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Rick
Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 20547
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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I have a munchkin 140mR2 nat. gas boiler. When the boiler

Customer Question

I have a munchkin 140mR2 nat. gas boiler. When the boiler ignites sometimes it will make a loud bang. I have replaced the ignitor with correct gap and performed coil cleaning inside unit with clr cleaner. I did not clean burner, although not sure how you would clean a burner on this unit without replacement. Do you know what could cause the loud bang on ignition? I receive no errors on the unit.
Submitted: 1 year ago.
Category: HVAC
Customer: replied 1 year ago.
Swirl plate on gas valve was replaced last year.
Expert:  Rick replied 1 year ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. If my initial response doesn’t answer your question then let me know and we can continue our conversation.

If you have a new igniter with the proper gap the a dirty burner is the most likely cause of delayed ignition (the bang). You to remove the burner cylinder to clean it properly. You'll need a new burner gasket to put it back together.

Customer: replied 1 year ago.
how do you clean the burner?
Expert:  Rick replied 1 year ago.

Vacuum it out and wire brush the burner cone if any of the holes in it are clogged

Expert:  Rick replied 1 year ago.

You have to remove it first. Of course if there are any defects in the cylinder then it should be replaced

Customer: replied 1 year ago.
burner cone looks like a brillo pad wrapped around a steel cylinder, not sure about wire brushing it.
Expert:  Rick replied 1 year ago.

You have to use a fine soft brush if it's clogged up. Usually a brass bristle brush. You certainly wouldn't use a stiff steel wire brush. Also carefully tapping the burner can dislodge the debris.

Expert:  Rick replied 1 year ago.

The "brillo" is on the outside of the burner. That's why you have to remove it first if you want to clean it.

Customer: replied 1 year ago.
I was told by another hvac tech. to use compressed air and vacuum, that is what I did. The furnace still has a loud bang, but only when it re-fires after it has been running and is hot, does not make the loud sound when it is a cold start.
Expert:  Rick replied 1 year ago.

You need to remove the burner to do this properly. Any loud bang is delayed ignition and not safe

Customer: replied 1 year ago.
I did remove the burner and replace the gasket, burner is crystal clean.
Expert:  Rick replied 1 year ago.

Then the only other likely thing is the electrode gapping/positioning.

Customer: replied 1 year ago.
What about using a combustion analyzer and adjusting gas pressure if necessary?
Expert:  Rick replied 1 year ago.

I would have assumed that was done during initial set up but it's worth a shot. I also wonder about fan speed since you say it now only ignites late when it's hot. But that's a control issue and there is no diagnostic for it.

Expert:  Rick replied 1 year ago.

I'm logging off for the night. If you have more questions I'll respond in the morning

Customer: replied 1 year ago.
it seems to light normally when from a cold start. But I noticed, if there is a call for heat it will fire up and run, when it reaches its high temp it shuts off and when the boiler comes on again because the zone is still calling for heat, this is usually when I hear the loud bang; sometimes are a lot louder than others. I installed the boiler in 2009 and never had a combustion analysis done on it because it seemed to run fine and did for quite few years until about last year. It was doing a similar thing and I had a hvac technician look at it and he said it needed a new swirl plate on the gas valve, so I put a new one on and it did the same thing. I then found out the spark electrode needed to be re-gapped it was way out of spec so I fixed that and it seemed to cure the problem. This year it recently started doing the bang again so I cleaned the unit and re-gapped the spark electrode, which broke when trying to re-gap, so I replaced the spark electrode. Boiler continued to make the loud bang, so now I have also cleaned the burner and replaced the burner gasket, I have to say though it does not bang as loud or as often as it did before I did the work to it this year.
Expert:  Rick replied 1 year ago.

You need a combustion test.

Customer: replied 1 year ago.
cleaned burner again and performed combustion test, boiler still makes a loud bang on ignition sometimes. HVAC Technician that performed combustion test did not know what was wrong with boiler.
Expert:  Rick replied 1 year ago.

You might want to contact HTP tech support. (###) ###-#### ***** this point the only thing I might try is replacing the burner.

Customer: replied 1 year ago.
Is it normal to have to replace a burner after 6 years of use?
Expert:  Rick replied 1 year ago.

No it's not normal. Neither is the condition you describe after trying all the remedial methods.