Flame Roll out fusible link blows out

alliect

I have a Viallant Boiler GA100-8 SPVD.  It is not a sophisticated boiler.  The net btu rating is 53k.  I do not know the age but it looks like it’s been kept in good condition.  It was in the house when I bought it 2 seasons ago.  I am located in the South Jersey shore.   
The flame roll out fusible link keeps blowing out.  The fusible  link is a micro temp G4AM0610. It is rated at 240C. (It seems the only place to get these is swimming pool supply Zodiac or Jandy)

I checked the flue from the heater to the cap on the roof.   It is clear.  No restrictions.
I removed the top of the boiler housing and blew compressed air down through the heat exchanger and I can see daylight down to the combustion chamber. It appears to be clean.  No visible restrictions.  No water leaks from the heat exchanger.    

I used low pressure compressed air to blow out the burners and vacuumed as best as I could without removing the entire boiler front ( the only way to remove the 2 burners is to remove the entire boiler front). I am certain the one burner is clear because I can easily see it through the pilot access.   Not sure about the other burner. 

I also drained the boiler and replaced the Taco circulator and the expansion tank automatic vent (Taco also).  

I recharged the system, ran the circulator for 20 minutes and set the thermostat.   The heater turns on without hesitation.  The flame is blue with a little bit of red mixed in.
 During the heating cycle the fusible link breaks the circuit and the heater will not fire back up.   It seem to me the link is doing what it’s supposed to do.   But what is the cause?   I thought maybe I have excess air in the water circuit but doesn’t the automatic vent expel this?   And the link blew out before I drained the boiler and recharged it.
Apparently the boiler is developing too much heat and I can’t figure it out.  
It obviously wasn’t the circulator pump.  

This really has me baffled.    

Any help is much appreciated.  

Thanks,

Dennis     

mattmia2

Did you check the draft? You need someone that understands combustion to figure out why it isn't drafting properly.

ScottSecor

Clock the gas meter and determine the actual gas input to the boiler, perhaps its overfired?

Are there any exhaust fans in the house or the attic? Is it possible you are accidentally forcing the combustion air downward instead of it naturally rising up the chimney?

Can we assume there is a damper on the outlet of the boiler that is in fact opening before the main flame turn on?

Is the breaching (smoke pipe) sized and pitched properly? Is the run more than a few feet from the boiler to the chimney?

Jamie Hall

It's a draught problem, not a water problem. It may be a problem with the flue or the breeching, or it may be a problem with getting enough combustion air. Has anything been changed in the house? Tightening up draughts? Adding an exhaust fan somewhere? You really need someone who can check the combustion overall, as @mattmia2 suggested.

EdTheHeaterMan

You may have a chimney issue. A clear chimney does not mean the chimney is drafting properly. Be careful when selecting a chimney contractor in your area. I have worked that area and have not found a decent professional chimney contractor in the Cape May, Atlantic, Cumberland county area.

This is a resource I have used before I retired. the above illustration is from this reference guide https://www.fieldcontrols.com/wp-content/uploads/2019/04/4338_ContractorReferenceGuide_2018.pdf

You might want to look at the chimney and what is surrounding it. Less that 5 minutes of operation with a downdraft is all it takes to blow that fusible link.

Depending on your location, there are supply houses that have that part near you. There is one on North Wildwood Blvd. between Rt 9 and the Parkway.

Is this the switch you are looking for?
It is available on Amazon. BUT. DON'T JUST KEEP KEEP REPLACING THEM. FIND THE PROBLEM!
https://www.amazon.com/American-Standard-Furnace-Thermal-FUS00620/dp/B00FA36CFO/ref=pd_day0_sccl_1_1/139-8456933-8346828?pd_rd_w=M0ivY&pf_rd_p=8ca997d7-1ea0-4c8f-9e14-a6d756b83e30&pf_rd_r=0TVR8QW7W2NNC1ECNQQH&pd_rd_r=2d9049e3-15cf-4bd9-81f7-ff800f819a78&pd_rd_wg=mpZQo&pd_rd_i=B00FA36CFO&psc=1

Ironman

It could be improper draft, too much fuel, too little air or the heat exchanger is not as clean as you think it is.

Id recommend that you get a KNOWLEDGEABLE tech that has a combustion analyzer and knows how to use it.

EdTheHeaterMan

alliect said:

I have a Viallant Boiler GA100-8 SPVD.  It is not a sophisticated boiler.  The net btu rating is 53k.  I do not know the age but it looks like it’s been kept in good condition.  It was in the house when I bought it 2 seasons ago.  I am located in the South Jersey shore.

