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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Insufficient gas flow to main burner on Lopi gas fireplace

Customer Question

Urgh.....original question gone to the black hole of the Internet

Issue: Lopi Spirit B-vent natural gas stove. Cannot get sufficient gas flow to main burner.

I have two of these stoves, one not functioning correctly. This allows me to compare working to non-working. The stove in question worked fine when I shut it down last summer, now giving me grief.

Originally when I turned the problem stove on, pilot would not stay on, so took stove apart and cleaned thermopile and thermocouple of white ash. Millivolts at connections to gas control valve went from < 100 to now 500. Pilot now stays lite and engulfs both thermopile and thermocouple. In my functional stove the mV are mid 700s', but those thermocouple/thermopile were replaced last year with a Travis pilot assembly retrofit, so its not apples to apples. In both stoves, the mV drop drastically when burners are on (not sure why, at the limit of my handiman expertise).

Stove can be triggered to go on with both thermostat and ON switch, but flames are barely 1-2 inches in back and not at all in front of firebox. Took stove apart again and blew out main burner assembly. No change. Adjusted vent dial and also air shutter inside fire box. No change.

At this point am at a loss for an explaination. I am clearly getting gas to the main burner, just not enough. I can't find a technical manual on line. I have user manual, but it's not much help.


Submitted: 4 years ago.
Category: HVAC
Expert:  Phil replied 4 years ago.
All work to be done by licensed professional. WE KEEP GOING UNTIL YOU HAVE THE INFORMATION YOU NEED, I come and go. This is step ONE.

Hello, welcome to Just Answer!

Good work so far, to answer your question about the MV dropping when the gas valve opens, the solenoid in the gas valve is sapping the voltage.. thats normal

The low fire issue is likely a bad gas pressure regulator,...

Buy four feet of 1/4 inch clear soft plastic tubing and one 1/8" male pipe to quarter inch hose barb adapter, screw that into the gas line ahead of the gas valve after you have the tube about 3/4 full of water and red food coloring. There should be an eighth inch plug screwed into the pipe in both locations so you do that,

If no plugs I need the full model number of the lopi unit so I can look it up.

then bend the plastic tube into a U shape, and measure the distance between the two columns.

If its natural gas the pressure should be in the max 14" range not less than 7 inches there. and 3.5 inches down stream from the gas valve at that test port

Let me know what pressure reads you get, we can go from there,

Customer: replied 4 years ago.
No problems with gas pressure to cook stove, furnace or other Lopi furnace. When you speak about the gas valve do you mean at the wall, which turns the gas on/off to the Lopi stove, or the control valve on the stove itself? On the stove gas control valve there is an inlet and outlet.
Expert:  Phil replied 4 years ago.
Hello again, I am referring to the gas valve powered by the thermopile in the Lopi itself

It will have gas pressure test ports for inlet and outlet pressure.... or the pipes screwed into the gas valve, will have eighth inch plugs screwed into them

without a model number I can't tell which

The pressure regulator is either ahead of the gas valve by a few inches, or built into the gas valve,

The pressure regulator is disc like with a raised center section, three or four inches in diameter, no wires attached,

Customer: replied 4 years ago.

Here is the manual for the Lopi Spirit DV gas stove.


If I understand correctly, I remove the two screws, labelled in and out, to check the pressure? They are on the front side, top and bottom of the gas control valve, which has the Hi/Low dial for flame adjustment.on its face.


On pages 33-34 of the manual it also describes an orifice which fits into the fixed shutter. Should I first remove that and see if it is partially blocked or is the orifice pretty large at this location?

Expert:  Phil replied 4 years ago.

Hello again, I can't see that valve from here but if those 'screws' marked in and out, are actually 1/8" pipe plugs, (actual measure about 3/8" with pipe threads inside) then those are likely the gas pressure test ports

You can try connecting a U tube manometer to each of those as mentioned earler... do the hook up with gas valve OFF to the unit, then turn the gas on and see if the manometer reads 7 to 11" column of water at the IN plug, if so, thats the right plug for testing inlet gas pressure.

If thats not low, then test the outlet gas pressure with the U tube manometer hooked up first, then light the pilot and turn the unit on so the gas valve opens, and read that pressure, generally tthat should be in the 3.5 inch water column range,

I suspect it will be much lower, and that the cause will be a defective gas valve, Try adjusting the flame height knob, if that does not increase the outlet pressure the valve is bad... or the valves inlet screen is badly clogged, there is a very thin chance of that however.

There is some risk here, this work must be done by a trained gas appliance specialist who would use an electronic type gas pressure instrument instead of a U tube in most cases.... with a U tube if you drop the open end, all the water drains out and gas will come out the end of the tube, and if you do not shut the gas off within two or three seconds you could have gas entering the room. if you left it that way long enough it would be an explosion hazard.

I do not think you or your service man are likely to make that mistake but I do have to caution you,



The orifice at the fixed air mix valve is fairly large, it is not likely to be clogged,
I suspect the gas valve, and a reading well under 3 inches water column...

Notice page 17 with advice to call the dealer if the flame conditions are not right. That is because the manufacturer does not want home owners to work with the gas valve... the pressure tests i mentioned should be done by a trained gas appliance person. If that person finds the outlet gas pressure below 3 inches water column and the inlet gas pressure is over 7" water column, then the gas valve is bad and needs factory attention or replacement,

Let me know what you think, we can go from there,