Ok, now that my furnace was scrubbed and cleaned and a new thermo
coupler for the pilot ignition was installed, I got a new filter to
install. However, as I pushed the filter into the slot, I accidentally
brushed/hit one of the wires on the blower and the flames died out and
only the pilot light remained. I replaced the blower lid and the
burner door, went upstaris to make coffee, and went downstairs to hear
that the furnace was burning full blast . I opened the burner door
to look inside, and the flames were burning birghtly, then they died
out and only the pilot light was on.
I don't remember this ever happening before. The flames were always
burning brightly and never went to pilot status when I had opened the
door previously. Now that the burners are cleaned and scrubbed, and
all the scale and rust has been vacuumed out of the furnace, is the
above normal operating procedure?
Yes, that most likely is normal operation. There is usually a door switch
that turns the unit off and on. Obviously I can't see it from here, but you
can...look for some type of push switch that the door come in contact with
around the edges of the cabinet.
More like a vertical lid that slides off with great difficulty. With
the burner door on and the blower door/lid in, the cycle is 1) pilot
light 2) full burn 3)blower on 4) blower off with full burn 5) pilot
light. Basing this on sound since everything is closed. I didn't
notice any switch where the blower door lid would come int contact
with. I wonder if the brand new thermal coupler is responsible for
I checked again, still no blower door switch. Must be over 30 years
old. Brushing the filter against the wire and the pilot light only
coming on was probably a coincidence. The tech had also replaced one
other part, no charge. Don't know what it is called, but it is some
king of big sliding nut that is connected to a thick silver rod that
is next to the pilot knob.
The actual sequence of events is 1)pilot 2)full flames) 3)blower with
full flames 4) blower off with full flames 5) pilot light 6) pilot
light with blower.......(I guess this is good since there is still
enough heat in the furnace to trigger another blast from the blower
even though just the pilot light is on. Getting 2 blasts from the
blower for the price of one cycle of gas, although the second blast is
much quicker in duration.) 7)pilot light without blower. Repeat
When the tech was here and started the burner with the blower door
off, full flames came on after he lit the pilot light and turned the
knob to on, and the flames continued like that and didn't go back to
pilot. Blower worked normally. Maybe it was the thermostat constantly
calling for heat....the inside temp was around 55 and the thermostat
was set at 70. With all that cleaning, maybe the thermostat now works
properly and now that the internal temp now matches the thermostat at
65, it goes through the cycle as described above, and uses much less
gas. In the past, always seemed that the burner was constantly on full
blast. Thinking out loud.
Also, the thermostat is off by 5-7 degrees, but it's thermometer is
accurate. I have to set it at 60 in order to get 65-67 ,etc. I should
probably get a new one. An analog, presumably 2 wire, Honeywell is the
brand I got. Any recommendations?
Also just noticed that the blower motor area wasn't vacuumed. Slight
oversight to a thouroughly excellent job.
Sounds like a pilot tube...but you know...no one can see it from here...and
you have yet to give any real information...like..brand of unit, model,
serial...cause if you had, not only could we tell how old it was, we could
tell you what SHOULD be on it.
That is wrong. And its costing you.
IT could be from improper heat rise, caused by improper burn set, it could
be from an improperly set fan switch, or a bad fan switch...
The second blower run is wrong, and its not a good thing....
I dont know....we bypass the blower door switch while working on units,
since there are times you need to have things open to properly check
items...like blower fan RPM and such with the tach..
The thermostat is nothing but an on, and off switch...it knows NOTHING about
how the furnace is running, or the sequence of operation of the furnace.
You keep talking like you have a two stage burn furnace, and I can guarantee
IF you do, you have a blower door switch on it.....since they havent been
Is it a T87..the round one? If so, level it. If its not, check level on it.
Your furnace guy should have done this as well....
Sounds like he took your money and you feel good about it.
How long was he there? 20 minutes? 30? Average time for a gas unit to be
properly serviced is over an hour. It takes about 10 to 15 minutes just to
check the WC on the manifold and line. Then you have your leak tests and
checks, and then the heat exchanger inspection....(and from the sound of
your double run on fan, you really needed that..seriously) then there is the
spillage check, the CO test, the cleaning, the adjustments, the heat rise
check and adjustment, blower cleaning, HE cleaning, thermocouple
replacement, thermostat calibration, and level if needed, terminal checks,
ductwork checks flue check.....and thats on an older unit...there are still
all the roll outs to be checked for operation, proper sequencer operation,
door and flue switches, inducer motors on the newer units, gaskets and seals
to be checked.......the list go on...
We charge over $175 for that...what did you pay? $35, $50? $100 even?
Sorry to say, sounds like you got what we call a hit and run....if you have
a legitimate contractor, he should be willing to return and check your
thermostat free of charge....if not...well..you get what you pay for most of
Any furnace company that claims a check can be had for $50 is actually not
lying....they check to see if you HAVE a furnace..and thats about it.
What is the proper sequence ? I assume from the above that the furnace
should be fully burning at all times and I should not see only the
pilot light at any point.
Is the second blower run dangerous?