I must correct you. You live DOWN the Shore!

EBEBRATT-Ed

Try find a contractor on this site. @EzzyT, @clammy , @JohnNY

Alan (California Radiant) Forbes

Good suggestions, everyone! I'd be checking the flue termination for anything blocking exhaust. It should have an approved termination piece. Roofers sometimes push it down too far and block proper drafting.

You can also remove the top and shine a light down to see if there are any obstructions.

SteamingatMohawk

@EdTheHeaterMan Ask Joisy, any exit! (Reference: Gambling TV commercial in upstate NY)

Turnpike 12Not the beach either.

SteamingatMohawk

Here seems to be the manual for your boiler.

https://www.manualslib.com/manual/508945/Vaillant-Ga100cs-Series.html#manual

Your unit has two safety switches, a flame rollout switch and a blocked vent switch. See the description on page 7. Since your flame rollout switch is tripping (one shot trip, then replace) and you don't mention the blocked vent switch (can be reset) tripping, it seems logical that venting is not the problem.

In addition to the suggestions in other HHers comments above, there are two situations I have come across that could contribute to the flame rollout switch tripping. One is the firing rate of the boiler could be higher than it should be if the gas valve outlet pressure is too high (3.5 in water column is common). The other, which is extremely unlikely but happened to me, is that insulation inside the sheet metal jacket of the boiler could have come loose and either blocks air flow or exposes the rollout switch to more heat. I can't tell if this is a possibility for your model boiler, but it is worth mentioning.

In any event, the fact the rollout switch is a one shot use, should tell you that the situation is serious and failing to determine and correct the cause is a risk that should not be accepted. Sorry, for sounding like a parent.

EdTheHeaterMan

@SteamingatMohawk indicated "Your unit has two safety switches, a flame rollout switch and a blocked vent switch. See the description on page 7. Since your flame rollout switch is tripping (one shot trip, then replace) and you don't mention the blocked vent switch (can be reset) tripping, it seems logical that venting is not the problem."

Sounds logical to assume that the blockage is in the heat exchanger, or below (since the blocked vent switch is not affected) so you will want to double check the heat exchanger. There is an exception to that rule. If there is a down draft that is significant, the cold air from the chimney can cool the flue gasses to a point where the Roll-out switch will fail without the blocked vent switch reaching the trip temperature.

I would still look at getting the chimney cap repaired. That partially missing cap can act as an air scoop causing an accelerated down draft.

Mr.Ed

Fix the cap then "FA-ged-a-BOUD-it"

bucksnort

My Burnham XG power vent boiler would blow them about every 2 years. I extended the mounting screw so the fuse set back about an inch from OEM. Haven't blown one in 20 years. The vent terminated with a T cap out the West wall so I've thought maybe a good gust of wind overpowered the blower and back drafted? No scorch marks so I don't know. What I did learn after cleaning the burners and forgetting to re attach it and it was laying wired up and grounded against the boiler jacket was it let out smoke from the relays and transformer when I powered it back up real good but never blew. I still have a spare ready to go.

SteamingatMohawk

@EdTheHeaterMan Assuming the draft arrangement includes mixing with room air (like my HB Smith boiler), wouldn't a downdraft cause the combustion air to "spill" out of the duct into the room? That might be detectable.

@bucksnort making the fuse further from the heat source compromises the fuse function, reducing safety. I suggest you check the actual temperature at the proper fuse location to see how close it is to the fuse melting point. What would an insurance inspector say if you had a claim and that was discovered?

mattmia2

This whole thread makes me really wish someone would explain or tell us where to look to understand combustion and draft instead of just saying you need someone who has been trained. Surely someone has written it down somewhere.

Jamie Hall

I;ll see what I can find...

Big Ed_4

Do you notice any soot anywhere ? Carbonized boiler

EdTheHeaterMan

mattmia2 said:

This whole thread makes me really wish someone would explain or tell us where to look to understand combustion and draft instead of just saying you need someone who has been trained. Surely someone has written it down somewhere.

