Mendota pilot won't stay lit

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.

jtech1

Member
Nov 2, 2014
22
US
Mendota DXV45 fireplace was installed last year. Worked great all season. This year turned on the gas, set to CPI, igniter ticks once/second. Pilot lights immediately. After about 30 seconds the pilot turns off. This cycle repeats. The igniter was still clicking every second all while the pilot was on. I am assuming the flame sensor (sensor with U loop at end, I assume) is not sensing the flame. I notice that the center part of the pilot is not touching the flame sensor, and I don't recall if it is supposed to be (can't recall what the pilot looked like last year). I did notice that there is a thin coating of soot on the burner tubes which I had not noticed during operation last year, so I assume the shutter needs to be opened more.

So my question is... on the assembly in the pic, is the center part of pilot supposed to engulf the flame sensor loop? If so, what would cause the pilot to not reach (assuming no change in gas pressure from last year). If it is not supposed to engulf the loop, could the soot have caused a pilot hood or flame sensor issue? Is it easiest just to replace the entire assembly or just the flame sensor? After only one year of operation, I should not have to replace anything!

FP1303_1_1024x.jpg
 

DAKSY

Full Time RVer
Staff member
Dec 2, 2008
9,079
Wherever we're parked
I would say the rectification rod (Flame Sensor)
should be completely engulfed in the pilot flame.
Your owner's manual will confirm that.
What fuel are you burning? LP or NG?
Both fuels contain small amounts of moisture & can cause rust to form in Black Iron Pipe,
if that's what is used in your home. Small pieces of rust can break loose & travel to the
pilot hood, causing partial or even total blockage of the pilot flame.
Compressed air can be useful in clearing the debris.
 
  • Like
Reactions: clancey

jtech1

Member
Nov 2, 2014
22
US
Thanks, I'll try compressed air both ways in the pilot tube.
If inlet pressure is proper (I have a pressure test kit so I know the inlet pressure is in range), and I blow out the pilot line, and still flame does not reach flame sensor, anything else to check, or time to call a service tech?
 

jtech1

Member
Nov 2, 2014
22
US
My inlet pressure is perfect at 7". I removed the pilot line from the gas valve and use air pump to blow out the line. Some dust came out but nothing major. Flame is a little better, but not much. Every now and then the pilot flame from the center of the 3 ports on the pilot hood does reach the flame sensor and the spark stops for a while. If I light the burner at this point it will stay lit, since the burner flame also keeps the flame sensor engulfed. But with only pilot lit, the pilot flame will not always stay on the flame sensor. It will then start sparking again, and eventually lock out. The center port flame from the hood seems like it is bending up toward the top port more than coming straight out at the flame sensor. I have attached a picture. You can see the sensor loop just to the left of the flame, and the center port flame bending up ward. Could this be caused by the flue draft or most likely still a pilot hood issue/weak pilot flame and needs replacing?

IMG_4276.jpg
 

DAKSY

Full Time RVer
Staff member
Dec 2, 2008
9,079
Wherever we're parked
It could be the positioning of the pilot hood. Can you 'tweak' it downward a little with a pair of needlenose?
 
Last edited:

jtech1

Member
Nov 2, 2014
22
US
I decided to just replace the entire pilot assembly... worked perfectly. Mendota does not make it easy to change the pilot assemble and seal it properly... had to take out the burners and the metal shelf they sit on to get access to do it properly... so did a full clean-out while I was in there.

There was some soot on the burner tubes. I am going to use the front panel shutter knob to open the rear burner shutter a bit more. The manual says the front burner shutter on the tube itself is preset at 1/8" and should not need to be changed. Is it likely all the soot is from the rear burner, or should I adjust the front slightly more open also? UPDATE: After looking at things a little closer, I am questioning whether this is soot on the burner tubes... it looks like on the parts of the tubes without holes, there is a black coating... and I am thinking that what rubs off like soot may just be the black coating burnt off. I do not see any soot buildup anywhere else on logs or glass...

This unit sat in my garage for 5 years before I installed it a year ago... and it was only run last winter. But the pilot assembly had some rust on it. I also saw some rust in the rear air intake. Any idea what this would have been from? Is it just from moisture in incoming air? If so, does leaving the pilot on all year help prevent this?

IMG_4347.jpg
 
Last edited:

DAKSY

Full Time RVer
Staff member
Dec 2, 2008
9,079
Wherever we're parked
Keeping the pilot on will help to mitigate rusting, but the problem comes from the actual burning of the fuel.
The environment within the firebox is pretty harsh & when the paint peels off, the bare metal will rust easily.
Incoming air during damp weather will add to the rust. It's a good idea to tune these units up every other year,
& that should include a thorough cleaning, wire brushing & painting the firebox.