First guy I called didn't even clean or change anything. He was
pushing hard to install a 5000 dollar furnace. He claimed it would
take 5 hours to remove the burners. The second guy took an hour to
take out the burners and scrub and clean them and check the limit ,
replace the thermo couple. Unfortunately, he didn't check the blower.
Probably becaue at the time it was working properly , the pilot light
did not come on just by itself. The furnace was burning fully.
You have to understand, I am completely new at this so every
experience I am learning more and learning more from the responses I
get . The second guy was a big improvement over the first. At least
the second guy got the furnace working and the auto setting on the
limit to work. BUt not good enough according to you. First guy was 140
bucks for pretty much showing up, and the seond guy charged 186 for
labor and one part for an hour. Maybe the third time will be the
charm. Is there a checklist for things I should ask for? Your industry
is full of crooks so it seems.
Proper burn..standing pilot furnace:
Thermostat calls for heat
Gas valve thermocouple detects pilot flame, (constant, since the
thermocouple generates a tiny voltage amount) and opens allowing burners to
light, or fire...
Heat exchanger warms air around it, causing fan limit switch to start climb
towards fan start
At around no more than 150F air temp at fan limit, fan switch turns on
home is heated
Thermostat is satisfied, ends call for heat
Gas valve shuts
Blower runs until fan limit switch cools to shut of temp, set on dial.
Unit sits with pilot lit until next call for heat.
Not unless you have a cracked heat exchanger that is allowing the fan limit
switch to become overheated.
Five grand for a furnace....damn...I am not charging enough....
The industry IS full of crooks, as is every one. By the same token, Usenet
is not always where you will find the right answer to every issue..:)
No, your service was NOT good enough, or else you would not be having what
we call a run on condition. While it MIGHT be a simple adjustment to the fan
limit, I would be more concerned with the heat rise, and if its too high. If
it is, due to your previous techs failure to check it after cleaning the
unit, the blower will continue to cycle as it is until the burn is corrected
and the heat rise is lowered.
hell, if you are in my area, (central NC) Ill come by and check it for you
and if its an adjustment, fix it for a hell of a lot less than they did...no
Educated consumers, help us that are legit, and trying to do the right thing
for everyone, run the bad guys out. i dont mind charging what I do...most
people agree, they will pay more for competent and correct service, than for
half assed hack work that costs more in the long term than in the short.
Good luck there.
Ok, I had thought when you stated heat rise, you meant the heat didn't
rise up through the flue and ducts. SOunds like you mean the heat has
risen too much in the furnace , thus the second blower run when the
burner is off as a result of too much heat still inside. The first
blower run didn't force enough hot air through the ducts?
Can the heat rise be a problem of the limit switch setting? The tech
showed me that the limit was set between 100 and 150 with emergency
shut off at 210. However, I just read on the furnace that the switch
is supposed to be set at 70 and 100, unless I misread what was
SO you are saying that the second blower run could correct itself
Thanks again for all the helpful responses
70 and 100 is too low. 100 and 150 is apparently too high. I would
take it to 90 and 140. If that doesn't take care of the double run, I
would go to 80 and 140.
The proper setting varies from system to system. Also, its entirely
possible that the fan switch just doesn't hold its settings anymore
and needs to be replaced.
Gary R. Lloyd CMS
HVACR Troubleshooting Books/Software
This is Turtle.
I would not be so quick to call a third company out when you have not called the
second guy back and explained the problem. If you called me back and said it was
still not working properly. I would come back for NOTHING to see about it. Call
him back and see what happens .
Now watch out here lumbing the second guy with the crooks out there. I have
cleaned a burn and replace the thermocouple and see nothing wrong with it and
leave and get called back to a Fan / Limit switch start to acting up . A fan /
Limit can work good one minute and when you leave it will start screwing up.
This is Turtle.
I think your lumping in the second guy who worked on it in the crook area when
he did what he come to do and not spend another 1 to 6 hours checking the
complete system out from one end to the other. The customer called him to come
fix it and not give him a complete system check out which would take atleast
another 3 hours at $70.00 a hour. $187.00 for the fix and a another $210.00 to
check the whole system out. = Just short of $400.00. Just reading here.
Holy mother of God...that things still running?
Good going...seriously. I worked on many a Pentastar...tanks...absoulute
Make DAMN sure someone runs a CO check on that unit....90% of the
replacements we have done on those are due to cracks in the exchangers. They
are good units for the age, but like everything else, they will fail over
Not trying to sell you anything, but in all seriousness, they also are fuel
hogs...a new 95% unit will about pay for itself in very short order in
savings compared to that one...but 5 grands a bit steep, altho I cant see it
from here but I assume its in a location thats not hard to get to.
This is Turtle.
Look on the top part of the blower door and you will see a push button switch
that will be pushed in when you put the blower door back on and will release the
push button switch when you open the door. The switch was problem stuck over the
years and the fellow cleaned all the trash out ans a service man will clean and
pop the switches to make sure the will pop out when the blower door is removed.
This push button switch will kill all the 120 volt power to the furnce when it
is released. When it pops out, the burners and all blower motors will stop and
only the pilot lite will keep burning.
Now you do know your suppose to turn the furnace off before opening the blower
door because you can in some cases pull the flames out of the burner area and
out to burn the wires if the blower motor is running with the blower door off
while running the burners. This is what the switch is on there for.
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