nuisance pilot-light outages

Neider

I have two pressure trolls installed on my Weil Mclain EG 75 series 4 boiler for a one pipe system. I think one of the pressure trolls is just a back up for the other.

Anyway, whenever I try to run my system at between 1/2 to 1psi, my pilot light blows out. The Weil Mclain manual warns of this with relation to running the boiler at low psi using a pressuretroll and labels it a nuisance outage. I was wondering if installing a vaporstat would allow me to run the boiler at my desired lower pressures without the 'nuisance outages' occurring on my pilot light. (currently it is set at 11/2 psi cut in and 3 psi cut out :(

Thanks.

Steamhead (in transit)

That's the first time

I've heard of low steam pressures killing a pilot light!

The steam pressure should have nothing to do with the pilot system. I'd suggest getting a good gas tech to look at it. Try the Find a Professional page of this site.

A Vaporstat should work fine and save some gas.

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Tom Hopkins

Agreed

Absolutely nothing to do with it.Something's wrong and it's not the pressuretrol.If the units in good shape consider having it converted to spark ignition rather than spending $ on T-couples,gas valves etc.

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Dan C.

pressuretrol

One of the pressuretrols is a backup and that one should be set higher because it will kill the pilot every time it shuts off on pressure

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Steamhead (in transit)

So are you saying

they tied that pressuretrol into the thermocouple circuit? Never seen that.....

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Unknown

I can see,

a second pressuretrol as safety back-up for the main burner(a requirement anyway), but how would you even wire this up to kill the pilot too?

Dave

ScottMP

Me niether

I would think it has to do with gas preasure and blowing out the pilot when the flame shuts off, maybe a poor pilot flame.

I agree with Frank, I can't see how this has anything to do with the preasuretrol.

Scott

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tim smith

pressuretrol & pilot outage

My guess is that they are referring to standard pressuretrolls set that low may cause short cycling of burner, on and off etc and this may blow out pilot. With no tension against the spring at low settings, the switch tends to be a little unreliable. A vaporstat may be a good call, ?? Tim

Unknown

if I remember right...

Its was on the weil mclain HOT water boiler that had the high limit wired in series with thermocouple circut. What a PITA and replaced the pilot assy with a larger flame and rewired the secondary circut with extra safety cut off. No problem since.

Unknown

rjbphd may have-it,

I was curious so I did some digging on the WM site. Seems the EG 75 model uses the Robertshaw 7000 GV with a "thermopile" to the pilot burner, this in turn is wired through the high-limit switch. Certainly different from the conventional "thermocouple" I`m used to seeing. Don`t know why they went this route, but I`ll certainly remember. Short cycling shouldn`t "snuff-out" the pilot, but with the control wired through this it will.
Perhaps this is what Dan C. meant.
Thanks Ray.

Dave

Lyle C

Check and see if one of the pressuretrols is wired directly to a block on the powerpile (not a theramlcouple) . I still see alot of these boilers in the lowell area . One pressuretrol was the operateing control and the second was a safty wired into a block on the powerpile we usally set the safty about 10 psi if the boiler ran over for any reason this would shut it down .

Neider

Well, for everyone that doesn't think it's the pressuretroll, you may be right, but the Honeywell manual warns of this problem and calls it 'nuisance outages'.

I believe Tim was correct about the spring action causing teh problem. I don't know much about the mechanics of a pressuretroll but isn't it true that a vaporstat operates with a mercury switch?

Anyway, do you all think I can eliminate this problem by switching to a vaporstat. Seems Tim may know?

Thanks for all your replys. I will keep you updated.

Neider

Dan,
Can you tell me why the backup has to be set higher? According to my understanding, it functions in the same manner as the main pressuretroll. I believe it is just a matter of the way the back up was piped in line with the main that makes it a 'back up' and that it never functions unless the main fails? I could be wrong as I am just a concerned homeowner.
Thanks.

Dan C.

steamhead

I have seen it on millivolt systems a lot. Mostly Burnham. Never seen it on a thermocouple.

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Steamhead (in transit)

I've seen it on millivolt too

but this appears to be millivolt in disguise.

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Unknown

Second Pressuretrol

should be wired into the 750 Millivolt circuit as a safety to shut off the pilot. This was instituted by boiler manufacturers in place of the requiremnt for dual valve application (redundant valves). Powerpile valves are single seated and cannot technicaly be used on heating. The ANSI standartd however allowed for using and ECO tupe device (Energy Cutoff) similar to what is used on water heaters to shut the pilot off in the event of overtemperature. In the case of steam it is to protect against a runaway valve causing a build up of pressure and blowing the pop safety (15 pounds). The second pressuretrol should be set for 14 lbs off and 9lbs on (Set cutin to 9 and the differential to 5.

This is all covered in my manual on Powerpile Systems.

What is happening may require someone to do a set of millivolt readings on this system in addition to checking the settings.

Steamhead (in transit)

There you have it

from one of the best in the industry.

Question, Tim- on a heating system (no process application) is it necessary to let the second pressuretrol cut out that high? Remember, some air vents and other devices can only handle 10 pounds or so, above that they will fail. Since no steam heating system should ever need more than 2 pounds, wouldn't it make more sense to set the second pressuretrol to cut out at maybe 5 pounds?

