# Detonation on startup



## jigs-n-fixtures (Feb 22, 2014)

We just had a new high efficiency propane boiler installed. Direct power vented. 

The folks that live at the Ranger Station are hearing "loud blasts like a shotgun shot", and and seeing a flash at the exhaust. 

The contractor who put it in and I both thought they were exaggerating until two weeks ago when he and I were standing in the parking lot and saw/heard it happen. 

So we know that we are getting detonation on startup. What we don't know is the cause, and solution. 

The manufacturer says we can solve the problem by repiping the gas line to include 12-ft of 3/4-inch pipe between the regulator and the gas valve. We have about 4-ft. 

The propane folks are saying that's crazy, we only need 10-diameters of the regulator discharge, or 7.5-inches. We have a foot before the first ninety. 

So, are either of them correct?

Anyone else have any ideas on what could cause the problem.

Small petty people have small petty Gods.


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## shlomy81 (Apr 23, 2012)

I gotta check ur gas pressure while it starts, or some manufacturer requires they the gas company should only use 2 separate regulators not 1


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## jigs-n-fixtures (Feb 22, 2014)

shlomy81 said:


> I gotta check ur gas pressure while it starts, or some manufacturer requires they the gas company should only use 2 separate regulators not 1


Thanks for the reply. 

The company that installed it had never done one from this manufacturer, and the installer and I spent lots of time reading and rereading the manual and installation instructions before he put it in, and followed them to a tee. 

We made an installation punch list, that included checking the pressure with a manometer before startup, during the start and during the run. Everything read fine during the commissioning/initial start, and we've checked it half a dozen times over the last month, since we got the first complaint. 

We're scratching our heads and out of ideas

Small petty people have small petty Gods.


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## shlomy81 (Apr 23, 2012)

What brand is it


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## Tommy plumber (Feb 19, 2010)

Make sure that the components of the gas train are in the right order. 

The gas pressure regulator should be upstream of all electric valves. It should be oriented correctly, that is to say, right-side up. 

If for some reason the regulator is downstream of the first electric gas valve, this may account for the flame rollout. When the electric gas valve is powered 'off', the gas pressure regulator will open wide. With the gas valve energized and open, the regulator will be wide open and overfeed gas to the burner. The gas pressure will regulate itself to the proper setting but not until the flame shoots out of the side of the burner.


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## wyrickmech (Mar 16, 2013)

What is the brand Fulton makes some that are hard starting and gas pressures are the problem most of the time.


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## CTs2p2 (Dec 6, 2011)

Any chance the unit needs to be field converted to LP? 

Most units come set up for natural and need a conversion kit to be run off LP..


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## BC73RS (Jan 25, 2014)

I'm wondering in the start up sequence whether the inducer fan is pre-purging as it should?


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## wyrickmech (Mar 16, 2013)

CTs2p2 said:


> Any chance the unit needs to be field converted to LP? Most units come set up for natural and need a conversion kit to be run off LP..


 good point that may be the issue


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## BC73RS (Jan 25, 2014)

Ranger Station was mentioned, what is the elevation? Could it be that orifice sizing needs to compensated for the altitude? .


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## Plumbworker (Oct 23, 2008)

What brand of boiler?
Most boilers are set up for natural gas and must be converted to propane via different ignitor and combustion settings..

Sounds like you're getting delayed ignition.. too much gas building up in combustion chamber during ignition.. Check gapping of spark rod... Some boilers will use a different type of ignitor depending on the fuel type one for LP and one NG.. check gas pressure and fuel air combustion settings with a analyzer the manufacture should have the correct Carbon Dioxide and CO settings for lp listed in the manual...


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## shlomy81 (Apr 23, 2012)

U gotta do a combustion test


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## PlumberDave (Jan 4, 2009)

The times I have run into detonation on high efficiency equipment has been from a failure of the of the flame arrestor screen after premix.


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## PLUMB TIME (Feb 2, 2009)

If you get PM magazine check out this months article on the "gas train" and flame rollout. perfect timing.


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## plumbdrum (Nov 30, 2013)

PLUMB TIME said:


> If you get PM magazine check out this months article on the "gas train" and flame rollout. perfect timing.


I seriously doubt this has a Gas Train, that's almost always found on LARGE boilers, and with a sealed combustion boiler you would have no flame roll out. Sounds like it needs to be tuned up with an analyzer like others have stated.

Sent from my iPhone using PlumbingZone


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## jigs-n-fixtures (Feb 22, 2014)

The factory rep came out for training and commissioning. 

What was happening was the volume of the gas piping between the regulator and the gas valve wasn't large enough. Not sure of exactly how this works. The gas valve actually sees negative pressure at start up. If there isn't enough volume in the feed pipe from the regulator to the valve you get an air fuel ratio that won't ignite until the regulator catches up. We increased the volume by adding an 18-inch long, piece of 2-inch as a sediment trap. The increased volume solved the problem.

Dignity, Honor, and Respect: Even when their, dishonoring disrespect leaves you indignant.


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## BC73RS (Jan 25, 2014)

Sounds as if the inducer fan was creating the negative pressure in the combustion chamber, the extra volume of gas in the 2"x18" pipe enrichened the air to fuel mixture to get the proper combustion.
Glad to hear the problem was solved.


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## Plumbworker (Oct 23, 2008)

jigs-n-fixtures said:


> The factory rep came out for training and commissioning.
> 
> What was happening was the volume of the gas piping between the regulator and the gas valve wasn't large enough. Not sure of exactly how this works. The gas valve actually sees negative pressure at start up. If there isn't enough volume in the feed pipe from the regulator to the valve you get an air fuel ratio that won't ignite until the regulator catches up. We increased the volume by adding an 18-inch long, piece of 2-inch as a sediment trap. The increased volume solved the problem.
> 
> Dignity, Honor, and Respect: Even when their, dishonoring disrespect leaves you indignant.


What brand of boiler is this..? And after the fix was the combustion properly dialed in?


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