Munchkin

Mpj

<span style="font-size:16pt">I have a munchkin 199 which has been installed for about 6 years. I do the maintenance on it very every year. I was working in the basement and noticed the boiler was starting very rough (almost like a tiny explosion)</span>. <span style="font-size:16pt">I put on my Fryrite and all the numbers are in the allowable ranges. The CO2 was at 9% Co was 55PPM at high fire. The incoming gas is 7.92"WC. The unit runs fine after the burner starts. The exhaust and air intake are one of those stainless one piece units. There is no sign of cross contamination. Any help would be great.

Merry Christmas to all.

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Rich_49

199M

Just rebuilt one that is 8 years old doing what was described to me as a backfire .  Contact HTP and get the rebuild kit part number for your unit , order through your local; supplier . Also check the swirl plate in the fan assembly , may have dust and debris from intake impeding air flow to gas valve / burner . Worked very well for this rebuild , I replaced everything that came in the box including the ceramic backwall and refractory door plate after cleaning the heat exchanger very well .    Good luck .  Parts were reasonably priced , I was pleasantly surprised by the cost .

Mpj

Munchkin

Rich,

The swirl plate was/is clean and looks normal. There was nothing blocking the air inlet.

What did the rebuilding kit due? What parts did you change besides the gaskets?

Is this a problem HTP knows about?

Steve Whitbeck

reversion

If you have concentric venting ( one piece stainless ) then you are getting reversion.

The CO level should be a minimum of 75 at high fire.

It sounds to me like your boiler is running lean - thus - hard ignitions.

Mpj

Munchkin

Steve,

What exactly is reversion? I have never heard of it.

What is the best course of action?

Steve Whitbeck

reversion

Reversion - exhaust gas reversion is where the exhaust gasses coming out of the vent pipe get sucked back into the intake pipe.

NO high efficient boiler or high efficient MODULATING furnace should be vented with ANY type of concentric vent termination. They ALL cause exhaust gas reversion. When the boiler or furnace is being fired at full output it is USUALLY not a problem but when the unit modulates down to minimum firing rate the exhaust gasses don't leave the vent pipe with enough velocity to get away from being drawn back into the intake opening. The only time I use a concentric vent termination is vertically through the roof and then I extend the center pipe up another 12 to 16 inches. ( as much as I think I can get away with )

Exhaust gas reversion WILL destroy the boiler. It destroys plastic parts and circuit boards. It can even cause the stainless steel heat exchanger to get pin holes. The exhaust gasses after being drawn in and burned again cause very acidic condensate that CAN even eat into the stainless steel.

kcopp

There are a lot....

boiler out there w/ concentric flues...... they are all approved. Surprising that the cross contamination problem wouldn't come up in testing. Generally speaking the concentric units use the polypropylene piping (better) than the separate pipes that are PVC....looking to be less desirable and long term problems...

Steve Whitbeck

concentric

Kcopp -

Yes there are a LOT of boilers out there with concentric venting. AND they are an approved method of venting. BUT it doesn't mean it is the best way.

The boilers that are concentric vented are the aluminum parts nice a shiny?

Or are they dull and pitting?

Concentric venting is hard on the boiler.

TWO separate pipes is no different than one pipe inside the other as far as reversion is concerned.

I have been using a 45* instead of a 90* at the top of the vent pipe riser on the outside of the house for years. It is now starting to show up in install manuals. 

Just because the install book shows that you CAN do something doesn't mean it is the best way. Take the Munchkin boiler. The book shows it sitting on the floor. I have never done this. I have always raised them up on a stand or blocks so I could get at the drain line and so that I could get a decent pitch to the drain.

Mpj

Munchkin

Steve,

Thank you for your responce. I will look at the venting and see if I can remove the stainless steel plate and do like you suggested. Hopefully that will work out.

SWEI

Venting and reversion

If you intake through a wall and exhaust through the roof (assuming the boiler is approved for such a difference in pressure zones, which at least the older Munchkins were not) reversion becomes essentially impossible.

Jr_12

Delayed ignition

Has the problem been resolved? I would start with a thorough cleaning of the heat exchanger. Check the refractory and target wall for damage or sign of condensate back-up. Pull the burner tube off and check the burner gasket(R1 or R2?). Also make sure the unit is draining condensate properly. Normally I see burner/burner gasket problems being the cause for delayed ignition. Recirculated flue gases can wreak havoc on electronics, swirl plates, and blowers but I doubt it has much to do with your situation.

We set our units at 9.5% CO2 on high fire

Mpj

Munchkin

JR, I have not been back to this job. I will be there after the new year to do other work. I'm going to extend the existing vent to see if that helps at all( I will be the basement to keep an ear on it). The 199 is a rev2, all the components are just fine no sigh of cross contamination, swirl plate is good I changed the target wall and burn refractory about 8 months ago, condensation draining fine and the burner is clean. Unit is firing fine as per specs.I will let you know what happens after the new year. Thanks!