Pilot goes out

haroldD

Have a problem with the pilots going out on these two(40 gallon atmospheric vent) water heaters, the vents are 3" they go into a 4x4x4 wye that goes into a ( 7" into the chimney)7x6x4 wye the 6" then picks up two 80 % efficient fan assited furnaces 1 ( four tube) the other( 3 tube) both burners have a 4" vent they are tied into a 6x4x4 wye.There was a combustion test on the water heaters one is running 80.3% efficient and the other 81.3 % efficient the draft at the breech on the water heaters were 0.05 wc,stack temp 512,co2 10%,o2:5.7%,co 27 ppm, i put some pictures in what should I look for?,the gas company is baffled, I'm just trying to help the guy out, not the original installer do not do furnace work.

Geno_15

It might have great draft

when you're in the room with the door open, try and simulate real world situations, are there any other pieces of equipment in the room or building that may run intermittently??? Blowers, exhaust fans, etc??? Make sure you've got CO detectors in the building. Is the chimney built right?? Can it be getting downdrafts at times ??????????

justme

pilot

Are Both pilots going out? If it is just one unit, it could be the thermocouple. If it is both units, I wonder if the doors on the hot water heaters are still in place and if not, could be a draft. Also, just might be gas pressure. Chek the pressure for each unit and test it on onnother appliance and see what the difference is and also how much it should be. Hope this helps.. Pure speculation

Weezbo

there is a blocked air vent in the last picture...

yank the white foam out (located above and to the right of the 4 square recptacle, emt and humidifier) and re test ...just to satisfy my curiosity.....:)

Dale

Inputs

How does all the inputs look on the vent tables. What are the furnace and heater inputs? First I guess I would check that and make sure the manifold is large enough. As the other post suggested it's always a good idea to check draft under all conditions. As to the pictures there is very little connector rise on the heaters. You may be able to solve this just by bringing the heaters in above the furnaces as close to the joists as a sheet metal spacer will allow. That way you get a foot or so of vertical rise at each heater. The fan assists have long single wall connectors, a bad idea. B vent is the only correct choice for the longer connectors. You need to test the water heater pilots by starting the furnaces on at a time, the resistance of the y connect may be more than a short circuit down the heater vent. The other possibility is gas pressure, has a gauge been used at the heater inlets when the furnaces start? Please let us know what you find.

don_52

good catch Weez, ...

There's another blocked window or "vent" on
the other side up where the pvc and the steel column
intersect.

To address the issue directly, when pilots "drop out"
(repeatedly) it indicates either insufficient make-up
( combustion ) air or inadequate venting or both,
precluding a problem with the pilot burners, thermocouples
and gas valves. (dirt, dust , fouling, etc., looks like
quite a bit of concrete dust down there)

Funny the number's don't look too bad?

That depends on what the weather's been like and how
often the systems have been cycling. (keeping the chimney
warm), bet it happens more often in colder weather than not,
doing a check a 32D F can be quite different from -5.

Further, folks would need to know the a:)"gross btu" input
of all combution devices in the space, b:) the total cubic
footage of the space (basement) LxWxH.
c:) is the chimney lined, b:) height of chimney d:) total
square inches of the two opening to the left and right
of the system. ( perhaps more )

Now, having said all that, there is "no substitute" for
having a "qualified individual" looking over the system,
someone has to see it "first hand" to be able to recommend
a corrective course of action, that's just the way it is,
it's difficult if not impossible to diagnose a problem like
this by " remote control".

In the "perfect world" everything would be done right the
first time, now enter the real world, doesn't happen, the
folks that have looked at the system may just not be up to speed on the current "best practices" if your friends are lucky, just providing adequate make-up air "might" solve the problem.


This isn't something that must be treated lightly, right
now it may seem only a "nuisance", yet it it can be quite
dangerous and potentially lethal.

Finally, as Weebo said; the opening above the humidifier
"may be" a good first step, it sure "looks as if" it was
included to provide make-up air for the system.

be safe, don

Unknown

WHAT IS THAT

register doing on the return to the furnace? With that in place when the blower on the furnace comes on you are getting a pressure change in the room. That wiil definetly cause the pilots to go out.

It is also a code violation as you can not get return air from the same room as you are getting air for combustion.

If there is any spillage of flue products before the pilots go out that is being pulled into the return and feeding back into the home.

GET THAT THING OUT OF THERE NOW!!!!

Unknown

Further comment

after looking at the other pictures and realizing this is a fan assited with atmospheric water heaters.

