Ongoing Furnace Problems - Part 8,977
All: Here's what's been happening thus far.
The techs replaced the supply ducts with larger supply ducts, replaced the return ducts with larger return ducts, added a return duct going to the second floor, added a by-pass damper, replaced the inducer motor and pressure switch.
The blower (fan) still continues to run after the heat cycle ends, and doesn't stop running until the next heating cycle when the furnace does its start-up routine. This doesn't happen all the time.
In the beginning the problem was related to the limit switch stuck in the open position. Then it became the pressure switch stuck in the open position. I checked the fault indicator light on the control board last night, and it showed that the limit switch was stuck in the open position. I manually cycled it by rapidly switching the power switch off and then on. As of 5am this morning it was working fine.
I notified the tech people who did the work (rightly or wrongly) that I believed that they did what they felt was necessary in order to address the problem, but that the problem still persists. I believe that the furnace at this point probably needs to be replaced, given that the techs have essentially been rebuilding my hvac unit. I don't believe that it's their problem...I believe that I just got stuck with a lemon, and it's time to cut my losses by either replacing the furnace or by ignoring the continuously running fan as long as everything else seems to be operating normally. Note that the hvac unit was installed when the house was built in 2000.
This unit is a high efficiency unit, 90+ AFUE. It's been a problem since day 1. You guys/gals on this message board have attributed part, if not all, of the problem to the fact that I have one furnace, one central a/c unit, and two zones using a motorized damper system. Perhaps you're right.
If the fan continues to run, and everything else appears to be functioning normally, is there really a problem? I've read that a continuously running fan actually contributes to a more uniform temperature throughout the house. The continuously running fan cycles off when the next heat cycle begins. The only nuisance is that at the end of the heating season, when we get those balmy days with cold mornings and warm afternoons, the fan may not shut off, and I'll have to shut is off manually.
Just thought you'd like to know...and if you didn't want to know, I apologize.
Find The Problem!
You shouldnt have to replace the furnace because the fan continues to run! Hell the unit is only 7 years old. There isnt a whole lot that can go wrong with them that would constitute replacing the unit!
If a qualified tech cannot find why the fan continues to run than dont pay him and call another tech out.
Usually if the fan continues to run it is usually caused by a saftey that has tripped. Is there a LED indicator light that flashes on the circuit board? If so the code will tell you what it tripped on or give you a good idea on what it tripped on.
If the unit is a zoned system there usually is dip swithces on the circuit board that maybe in the wrong position and causing it to run.
I do not know the history of the unit so I am just thinking out loud.
Find the Problem
Mr. FSH: The tech did find the problem, or so we thought. He said that the problem was caused by the limit switch tripping, which was caused by undersized ducts and absence of a by-pass zone. We went along with his recommendation to enlarge the supply and return ducts, extend the return duct, etc., etc., etc. After the work was done, the limit switch kept tripping, so the tech adjusted the by-pass damper. While he was testing the system the pressure switch tripped. He checked the inducer and determined that the inducer and pressure switch should be replaced. That was done (under the service contract for free). The parts were replaced yesterday, and last night something tripped that caused the fan to continue to run. I checked the indicator light on the control board, and it showed that the limit switch was stuck in the open position. I flicked the power swith off and on, which reset the limit switch, and it tripped one more time last night. As of this morning, everything seemed to be working fine.
The problem with the fan continuing to run doesn't happen all the time, and it may not happen every day. One of the by-products of the larger ductwork is that the system runs quieter, so the constant running of the fan, as a practical matter, is more of a nuisance. The only time I know that there's a problem is when neither zone is calling for heat and the fan has been running for several minutes and is blowing cold air.
I am not a hvac person, and I have no technical knowledge. Based on the little bit of research that I've done, and the postings I've read on this board, I believe that maybe the flame on the burners is too high and has to be adjusted. Everything else has been tweaked, adjusted, replaced or repaired in some way, shape or form.
Thanks again for your input.
How did they install a Bypass damper?
They installed it coming off the main part of the furnace (I don't know the technical name for it). It dumps the excess air into the basement.
Originally Posted by second opinion