Enerjet boiler, flame in burner tubes

STEAM DOCTOR

Good morning. Have customer with above mentioned boiler and issue. I did a gas pressure test and adjusted to manufacturer recommended 3.5" WC. Did combustion test and everything is within acceptable specs (don't have numbers in front of me). Turned boiler on and left most burner tube was filled with flame. Turn off, waited few minutes and turned back on. The left most tube was totally fine but different tube had flame inside. Not quite as intense. Cycled off and on a few times. Sometimes, there was zero flame in any off the tubes. Other times, there was flame. Strange thing is that intensity varied and the the actual tune with the flame varied. Never more then one at a time but not necessary the same tube each time. 
1. What is the cause of this issue?
2. Solution?
3. Safety? Would assume that boiler is unsafe to operate under these conditions. 
All thoughts and ideas are much appreciated. TIA

GGross

It strikes me as odd that you could have only single burners firing, seemingly chosen at random with differing visual flame quality and the combustion test was within spec.

natural gas?

Silly question but did you adjust incoming gas pressure or the manifold pressure? what is the incoming gas pressure and is it consistent while the boiler is firing or attempting to fire?

What was the initial reason the customer called for service?

STEAM DOCTOR

All of the burners are firing throughout. Just some of the burners would fire normally and on occasion individual burners would have fire inside the tube. I have did not check incoming pressure, just manifold pressure. Was a no heat call and I replaced the gas control. Honeywell vr8200. Natural gas. 

SteamingatMohawk

Have you checked the orifices with the appropriate size drill bit? I had a consistent problem with my boiler for quite a while and nothing made a difference, cleaning the flame tubes, checking for obstruction in the piping from the gas valve to the tubes, adjusting gas pressure. I even used a copper wire occasionally to make sure there was no buildup ( like static causing dirt to be attracted (yeah, I know that's far out) It made no difference.

When I finally decided to "invest" in the correct size drill bit (size listed in my manual), the tube that was the problem was the only one where the drill hung up. Cleaned it and now everything is beautiful.

STEAM DOCTOR

I did not. But the randomness of it is puzzling. The burner tube that is working perfectly, will have flame in it on the next cycle and vice versa

EBEBRATT-Ed

Just the usual stuff. Check and clean orfices. burner tube alignment and gas pressure. If nothing shows up play with the gas pressure up and down a little and see if this helps. Draft ok?

Maybe the gas company is jacking some propane in there ...they do that during cold snaps. might be worth a phone call.

Also check the inlet pressure to see if it is steady. Two regulators could be fighting to control the manifold pressure

Steamhead

Try switching to a slow-opening gas control like a VR8200H or a step-opening one like a VR8200C. The old one might have been one of these, but you couldn't see it operate so you wouldn't know.

STEAM DOCTOR

@Steamhead Trying to wrap my head around this. The slow opening will initially have less volume of gas, but will also have lower pressure, potentially making it more likely for gas to end up trapped inside the tubes. I have a sneaky suspicion that I am missing something here. All thoughts are welcome.
@EBEBRATT-Ed. Draft is okay. Measured with combustion analyzer. Don't remember exact numbers. I measured manifold gas pressure and was steady at 3.5. Orifices are all clean. Did not measure inlet pressure. There is a Burnham Independence boiler in the same boiler room. Coming off same house gas piping. No issues whatsoever. I certainly hope they did not put propane in. Never heard of such a thing. This is in Queens New York.

STEAM DOCTOR

@EBEBRATT-Ed. There is only one regulator. The one in the gas valve. There is no regulator on the house piping. House in this area have low pressure coming into the house 

SuperTech

I've only encountered this problem with LP and the issue was low inlet pressure at the gas valve. 

EBEBRATT-Ed

@steam doctor

With low gas pressure in the street and antique gas piping in the street make it all the more likely the gas company could be jamming propane in there.......that's why they do it they inject liquid propane into the NG to keep the pressure up during high demand when they know the lines in the street are undersized.

Very common, they call it "shaving"

I would definitely check the inlet pressure, you're working off fluctuating street pressure .....who knows what that is.

Steamhead

STEAM DOCTOR said:

@Steamhead Trying to wrap my head around this. The slow opening will initially have less volume of gas, but will also have lower pressure, potentially making it more likely for gas to end up trapped inside the tubes. I have a sneaky suspicion that I am missing something here. All thoughts are welcome......

You're thinking of a flashback. As I understand it, for the flame to burn in the tubes like that, the ignition source is generally a bit of flame that rolls out momentarily. I've seen this get past the usual roll-out shield and ignite gas in a burner tube. It doesn't take much. This would also explain the randomness of the problem you're having.

STEAM DOCTOR

Much appreciated. Now that you mention it, I did observe a very brief rollout at times. For split second on initial light up.

Steamhead

STEAM DOCTOR said:

Much appreciated. Now that you mention it, I did observe a very brief rollout at times. For split second on initial light up.

That's all it takes.

If this is standing pilot, you want the VR8200H or C. If spark-to-pilot, it's the VR8204H or C. This assumes an input of less than 200 MBH.

Let us know how it worked.

STEAM DOCTOR

Standing pilot. Way under 200k. Will certainly keep you posted.

STEAM DOCTOR

Just to follow up (because I promised). Spoke to the wife, who said that she would speak to the husband, and would use the mini splits in the meantime. This is a small boiler for a relatively small addition on the house. So no real updates 😥😥.

SteamingatMohawk

What have you done about the occasional rollout?

STEAM DOCTOR

Boiler is currently turned off and gas line capped. So no rollout 🤣🤣