York Furnace/ Pilot Problem

[svc]

I have 4 yrs in the trade and I've got a stumper.

York model#p-hed12n04001a serial# eeapo11342
horizontal gas furnace

It has an intermittent pilot problem and locks itself out. The pilot light flame flickers the majority of the time like your trying to blow it out and then will suddenly stand normal and all systems are go!(main lights).

I have checked the following :
orifice is clear
sensor probe has been lightly sanded
24v at pv to comm
ignitor sparks at all times during trial
7 in w.c. to pilot tube
no obstructions in flue piping
draft motor is working correctly and in the right direction

I have installed new gas valve sensor wire and ignition module and I am getting the same results please help me with this nightmare! thanks

[key]

change the gas valve, you have got a restriction inside (pipe dope or factory), I only make my final connections to the valve with approved teflon tape for this reason. You might also try blowing out pilot tube with nitrogen before replacing valve

[Edited by key on 04-06-2005 at 07:51 AM]

[dapper]

Time Out!!!..... You say 7" on the pilot tube? That is way too high. Check the factory specs but I think that should be around 3.5" to 4". That's why the flame 'flickers' all over.

[chill factor]

Im with dapper. 7"wc sounds way too high. You didnt mention what the flame signal was. Also your flame sensor should not have more than 2 ohms resistance. If it does replace it.

[ac/dc]

I respectfully disagree Dapper, Pilot pressure is usually
same as inlet gas pressure. Ive seen lockout prblems on york packages due to low pilot pres 5.5 w.c. I remember
those old furnaces where the pilot valve was seperate and on the main gas line before the main valve.

SRV you didnt list the micro amp signal. You cleaned the flame sensor but what about the pilot shield and other
chassis surfaces at the pilot.Is the ground tight from ign
control to chassis? An unstable or abnormal pilot would
cause poor or failed flame sensing. I agree it could be the
gas valve.

[service guy]

SVC where are you taking the pilot pressure from are you taking in line or are you disconnecting pilot tube and checking at gas valve? If you can take pilot pressure in line so you can get a reading with pilot lite I find this is more precise.

[ac/dc]

Service guy, what pilot pressures do you typically see
with inline measurment while the pilot is lit?
On this gas furnace the pilot pres regulator within the gas
valve may be at fault. I would expect to see 5 to 7 w.c.
at the valve but I have never checked it with the pilot lit. Just curious

[brettln]

Sometimes the gas valve itself will stick.
You should have 7" w.c into your regulator and aprox.
3"-4" coming out of your gas valve. You should still get the same reading with pilot lit and running.
7" w.c. after your valve is too much. Also just for special note* If it's a universal gas valve make sure it is set up correctly....nat.gas or L.P.

I acually had a gas valve not fully seat, and was allowing
gas to spew out. Call was for strong gas odor in hallway.

Hopefully that helps......maybe / maybe not

[ac/dc]

Actually your right if your talking about the main burner.
The pilot burner has a seperate regulator (which doesnt
work half the time) in the valve and if you check the pres
where pilot tube connects to gas valve it is generally 6 - 7 in w.c. The pilot orafice is sized for this pressure.

[service guy]

ac/dc I like to see 3.5 to 4 wc I may get 7" at valve but this would simply be static rather then running pressure i want to see the pressure as the pilot is lighting of and after it's lite.

[ac/dc]

OK Ill buy that, Ive never checked it that way but it makes
sense. Maybe next time (if there is a next time) Ill check
it that way and see.

[flangehead]

Better check the micro amp signal on the pilot

[observation]

7 inches on the pilot tube sounds way to high check manufactures recommended manifold pressures.

[bob the head scratcher]

Heat exchanger ok?