I've never seen that before. Is the inducer possibly not getting up to speed until after that 30seconds and not pulling the flame in?
I ran into a problem with a H9mpd075 furnace today that has me stumped. The burners ignite inside the burner tubes about .75 inches in front of the orifices, they burn there for about 30 seconds before jumping to the front of the burners where they belong. Furnace is on propane with an inlet pr. of 12 iwc, manifold pr 10 iwc. No adjustment of the manifold pr had any effect (tried from 6 iwc to 11 iwc). Anyone run into this before?
I've never seen that before. Is the inducer possibly not getting up to speed until after that 30seconds and not pulling the flame in?
Very interesting. I had a furnace that wanted me to cut out some metal on the intake ports. this was in the manual.
Have you tried unhooking the intake pipe or taking the burner box cover off to see if this would make it ignite properly?
Maybe you have some cold fuel? Does the furnace have a drip leg piped into it?
Has a new inducer assy. and the pr switch closes no problem.
was the proper orifice used on the new inducer if it has one?
I have seen pressure switches close when there wasn't enough pressure or not open when it became clogged with water. Have you verified pressure with a manometer?
i have seen this but not all the burners. does it make a whistling noise? or any noise? did you see any soot when you changed the inducer? a semi plugged hx will do this. also i have seen it stop after a cleaning.
The inducer for this furnace has the proper size inlet for the model. I checked to be sure the correct inducer was installed because each BTU size requires a specific inducer. Checked the burner orifice size, #55 correct for our altitude, there is a dripleg on the gas line, I disconected the combustion air pipe, no change.
How many burners are effected?
Are there any air shutters on the burners? Some models they want you to put a screw in each burner. Have you verified all the steps have been followed with the conversion?
Have you put a manometer on the gas valve to see how it's opening. Maybe the valve is hanging up when it opens. This furnace does have the dumbvalve, correct?
How old is the furnace?
Put a combustion analyzer on it. I'm sure the furnace will tell you something then.
Could there be a spider web in the manifold? I've seen some weird burner action (but just on individual burners) that had a spider web.
I would check the draft, too. I've had some improper venting make burners do odd things.
+1 for the combustion analyzer suggestion.
I'm eager to hear what you find.
Thanks for all your suggestions. So far the only thing I haven't tried is the combustion analyser, didn't have it in the van. Yes it does have the dumb valve, I hate those things. I'v replaced over 500 since they came out, and have seen them do some pretty strange things but never this. I watched the manifold pr when the valve opened and there was no fluctuation, steady 10 iwc from start till the flame jumped to its proper place. i'v pulled the orifices to check for blockage. I pulled the instructions for the propane kit and there is no mention of installing screws in the venturi and I have installed over 100 of the kits with no problems on any other furnace. Well I guess I'll beat my head against this wall tomarrow. Again thanks.
i would be looking real hard at the new bad inducer/wheel or secondary h/x
Is the draft steady? Check with a manometer or draft gauge of your choice and post the readings.
Someone else raised the question of a plugged heat exchanger but I would expect that would be a continuous problem rather than an intermittent one.
I just converted a new ICP furnace to LP yesterday. It was the first time I had to put screws in the burners as directed in the instructions. It was a new model and a new style conversion kit. The conversion went smoothly though.
Could the manifold be cocked, or twisted, not allowing the orifices to point straight into the burners? Just a thought, let us know what you find!
You were vague in your description of the series of events. Did you arrive at the house for a no heat call and find a bad inducer motor, and then have the burner issue, or was the burner issue present before you replaced the inducer? Also, check the colector box, as ive found three of these cracked in the past. I would install mixing screws in the burner venturi anyways to see if it changes anything.
You are right I should have started at the begining. The inducer had been installed by another service tech (who is no longer doing service work), about a month before I was called. This was replaced the homeowner said because the old one seized. His call to me was because the furnace started making what he called a ratteling noise. When I tried the furnace I found the problem with the flame burning inside the venturi of the burners, this caused the door on the front of the burner compartment to vibrate until the flame jumped to front of the burners. Upon inspection I found 3 cracks in the collector box (Hiel calls it the transition assy), I sealed those with hi-temp RTV silicone with no change in the flame at startup. I ordered a new trans. assy and installed it, and checked the tubes of the secondary heat exchanger at that time, (all were clear). That brings me back to the points in my original post.
Have you checked the pressure in the combustion box? I remembered I had a similar issue on a mobile home furnace with a combustion air restriction.