1. I would remove the water heaters from the connection to fan assisted furnaces.

2. Put blocked vent switches on the draft hoods of both water heaters,

3. Make sure I have plenty of air for combustion based on measurements of the area and BTU inputs to equipment.

4. To be real safe provide mechanical means of bringing in air to the space and interlock with all the appliances.

Fan assisted furnaces with water heaters is a real problem now days. I know the code allows them to be vented together but it really is not working.

That draft reading that was taken was that before or after the draft hoods and were the furnaces running at the time?
If it was before the draft hood directly into the water heater flue it is excessive. If it was taken after the draft hood I would be curious to see what it was before the draft hood, I would not be suprised if it was "0" or less in other words no draft.

In my other post I mentioned the register in the return. Do some combustion testing with furnaces off, then on but no system fan, then with the system fan running. I would be curious to see what you have. Do this before removing the register. Then block the register and do it again and see if there is some difference. I would still remove the register no matter what.

Bob Harper

Thanks Tim for catching the return

I was in a hotel last night so I just saw these pics & almost passed out at that damned grille on the return. Folks, this is how to build a backdrafting machine. The return ducts need to be sealed with mastic and tested. The filter change needs to be interlocked to the appliance controls( per'54), the vent connectors on the water heaters should be straightended out, the right hand furnace vent connector does not have 1/4" per foot slope, the chimney is unlined, and the gas piping/inlet pressures are probably inadequate for all this load. Seal that damned vent immediately on that return, then shoot the rotten **** that put it in there. Gee, can you tell how I feel about this crap? If I was responding on this call, I'd get out my manometer and run a Worst Case Depressurization test and assess for makeup air needs.

Once you've addressed the venting and pressure regimes, I'd do some gas pressure analysis:
Turn off everything else in the house that's LP. Take a static reading with just these pilots 'on'. Now, fire the water heaters one at a time, noting the inlet pressures. If you don't have pressure taps, remove a cap on a sediment trap and install a gas cock with a pressure tap downstream. Fire each appliance individually, then collectively, then everything on the grid at full load. Do you still have 11 wci under full load? I'll bet not.

Since this is LP, you need to survey the supply up to the house. What size tank? ASME buried or DOT vertical? How much fuel in tank? Per a % gauge or old psi gauge? Does this have 2 stage regulation per NFPA 58? Is the second stage regulator at the tank or close to these appliances? How many feet of what kind of piping btw the second stage reg. and these appliances? If any soft copper used, is it K, L, or ACR? Have you inspected the pilot burners? Is the pilot flame adjustment up high enough but not too high? What wci do you have to the pilot under full load? What is the lockup pressure of the 2nd stage reg.? Does it creep? Has anyone inspected the 2nd stage reg. for freeze-up when the pilots drop out? Add up all the BTU inputs and cross check with the 2nd stage reg. to see if it is even rated to handle this load.

I'd also check the rest of the ducts for balance. Since this nut put a grille in the return right at the fan, it probably means he isn't getting enough air back and this is his hack solution. Great. Let these people breathe in all the polluted basement air as well as backdrafting the heaters. How much you wanna bet the returns are panned out joist bays and stud cavities?

Ok, I'm calming down, now...

Unknown

In addition to wht Bob and I have

suggsted. It would probably be a good idea to take some millivolt readings on both water heaters. Just one more thing to check, in fact it is a ggod idea when you are doing the pressurization test in the combustion zone to monitor the affect on the pilots.

don_52

ready, fire, aim

Tim,

You just shot the wrong guy, I have nothing to do with
"that installation" nor do I know where it's located.

Good call, wrong target ~|;)

Can only wonder what else is wrong?

Bob Harper

Timmie's training site

Just goes to show how something that sounds so simple can get rather complex. A lot to consider in this case. For those not well versed in assessing thermocouples, Tim has one of the best mini-lessons "on another site". Tim, can you post the link? No sleep from being on the road.

