I get my 25 yr old oil & hot air furnace serviced every other year.

Last fall there was a new kid at the place where I've had this done
for 20 yrs & I watched him tune it up. He actually seemed to be
doing a more thorough job than his more experienced predecessors.
He was the first one in years to open the plenum & vacuum the top of
the heat tubes.

But he didn't do the ?CO2? test-- where a probe is placed in the
stack. I asked him about it & he passed it off with a 'we don't do
that any more'. The old guy that was 'watching' him didn't disagree.

He left & for a couple weeks the furnace seemed fine--- but then it
started this random 'stuttering'. [or I started noticing it] Maybe
once every 10th [or 20th] cycle you can hear the furnace start-- then
stop-- then start - sometimes as many as 5-6 times. The next cycle
is always perfect. I've spent hours sitting beside this thing to try
to figure out exactly what is happening, but I've never caught it
actually acting up. The blower fan works steady through this
stuttering so I've ruled out an open in the electrical feed. If I
remember correctly the photocell will trip the reset button after the
second try. So far it hasn't tripped the reset button at all. [ I
'tested' the reset button this fall when I changed the filter & forgot
to bleed the line-- that tripped it.]

Another random and discomforting problem is some exhaust smell on rare
occasions. I think I did catch this one once-- The burner fired &
though it sounded good, there was a lot of smoke & it was coming out
of an old probe hole in the stack-- and around the damper in the
chimney.

This fall I finally decided to pull the nozzle & look at the ignitors.
I was sure I'd found the problem as the ignitors were set to fire
exactly even with the nozzle head. [.75, 80degree hollow cone] I
re-set them to 1/8" ahead of the face of the nozzle, 1/8 apart & 1/4
above the hole. That seemed to do the trick-- but I've heard it
'stuttering' a couple times since.

I don't get any of the pre or post combustion 'pops' that would
indicate unburned fuel being left in the plenum. I do smell burned
fuel outside sometimes if the wind is just right. I don't know if
this is just when the furnace is doing its 'stuttering' thing- but it
is also random. I've never seen any smoke coming from the chimney.


This is a one line system & the *new* tank is outside and about 5 feet
higher than the furnace. Filters were replaced this fall & there was
no sign of gunk or water in either one. [I have 2 inline filters
because I had an old tank under the eaves & I added a filter in the
low spot of the line to catch water.]

Any thoughts on what might be causing the intermittent 'stuttering' of
the burner?

Jim