Another weird electric (furnace) problem
I stopped by one of my favorite customers the other day just to say hi.
Elderly couple in their seventies I’m guessing, but both sharp as a tack.
They have a gas forced air furnace that is only a few years old. Looks like a high efficiency unit. No pilot light.
This past early spring, the furnace worked fine during the day, but in the middle of the night it didn’t work. The guy would get up to use the bathroom and he could hear it trying to kick on, but it wouldn’t succeed and after a bit would stop. Then it would try again after a few seconds.
But when he turned on the light over the table in the kitchen, the furnace came on and worked, no problem.
Again, during the day it worked whether the light was on or not.
The AC works fine twenty four/seven.
He had the installer out and he seemed to feel that it might have something to do with the hospital (1/2 block away)…that maybe the hospital was pulling more load in the middle of the night when rates are lower.
The installer also said that he felt there would not be a problem if the furnace had a pilot light.
Any thoughts I can pass on to my customer??
Thanks.
Rich Beckman
Coming to the Fest? Don’t forget pencils!!!!!!!!!!!!!
Replies
Sounds like it might be another bad neutral problem. Should have someone check the voltage on both sides of the 240V line in the middle of the night.
I'd look to see where the power came from for the furnace, as well as the damper. Chances are, the circuit is wired improperly, so it is being affected by another load.
The hospital down the block cannot possible be the cause.
A pilot light would avoid the problem ... most likely ... but would burn $10 of gas every month just to stay lit.
Another possibility is a bad control unit, or bad connection / wire from the unit.
A lot of the furnaces without standing pilot use a hot surface ignitor and a "flame sensor".
The flame sensor is just an insulated rod in the path of the flame. I don't know the full details, but it completes a circuit through the metal frame.
The furnace needs a good ground and correct polarity of the wiring for that to work correctly.
I don't say exactly what it is, but I suspect some kind of floating ground and/or neutral that changes when the light bathroom light is on.
And probably during the day other things are on that changes the conditions.
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Polarity is reversed at the furnace. Yes, it matters. Might even be a self diagnostic code flasher on the control board.
Other circuits could also be reversed and backfeeding somewhere. Start checking outlets with one of those plug in testers.
Could also be a bad ground connection. Intermittent ignition furnaces should have a ground wire from the panel.
I chatted with the customer briefly today. I mentioned that it might be helpful if they could nail down EXACTLY what was on and what was off when they went to bed so we might recreate the circumstance without having to be there at 2 am.He reminded me that we won't be able to recreate the circumstances until it is colder outside. The furnace worked in later spring when the lows were in the high fifties or above.The situation requires the outside temp to be below the neighborhood of fifty (or maybe 45)!!
Rich BeckmanComing to the Fest? Don't forget pencils!!!!!!!!!!!!!
That makes no sense.
There is nothing in the typical residential furnace that senses outdoor temperature.
Odds are, it is a ground problem- which will only manifest itself during a call for heat.
Either the grounding is poor on the 110v side, or there is a fault in the flame sensor circuit (essentially, a low voltage ground loop).
Local outdoor temperatures are likely a coincidence.
All bets are off if there are impropely wired accessories that sense outdoor temperature.
But loads on the local distribution network are highly dependent on temperature, I'd bet. Especially if someone has a flock of space heaters in their house.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Still doesn't make sense with grounding issues.
If a supply issue is suspected, will the power company provide a recording station to track brownouts?
They might -- worth asking.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
There are some other, far out possibilities. Hard to tell not being there and not know what kind of furnace it is.AFAIK all new furnaces have some type of electrical ignition instead of a standing pilot and that what is focused on.And even some of the basic ones have forced draft and the high efficient, condensing furnaces, all have some kind of forced air on the exhaust. They have have several kinds of safeties for verifying air flow and/or possitive air pressures.Some of those kind of things will lockout, other will keep trying, at least for a several cycles.And some reset with the thermostat. Other can be reset by cycling power.If the bathroom light automatically runs a bath fan that could be changing the air pressure in the house. Not sure what is going on during the day, but it might even just be chimmy effect from the sun heating the house.Also we really don't know that it works CORRECTLY during the day. It could be that 50% of the time it is still cycling. But it catches enough to run to keep the house up to temp. And with the normal noises during the day no one realizes it..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
It could be a squirrel that nests in the air intake and blocks it at night. Lots of weird stuff like that happens. I don't think it has to do with electrical problems.
