## machinistbcb (Nov 26, 2008)

I went out to fill up my tarm tonight and I heard a thumping sound in the boiler. I looked at the pressure gauge and noticed that is bouncing 3 or 4 degrees whenever I hear the thumping noise.  The Return water temp is 140 degrees, and the boiler is at about 15 PSI.  Any thoughts ????  We are having really high wind gust tonight in my area but I can't really see how that could effect anything.


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## trehugr (Nov 26, 2008)

machinistbcb, that sounds like a air pocket to me. Do you have a vent at the top of the boiler somewhere? I would suggest checking the easy things first.


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## boilermanjr (Nov 26, 2008)

I have seen/heard several different models and brands of wood boilers thump during hard firing.  Having discussed this with design engineers, it seems most likely that thumping is caused by small pockets of water flashing to steam.  I have "thumped" my own boilers for years to no detriment.  Do try eliminating air, if possible, from any bleaders that may have been installed on top of the boiler.  Most likely you did not hear the thumping on top of the boiler where the air would be.


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## chuck172 (Nov 26, 2008)

Why do some boilers of the same make knock, and others don't. I have a Tarm Solo40 that I can't get to stop knocking. I bleed the air from the coin vent on top of the boiler often, and it helps.
Next time the system is down, I will install and auto vent on the boiler.
Seems like it only happens when I have a full or almost full load burning real hot.


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## chuck172 (Nov 26, 2008)

Just had an idea! (before my first cup of coffee)
I wonder if it's possible boiler knocking can be caused by boilers that are not level. If you think about it, an un-level boiler might have a constant air pocket that would be tough if not impossible to vent.


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## NHFarmer (Nov 27, 2008)

I have been reading all these posts about this thumping sound,up untill recently I have not heard this sound.Then the other night with a nice hot fire and a full load I heard the thumping sound.I did vent the bleeder on the top of the Tarm and it did have a small amount of air in it.I have not heard it since.very strange


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## chuck172 (Nov 27, 2008)

Yep, that's how it started with me. A full load with the fan on. When it gets real hot. Bleeding from the coin vent seems to help, but the knocking comes back. I'm gonna get an auto air vent.
But I'm also thinking maybe the boiler isn't completely level. That might just cause a small air pocket. I'm really not satisfied with the way I leveled mine when I first set it up. There didn't seem to be any good points to level from.


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## deerefanatic (Dec 1, 2008)

Ever think of steam? I was having constant water loss. I.e. my pressure was always going down...... Couldn't figure it out... Well, I decided to shut off my two automatic coin vents......... Pressure has held now for over a week..... Go out and open them when the boiler is off and water is cool and you get nothing....... Open them when the boiler is firing hard, and you get a little hiss. My hypothesis is when you have a firetube heatexchanger (like we all have in our boilers) the tubes are so hot that the water right near them flashes to steam.... If contained, this steam will cool and turn back to water.... But if allowed to get into the open coin vent, it's vented just like air...... Hence water loss.........

Just my experience...


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## chuck172 (Dec 9, 2008)

I solved my knocking problem with my TarmSolo40. I thought that the boiler may not be perfectly level and being the boiler has a flat top, air was being trapped somewhere resulting in the hot water flashing into steam somewhere.
The coin vent is located on the front left side of the boiler. I made up (tightened) up on the front left corner leg adjuster. This raised the front left corner of the boiler pitching the top of the boiler toward the coin vent.
Air can now be completely vented and no more knocking.


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## NHFarmer (Dec 9, 2008)

Good to know and glad you solved the problem.Mine has been quiet since I vented it.Tonight should be a good test as it is really cranking,cold as a ??? tonight.


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## LeonMSPT (Dec 9, 2008)

Noticed something the other night when burning coal, and have heard it since with wood. Conditions are right, you can hear the over fuel gas fire igniting and going out, almost think "puffback". Not enough of an "explosion" so to speak to cause a puffback. In fact, I think it's exactly what I mentioned. The over fuel air/gas mixture is just right, when the temperature is just right, and it ignites and then goes out. 

Maybe this thumping is the fire in the gassification chamber getting regulated. Not quite the perfect air/fuel mixture at just the right temperature yet. So the "gas" fire is igniting, and then going out. 

Think about watching someone start a jet turbine, similar sound and feel. 

Just a suggestion. Could be all wet, but at least I'm not cold.


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## dougcarlo (Dec 9, 2008)

I still get knocking after purging several times.  I tried jacking the front up and the rear, still get knocking, maybe this summer when I do some more mods.  I will try and purge it again.  It does seem most of the knocking is on Solo 40's.   Doug


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## dougcarlo (Dec 9, 2008)

My knocking sounds like it is coming from the front right, if you were facing the doors to the right.  Like I said I jacked it up a little and ran it for a while, did the same for the rear.


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