I was called out on a Montigo Gas Fireplace Model B34DT 2 Serial #2-40825-128391. This equipment had been installed for several years and recently began having the pilot and main burner shut off together after the main burner had been on for 10-30 minutes or so.
This fireplace pilot was one of those with a clip on burner head that allows the pilot orifice to be removed for cleaning with an allen wrench (who's manufactures that, anyway?).
The pilot flame seemed a little smaller than I would have liked, but cleaning the pilot orifice did no good. The pilot gas was turned to max out the size of the pilot flame.
With the main burner off, the piloit flame decently engulfed the thermocouple, and there was no problem withy pilot outages.
Shortly after the main burner was turned on, some turbulence would be observed around the main burner flame, and the pilot flame would tend to be sucked towards the main burner. The thermocouple would no longer be adequately engulfed, causing the pilot outages.
This direct vent fireplace was top vented to the edge of a three story house on a long, fairly steep hill. Careful review of the installation standards disclosed no objections to this kind of installation.
So what was causing the turbulance, and how do you correct it? What additional information might you want or need to diagnose the problem, and where would you get it?
What I can think of to check:
Gas inlet & manifold pressures
T-pile MV with pilot only and burner switch on
Resistance of burner switch circuit
Proper log positioning
Proper burner position/cracks
Burner air shutter position
Valve EPU check
Valve operating head check
Resistance of any limit/safety switches & wiring
Obstruction or failure of venting system
If all that checks out, I would start looking outside of the appliance. Anything inside the home changed? New range hood, bath fan etc. Anything outside the house changed? Trees cut down, new house built nearby etc.
Where are you? Are you done yet? I got ONE more call for you.....
S.I.T. Makes those Pilots FYI.
It's got a 3 story verticle run? Check to see if it needs a restrictor plate if it does not have one already.
Thanks for the information that SIT makes those pilot burners.
<<It's got a 3 story verticle run? Check to see if it needs a restrictor plate if it does not have one already.>>
Actually, the fireplace is on the top of three floors, and the vertical termination is about eight feet above the fireplace. But it is on the edge of the building and the building is on the side of a fairly long and steep hill.
I did check the installation manual for correct installation of the vent, since I found this a possible weakness. No restrictor plate was discussed at all, and the standards permitted the fireplace to be on the edge of the roof of the building.
The SIT pilot has a primary air hole. Run a smoking pipe cleaner through it then blow it out with canned air.
Any chance the Fp is overfiring thus overheating the valve? A SIT valve is rated at 225F.
If this unit relies on a sealant on the pipe, it might explain why it worked for awhile then began to misbehave if the sealant fell out.
Can you reach the first joint at the starter collar and seal it with some refractory pookie (technical term)?
I've seen many units deoxygenate after yrs from a loss in seal, loss in glass seal, log moved, etc. Study the secondary airflow S/P--that might guide you to the problem.
Keep the fire inside the fireplace.
I was interested in seeing the lines of investigation other might have taken with the facts I confronted on this job.
Since I couldn't identify any actual problems with the ways the equipment was installed or any defects in the parts, I chose to call the manufacturer to describe the turbulent burner flame I was observing and getting any guidance the manufacturer might have on this kind of problem.
The first question out of the tech services reps mouth was to ask if the fireplace was top vented (yes). He said the likely cause of the problem was too much airflow through the fireplace causing the turbulance, and described a restrictor plate that should be installed in the vent.
I pointed out that no such restrictor plate was in the installation manual. He went right on to plan "B," describing making and installing a sheet metal box to install in the air inlet behind the burner and pilot, which would reduce the airflow through the fireplace.
I would conclude that the manufacturer discovered this kind of problem after the fireplaces began being installed, and came up with modifications and fixes to correct this weakness.
I'm familiar with other direct vent fireplaces numerous stories up on tall buildings and/or on steep, windswept hills that can have similar problems. Perhaps it's worth keeping in mind that manufacturer's don't always effectively anticipate the conditions their equipment can be exposed to.
It's probably worthwhile keeping an eye out for such problems in such situations.
I know for our brands they are all UL or OMNI listed and approved. If I remeber correctly there are a few UL tests that slam the caps with high winds (from a giant fan) to see what happens. They do it from a bunch of different angles and with different vent runs.
We run into the wind problems more with older units it seems like so maybe they are getting better at testing them for this flaw now?