Hey Tim, we oughtta invent a datalogger for thermocouples with inputs for gas inlet & manifold pressures, stack temp., Co, Co2,dewpoint, excess air, and draft, room depressurization in Pascals, and maybe some rollout and spill switches. Now, if you Really wanted to hit it big, figure out a sensor for women's menses to correlate against service calls.(Please, it's only a joke!) We could become gazillionaires and retire to the islands where they don't have mechanical devices that need techs to fix! ;-)

Larry F

Timmie's dead on...as usual

As E. Fudd says, Sompin' scwewy goin on awound heea. The page is so huge i may have missed some text but I never saw the dimensions of the space the equipment is in. The first thing i usually look for when a return is cut in at the furnace is whether supply air is being brought back in to the space to attempt to replace what's getting sucked out. The vent slopes may not quite measure up but then again I've seen water heaters draw even when the vent was run from the top of the heater down to connect at a cleanout near the floor (strange but true). Unless I've missed some code amendments, the fan-assisted furnace can still be vented into a tile-lined masonry flue as long as it's propely sized and common vented with at least one drafthood appliance. Although I agree the equipment installation is far short of stellar, the fact that both water heaters are having pilot outages is likely due to either a restriction or blockage in the flue or just an unholy marriage in the vent configuration after they enter the flue (IMHO). My first thoughts are that the direct causes of the outages are due to either a negative pressure in the room with the blower on or the furnace inducer overpowering the natural draft water heater vents and causing their burners to "float out". Either case I'm thinking a severe backdraft and floating burners. Everything needs to be on and room doors closed and I believe the mystery will be solved. Not ignoring the installation issues here and I concede that a combination of wrongs could add up to a given failure but in this case I think it's a specific issue that is the root. ie; that dang Goodman is venting out through the water heater drafthoods.

Larry

Unknown

Don, it was not directed

at you, I was just picking up at the end of the posting. Sorry about that.

MIKE6

venting

I would first call ao smith to see if there is a recall on the pilot assembly.They had problems with nat gas and had replacement kits a few years ago.To make the venting better i would move the 2 water heaters above the 2 heat vents.This will get you out of the fan assist stream x 2.It will also give more vent rise off the awh,6" vertical is ideal min.I would make the single wall vent B vent off the 2 furnaces.Under 100,000 btus S/B B vent to the chimney.Get rid of the open vents on the return air ducts to both furnaces.Also place the water heaters on a solid foundation,there is a gap between the blocks.
Mike

Harold Carmichael

I went back

took some readings my connector is loose on my combustion analizer so some maybe scued, I did test with my draft gauge also, my draft gauge was reading -0.01 basement air when all the appliances were running, the digital one was reading -0.04 at the peek, I also did a combustion analisis on the furnace, I have no numbers on the furnaces because i could not locate the rating plate or model number, so the three tube unit is running:eff:80%,excess air:176.3%,stack temp:295F,primarytemp:55.6f,o2:13.8%,co2:4.7%,co:24ppm,co air free:71ppm,draft:0.11wc.
Furnace #2 4 tube:Efficiency:79.6%,Excess air:143%,stack temp:335f,Primary temp:55.6f,O2:12.8%,CO2:5.3%,CO:12ppm,CO AIR FREE:31ppm.Draft:0.05wc.I have more pictures I am making a list for the warm air contractor to make the repairs, thanks for the help so far, the house does have gas leak and co alarms in the basement.Tim that millivolt test can you give me the 411 on that.Thanks again.

Unknown

Harold, here you go

I am often asked about troubleshooting a thermocouple on gas systems. This will be a permanent reference that will give a step-by-step procedure.

A thermocouple is a device used to satisfy pilot safety on many 24 volt gas systems. The thermocouple is a device made up of two dissimilar metals. They are joined together at the tip (Hot Junction). When heat is applied to that hot junction a small millivoltage is created. This develops because of temperature difference between the hot junction and what is called the cold junction. The flame has to envelop the upper 1/2" to 3/8" of the thermocouple and the tip should glow a "dull red". If the flame is adjusted to a sharp flame it will glow "cherry red" this will cause the tip to be welded and eventually the thermocouple will fail. The flame should be adjusted to a soft blue flame, not roaring or lifting. The normal millivolt output is 25 to 35 millivolts, on some you may even get up to 35.

The other part of this safety pilot system is the electromagnet (power unit). It is if you will the LOAD and we can say the thermocouple is the SOURCE. The electromagnet is made up of a coil of wire and "U" shaped iron core.When the thermocouple is heated and the millivolts generated the coil will be energized and create a magnetic field. The magnetic field will cause the "U" shaped iron core to be magnetized, it in turn will hold open a seat allowing gas to pass through.

When this system malfunctions it typically causes the pilot to go out and the gas will not flow. The first thing that should be done when arriving at a pilot outage situation is to do some visual checks.