Combustion Air – (1) Air that is supplied to combustion appliances to be used in the combustion of fuels and the process of venting combustion gases. Inadequate combustion air can lead to dangerous problems. (2) The duct work installed to bring fresh, outside air to the furnace and/or hot water heater. Normally 2 separate supplies of air are brought in: one high (for ventilation) and one low (for combustion).

from: https://www.usinspect.com/blog/combustion-air-what-it-why-it-important/

Draft - is the measurement of the chimney effect or stack effect related to a natural draft chimney. Wikipedia explains Stack effect as follows: https://en.wikipedia.org/wiki/Stack_effect Stack effect or chimney effect is the movement of air into and out of buildings through unsealed openings, chimneys, flue-gas stacks, or other containers, resulting from air buoyancy. Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences. The result is either a positive or negative buoyancy force. The greater the thermal difference and the height of the structure, the greater the buoyancy force, and thus the stack effect. The stack effect helps drive natural ventilation, air infiltration, and fires

Field Controls is a company that manufacturers equipment for the HVAC industry relating to combustion air and controlling draft and venting for combustion. This contractors guide has been helpful to me in my professional career in selecting products to safely provide combustion air and safely vent byproducts of combustion with natural draft chimneys and with power venting and direct venting gas and oil fired appliances. https://www.sidharvey.com/documents/UNI-02374_Broc.pdf

Pages 22 to 27 deal with combustion air. Pages 28 to 37 deal with natural draft venting thru chimneys of both the masonry and manufactured type.

I hope this is somewhat helpful. But to many non professionals (and many pro also) it is difficult to understand unless you see the invisible movements of air and combustion byproducts in your minds eye. A molecule of air (oxygen or nitrogen or something else) may travel from outside your home thru a crack in the wall near a window past the molding and slip by the insulation between the siding and the drywall. it then arrives inside the home and may become moist from being inhaled and exhaled by the family pet. It then finds its way down the basement steps into the oil or gas burner room. It is accompanied by millions of other molecules of carbon dioxide, oxygen, nitrogen and other airborne gasses and particles. The molecule now enters the combustion air inlet of the burner and is mixed with a hydrocarbon and becomes part of a flame. (OUCH THAT'S HOT!). As the flame extinguishes the molecule may have changed into a byproduct of combustion like "Carbon Dioxide" and travels thru the heat exchanger giving off its heat energy. It then passes into a vent connector and meets up with dilution air from a draft diverter or barometric draft control. Now this new group of "AIR" that includes dilution air, excess air from combustion and combustion byproducts all flow up the chimney and find themselves outside your home again.

EdTheHeaterMan

In a completely different home that same molecule of air finds its way close to a chimney and gets sucked in and travels down the chimney. As it gets closer and closer to the bottom of the chimney there is a small glimmer of heat and BAM! it meets up with byproducts of combustion that are spilling out of the draft hood and gets recycled past the combustion air inlet thru the flame, past the heat exchanger and out the draft hood. This happens three more times, in the combustion air opening, past the flame, thru the heat exchanger and out the draft hood. Each time with less and less oxygen for combustion. And each time there is more carbon build up on the heat exchanger. On the 4th trip this molecule breaks past this revolving door and out into the basement where there is an exhaust fan sucking very moist humid air from the flooded basement out the window and into the great outdoors again.

I could go on and on from house to house with a different trip every time. I have that kind of imagination to see in my minds eye how air and fuel come together and make a flame and expand to thousands of times greater volume, then cool down and get smaller as it cools and vents out so people don't get sick or die from CO poisoning. Can you use your minds eye to feel "If I were Air where would I go". High pressure moves to low pressure. Hot gasses or hot air is lighter than cold gasses or cold air. It's all done with the path of least resistance. And it does not always follow the arrows on the outside of a pipe. Those arrows need to be on the inside for the air to see where it is supposed to go.

Bob Harper

Draft is merely a pressure differential with respect to outside the stack. It's the driving force that makes chimneys work. The proof in the pudding, however, is "mass flow". Concern yourself with moving 'stuff' (air, heat, gases) up and out of the structure through the venting system. If you have a draft pressure of -0.02 wci, you don't have a draft issue- you have a flow issue.
Fire the unit for a few minutes until the draft pressure stabilizes. Block off the draft hood and note the effect on the gauge. Does it get much stronger? If so, you have a MakeUp Air situation. Fire the unit again. turn off the gas. If the draft pressure spikes, your liner is probably undersized.
You need to run combustion analysis to guide this process.
Look at the vent connector layout to the chimney. Is it the shortest, smoothest route possible? Are the pipe joints tight? Sloppy connector joints act as little draft hoods reducing draft pressure incrementally. Does your connector have restrictions or reductions? How about the transition into the flue? Fix the building and the chimney will work.