This is just a layperson's opinion.
The basic hardware componets are almost as reliable as they ever were.
The gottchas are:
The flame igniter and the control board. Both of which are very costly if
you have to pay a service company to replace them.
There is also the draft inducer blower which I have not replaced yet.
A $15 igniter can cost up to $150 with a service call and off the truck
The control boards run $200 and up plus labor.
I have replaced 2 igniters and one control board in 10 years (two furnaces).
IMO the cost of the gas for a 70% system would have been less.
HVAC guys don't flame me I just told it like it is.
There is nothing here to flame you on. You did indeed tell it like it is.
In fact, if the only difference between two new systems is the ECM v PSC
blower motor, I recommend the lower SEER of the two.
My 20-year-old Carrier SX had it's inducer motor bind up due to
condensate running into the bront bearing. I replaced the motor and
blower wheel with aftermarket parts, and added a slinger ring to keep
the water out of the bearing. That one lasted about 4 years, and when
I opened it, and found that the blower wheel had disintegrated from
I reinstalled the original galvanized wheel, and it's been running
ever since. The only other difficulty I havd is a codensate leak
from a joint in the exhause plenum, I disassembled it,. cleaned and
re-sealed, and have had no further problems. No igniter problems so
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Of course, you could have replaced it with a regular pilot light the
first time the igniter went, correct? I turn my regular pilot light
off in April and light it up again in October. Saves gas and is
Not on alot of the new stuff, no ignitor signal and no gas valve open...why
would you want to throw out $500 in parts for a standing pilot when the fact
is that you can replace the crappy ignitor with a ceramic one that will
probably be the last one you ever need to put in the unit?
I have igitors that you can about drive over and still work.
Not that you would WANT to, but still...
To answer the OPs question:
Till it breaks.
Now long should you service it? EVERY YEAR, without fail.
From a pros, not even close.
Several makes of furnace, have incredible failure rates on control
boards...Lennox, being perhaps the worst.
Theres no such thing now as a $15 ignitor...those are now $22-$25 wholesale
and I dont use the cheap things.
The ceramic ones I replace the carbides with are now in the $45 range
wholesale, and I have never replaced one for more than $100...
Most we replace are under $200 with labor...
SOME, can be VERY high, and normally, the older the unit, the more expensive
There are exceptions, and have seen a few that are in the $450 range
Not flaming you, but might I suggest that in some areas, such as mine, its
illegal to sell to a non licenced person, therefore, you are at the mercy of
the company that is doing your service and repair work.
While that can be a good thing, overall, when looking at the big picture, it
can also be quite a hindrance to someone that is looking to repair his own
unit, that isnt qualified to work on it, and has no clue about the proper
installation or testing once the units repaired.
I might also add, that there are indeed times, that just replacing a part,
isnt the fix that the unit needed, and you may have many people that can
tell you that XYZ company came out after they replaced a part several times
themselves, and finally, when they could not figure out why it continues to
fail, they call XYZ and they in turn, found another part that was causing
the secondary part to fail, and since they repaired it, it hasnt given a
Somehow, the IDIOTS (caps intended) with one of the local phone books got my
company listed as a supplier instead of a contractor. That's been good and
bad. Getting on witht he story, though, I was called by a customer that was
looking for a 'relay' for their outside unit(actually, they were looking for
a contactor). I explained that I wasn't a supplier, I operated a service
company. I also told them since I was in the area, I'd come by and look at
the problem. It wasn't the contactor, it was a loose wire in the furnace.
Ya gotta know what to look for....
Now, Im also a supplier. Source One to be exact. however, its rare that a
homeowner calls and asks for parts, altho it happens.
When they do, I hve to ask what company they are with. If they are NOT with
a licenced AC or heating company here, I tend to shy from selling to them
now after a couple of fiascos last winter that got nasty. Had a guy call
about a board that kept popping on him, and for some reason, the fuse never
popped. I KNEW it had to be in his wiring, but he refused to allow anyone to
go look at it, so I replaced two boards under warranty, and told him on the
3rd one, no more. PERIOD.
Found out later why he didnt want anyone to go look at his unit. When I ran
the numbers on it to see if it was still under any warranty, it came back as
still sitting in a warehouse......when I called them to see if they had it
on file, they did, and I said, go find it....cause Im looking at it...
Whaddya do? Call the local PD on Nextel and deal with it as you can..illegal
is illegal, but why are the crooks the stupid ones?
Oh..his issue was that he had one wire, going to the cap on that FRP unit
under the rubber cap protector, that had come loose and gone to ground...
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