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Unknown

Those settings

are the settings that the various boiler manufacturers gave in thier literature for set up. I am sure adjustments could be made as long as the perimeters functioned within both safety and operational limits.

The name that was given to these back up limits was "auxiliary limits". On Forced hot water boilers the setting on the aquastat limit was 233 degrees (F). On some of them it was a fixed temp and could not be adjusted, for example the White Rodgers series of relays 8D42A-701 thru 704 called the limit a "Pepi Switch". Honeywell relays L8148 L, M, N had the limit taped to the capillary bulb and the case was welded to the well so it was necessary on replacement to remove the entire relay and the well. The White Rodgers models are no longer available and can be replaced by the Honewell series.

Tim Gardner

Well, the vaporstat didn't solve the problem, but I'm glad I got it on there anyway. I got the guy who installed the boiler coming out to take a look. Thanks for all your suggestions, I printed them, hopefully they'll help if he can't figure it out.
I'll let you know how we solve it, if we do.

Unknown

Get in touch with me

I have a complete manual on troubleshooting self generating systems. e-mail gastc@cox.net or 401-437-0557.

yourchizzler

pilot going out

Hey guys I read all your suggestions, As long as the pressuretrol is not connected in anyway in the T-couple/ powerpile circuit, I would start looking at gas pressure and manifold pressure, and how this boiler is drafting, I would look at flue draft and combution air. Has the chimney been checked? Do the flames roll out on start up? If all is okay then maybe a bad gas valve? By the way has this boiler been combustion tested with a combustion anylizer? I have also seen T-couples that were in bad alignment/ getting to hot and kicking off the valve. Hows the pilot flame strong/lazy? Just some suggestions of what else could cause standing pilots to go out every now and then. Don't just focus on a mention in a manual, use your skills and you shall find the answer. good luck with your pilot problem. You should call a local pro to check your problem out.

Bob Harper_2

guessing

Instead of playing the guessing game, you need a qualified technician to perform a complete service. Since you have pilot outage, the one thing I haven't heard, which is the most common cause and will be picked up on a proper diagnostic check up is low inlet pressure. you need to record inlet gas pressures static, burning, and with everything else in the house going full bore. Then, record your manifold pressure, too along with MV readings.
If this is a thermopile only, you will need about 325 mv to hold the main operator open and the pilot. TP -TH/TP Ohms usually run about 8-10 +,- 10% on Robertshaw 7000 series valves. Now, close the TH to TH/Tp and see your millivolts under load. Are they over 80-100?

Don't get tunnel vision--look at the system holistically-gas, valve train, controls, venting--all.
HTH,
Hearhtman

Unknown

Let us try to

realistically get to the source of this fellas problem. This post goes back a couple of months.

First of all Tim Gardner what is the make of gas valve and the numbers on the gas valve? That will help to determine if it is in fact a powerpile (self generating) system.

Powerpile systems are tricky and require the taking of a full set of readings with a millivolt meter or meter with a DC volt scale.

Space does not permit posting my entire manual on these systems but believe me they are tricky and can fool you if you do not know how to diagnos them correctly.

Concerning thermocouples (30 millivolts) versus self generating (750 millivolts) they are similar only in the design to the hot versus cold junction feature for creating millivlots after that they are definitely two distinctly different systems.

I will post a guide to troubleshooting thermocouples in another thread for those who are interested.

Tim Gardner try giving me a call????

Unknown

On thermocouples

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.

Thermocouples from different manufacturers vary as to their dependability. The only thermocouples I recommend are made by Johnson Controls. The K15 and K16 series are the best. If you are having durability problems then use the K16RA which is a nickel plated high ambient or corrosive environment thermocouple. The Husky (K16) will fit most applications and for those that it does not the Slim Jim(K15) will fit.

To repeat the adjustment of the pilot flame to envelope the upper 1/2 to 3/8 of the thermocouple is important, the flame should be a soft blue flame not roaring which will cause the tip to glow a "dull red" versus "cherry red".

The combustion condition (excessive temperatures) in the chamber is also an issue and this will require a combustion test and draft measurement to insure that excessive temperatures are not being applied to the pilot. In some cases on water heaters it may be necessary to alter the pilot adaptation to get better quality performance. This however should not be done unless you have had proper training.

The possiblity of the equipment operating in a depressurization environment will certainly lead to thermocouple failure. In addition if the equipment is flued together with a "fan assisted" furnace or boiler this can lead to problems. There are solutions to this also but training is required.

The thing that I find is often a problem is the environment in which the equipment is operating. Many times corrosive chemicals and airborne contaminants are being drawn into the air gas mix and a checmical reaction takes place. This again requires attendance at a training session by a professional combustion person to help you to see the various affects this will have.

Last of all the failure to put all the doors and covers back in place on equipment. The failure to do this will cause an alteration in combustion air and the flame stability is affected.

The design of some equipment is also a problem. When there is high demand for heat (very cold weather) the temperatures that are created in the chamber have an adverse affect on the pilot and thermocouple system. The addition of the K16RA thermocouple can offer some assitance toward extending the life of the thermocople in this situation.

Insufficient air for combustion and dryers operating in close proximity to equipment also lead to problems.

Last of all and this is not directed at any one in particular but just plain lack of service personnel and installers knowing what they are doing.

My book "Circuitry and Troubleshooting" addresses many of the things in question here.