"It could be a squirrel that nests in the air intake and blocks it at night."
That would be ironic. One of the guys pastimes is to keep a small live animal trap in the backyard to catch squirrels (they feed birds). Then he takes them to the large city park a mile or so away and releases them.He just recently started taking them to a cemetery that is maybe two miles away and across a very busy road.
Rich BeckmanComing to the Fest? Don't forget pencils!!!!!!!!!!!!!
Where is the thermostat and what type is it?
"Where is the thermostat and what type is it?"I'll have to check. I'll be there later in the coming week.
Rich BeckmanComing to the Fest? Don't forget pencils!!!!!!!!!!!!!
Rich,
These types of problems are impossible to troubleshoot with logic.
The correct method is straightforward, but tedious; Remake every connection, from the circuit breaker(s) out, recording voltages before and after, observing polarities, and generally eyeballing conditions as you go. Replace every nickle and dime part as you come to them. Set a limt of, say $14.95. If the electrical part costs less than the limit, replace it, even if there is no logical reason!
Replace every 50 cent fuse. Replace that $10 thermocouple. Replace that $5 switch. Observe polarity and record voltages.
If a significant change in polarity, ('cuz it was wrong) or voltage occurs after remaking a connection or replacing a part, stop and wait and see if the problem is fixed. You might do the whole system, never seeing any results, and find that the problem never again occurs?!?!?!?!!!!
Because this technique is not taught in schools and most techs don't have enough experience to have seen many "Gremlin" problems, the best way to get it done might be to contact the local trades school and contract with a student to "remake, replace, observe, record, and nothing else."
SamT
No emphasis added anywhere, 'cuz I don't wanna mess with HTML this early (|:>)
Edited 7/7/2007 11:34 am by SamT
I sorta of agree.But it is WAY TOO EARLY TO DO THAT.I have had too many times that I get the call after something is not working and they have tried the shot gun approach at fixing it.The problem is that at that point you don't if you still have the orginal problem or what is are seeing the damage from the shotgun.The problem is that all we know we are getting 3, 4, and 5th hand, but based ont the comment that the tech gave that is was caused by the hospital using too much power indicate that he did not know his a$$ from a hot surface ignitor.Some body needs to do some basic obersation and testing first. And that include "interogating" the HO and if needed have them keep a detailed log for a week or two. And that might also have them checking the furnace several times during the day..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Yeah, the tech's an idiot.Re: your second para, give client the fifth degree and the log; We have three comments, day vs nite, a light switch, and outside temp. All three indicate to me that there is a not good quite enough connection or a NQGE component.With NQGEs, temperature or load can make it fail. They are a real PITA to troubleshoot logically. REAL PITA! And trying to use logic can take you down time wa$ting trains of thought. Odds are that you will save money by getting a barely trained tech and telling him to remake and replace. He should have just enough training to read a meter and record the results, make good connections, and not get killed.BTDT many times, got the bruises and the T-shirts.SamT
Yeah, before you start replacing lotsa stuff you gotta get some reliable data. At the very least voltage measurements several times a day (and with loads being varied in the house), and a checkup of the flame sensor, et al, in the unit to make sure there's nothing obvious. If that stuff checks out and the problem continues with the same pattern, a voltage recorder is probably a good idea.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
If the furnace is a high efficiency, condensing unit (PVC vent pipes for the flue), then it is imperative that you look at the manufacturers installation instructions and be certain that the correct diameter and length of vent pipe (pipe plus equivalent length for elbows) is used.
Some brands are very sensitive to improperly installed venting, and will create nuisance trips. Sometimes, improper outdoor terminations will create problems if they exit the house on the predominant wind side.
Also check each and every hose in there on the pressure switches for pinholes or pinch points- but that is less common than venting that is installed wrong.
A common mistake on smaller furnaces is to install 3" pipe when 2" will do the job. It throws off the pressure switches. Another one is vent pipe that is too small on large furnaces- the lack of combustion air in a 2 pipe system will shut down the furnace.