1. IS THE PILOT LIT?
2. IS THE PILOT CLEAN? (NOT YELLOW)
3. IS THE PILOT HITTING THE UPPER 1/2 TO 3/8 OF THE THERMOCOUPLE?
4. ARE CONNECTIONS TIGHT?
5. IS TIP DAMAGED?
6. IS THE COLD JUNCTION BEING HEATED BY THE PILOT OR MAIN BURNER FLAME?

Once those things are addressed it is a good idea to take some millivolt readings. It should also be mentioned that many times it is the policy of some to replace the thermocouple on a call and clean the pilot. It is not a bad thing to do, however it is statistically about 85% of the time it is the thermocouple giving the problem. It is the other 15% of the time that taking readings can solve other problems.

You need a multimeter with a DC volt scale as the millivolts generated are DC volts. There are four readings we are going to take they are

OPEN CIRCUIT - this is taken with the thermocouple disconnected and the meter leads attached to the outside of the thermocouple and the other meter lead attached to the tip of thermocouple. The pilot-on-off knob will have to be held manually to take this reading. This measures the output of T'couple the readings must be above 17 to 18 millivolts.

* CLOSED CIRCUIT - This measures the millivolts used by the coil in the electromagnet . A rule-of-thumb is this reading should be roughly half of the open circuit. It is taken using an adapter screwed into the magnet and the thermocouple screwed into the adapter.

CLOSED CIRCUIT LOAD - This reading is taken the same as the previous reading except the burner is now on. With a proper flame this reading should be about the same as the previous reading. With a lifting main burner flame or excessive drafts or chimney pull, this reading may reduce from previous reading (flame being pulled away from the thermocouple). With the cold junction being heated this reading may increase. If the "cold junction" is heated excessively it will break down.

DROP OUT - This is the final reading. It requires the pilot to be blown out. It measures the ability of the magnet to hold under reduced MV input. A good unit should drop out below 6 MV's - normal is 1 to 2 MV's. The allowable "drop out" time is 180 seconds yes three minutes. It is more likely to be a minute and half to two minutes. There will be an audible "click" when the magnet shuts down.

* THE CLOSED CIRCUIT READING REQUIRES A SPECIAL ADAPTER THAT SCREWS INTO THE MAGNET ASSEMBLY TO ALLOW CONNECTION OF THE METER. AN ADAPTER CAN BE PURCHASED FROM ANY ROBERTSHAW DEALER THE PART NUMBER IS 10-038 THERMOCOUPLE TEST ADAPTER.

A normal set of readings

OC- 30 millivolts
CC- 15 millivolts
CC(load) -15 millivolts
DO- 1 millivolt

The best way to be able to diagnose these readings is to use MILLIVOLT CHARTS these can not be displayed here but I can provide them if you e-mail me.

I will add a little more to this later but for now this will be a good start.

Steve Miller

What Tim said

I'd patch where the grill on the return plenum and make sure you have plenty of combustion air. Plus, it's not vented correctly with the 2 fan assisted furnaces. I don't have the A.G.A gamma tables in front of me but I believe the chimney should be lined with a metallic liner and the tee's need to be Type B as well as Type B vent connectors to both furnaces. The connectors to the water heaters need to be 4" and at least 26 ga single wall keeping in mind clearances. You can see rust on the single wall tees because of the flue gases condensating as it hits the cold chimney. I do believe the problem is the grill on the return along with poor combustion air creating negative pressure on the water heater's venting. Check your pilots on the water heaters. The pilot orifce might have some crud in it causing a weak flame. You can verify too with a millivolt reading on the thermocouples.

Steve M

Steve Miller

What Tim said

I'd patch where the grill on the return plenum and make sure you have plenty of combustion air. Plus, it's not vented correctly with the 2 fan assisted furnaces. I don't have the A.G.A gamma tables in front of me but I believe the chimney should be lined with a metallic liner and the tee's need to be Type B as well as Type B vent connectors to both furnaces. The connectors to the water heaters need to be 4" and at least 26 ga single wall keeping in mind clearances. You can see rust on the single wall tees because of the flue gases condensating as it hits the cold chimney. I do believe the problem is the grill on the return along with poor combustion air creating negative pressure on the water heater's venting. Check your pilots on the water heaters. The pilot orifce might have some crud in it causing a weak flame. You can verify too with a millivolt reading on the thermocouples.

Steve M

ScottMP

Could Someone PLEASE

Make the photo smaller so that others can read this Most informative post with out scrolling back and forth.

Scott

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