Delayed ignition, can't locate cause

[NHJim]

Hi all,

I have been struggling with this gas stove issue for a month and can't seem to find the cause. I am hoping you have some pointers or advice for me!

I have a lennox country stoves vintage 27 gas stove running LP gas. Basically, when the thermostat kicks in, only a very small segment of the burner initially lights up, about 2 inches out from the pilot light. Then I wait from 20 seconds to up to 10 minutes for the rest of the burner to eventually light. The longer I wait, generally the stronger the boom when it finally lights.

The burner is clean, the logs are installed properly, pilot is working, I have had a technician in to check the pilot, gas pressure, all the usual and they are telling me the next step is to order a new gas valve ($450 part). Before taking that step, I wanted to ensure that was the likely problem.

See this 1 minute video of the stove lighting for the exact behavior. You will see the thermostat kick-in about 5 seconds in to the video, with just small segment of the burner lighting up. Then wait.... Eventually boom the whole burner lights. Is the gas valve messed up? gently tapping on the gas valve while waiting for the stove to fully ignite does NOT cause it to finish the ignition.

(broken link removed to https://s3.amazonaws.com/hut-stove/VID_20180311_092026.mp4)

Thank you
Jim

 

[DAKSY]

Is the gas line clean behind the burner orifice?
Is the burner aligned correctly on that orifice?
The problem with LP is that it's heavier than air & it "puddles" in the lower part of the burner area, if it doesn't ignite immediately...
This allows it to build up until it reaches the pilot flame at which time the entire amount in the area ignites at once.
What was reading on the "Manifold Pressure" that the tech obtained?
Did the tech try adding another hole in the burner directly adjacent to the pilot flame to allow more gas flow for burner ignition?

 

[Tech Guru]

I'm with DAKSY on this, verify the manifold pressure. There does seem to be a gap in the porting between the area that lights off immediately and the rest of the front burner. Is that there by design, or is there a port that has been blocked or obscured in some way?

 

[NHJim]

Hi, thank you both for your reply.

Let me respond as best I can:

I believe the gas line is clean and aligned properly. One reason I believe this is that the delayed ignition is not 100% repeatable, sometimes, particularly when the stove is cold, it fires up normally. Other times it takes 20 seconds to fully light, other times you have to wait 10 minutes. I fully cleaned the interior as did the tech, and verified each hole in the burner was clear and clean. They were not dirty or blocked. The tech said he measured the pressure which was "perfect" but I do not know the specific result.

You are right, in the burner design, there is a small space between the section that lights up immediately and the remainder of the burner. This is by design, there is no blocked hole there. However it is like there is a hole missing. But absolutely there is no hole in the burner and the small gap is by design for some reason.

Also this stove is about 12 years old, it has run flawlessly for many years with occasional cleaning, maintenance, until this issue developed this season. It would seem odd to add an additional hole in the stove burner at this point when it seems something is just faulty.

The only other thing I will report, as you see in the video, when the thermostat kicks in, the small burner section lights up immediately and reliably every time. It is the rest of the burner that experiences this delayed ignition. A few times, while waiting for the full burner to light, I have manipulated the flame strength knob on the valve controller, or the on/off/pilot control, and the burner has immediately fully ignited. Other times, I manipulate the knobs and nothing happens.

The above observations had let the tech to conclude that the gas valve may be faulty or sticky. However, this tech is a general gas/furnace guy and not a gas stove expert. Maybe I need to seek a stove expert at this point?

Any other observations or recommendations for me?

Thank you again

 

[DAKSY]

OK. Did the tech remove the burner ORIFICE?
Did he run a pipe cleaner or a Q-tip type swab into the gas line BEHIND that orifice?
When the ON switch is actuated, can you HEAR a "CLICK?"
If so, the electromagnets have opened & the gas has begun to flow.
Looks to me like not ENOUGH gas is getting to the burner, as is
evidenced by the anemic flame in the first couple of inches.
Once it builds up in the gas line, there's a SURGE of fuel coming out & igniting.
My bet is a spider's nest in the gas line, BEHIND the burner orifice,
& the build up of pressure is finally pushing the nest out of the way of the fuel flow.

 

[NHJim]

That is a very interesting idea, thank you DAKSY.
When the thermostat kicks in, I do hear a click.
Sounds like next step is remove the orifice and very that all is clear.
Thank you
Jim

 

[DAKSY]

Keep us in the loop!

 

[NHJim]

Well, stove seems to be up and running.
Gas stove expert came in and found some rust/corrosion inside the burner holes, looked clean from the outside but was apparently slightly interfering with flame. Drill bit seems to do the needed work. Also added glowing embers along the burner. The result is the flame is now 'jumping' that seemingly missing hole successfully and ignition is back to normal it seems.
Thanks for your inputs, and saving me from replacing the gas valve which clearly was not the issue.
Good forum thank you!
Jim

 

[DAKSY]

Glad you fixed it WITHOUT having to replace the valve.
They don't fail very often...