Hi!

I am getting at the end of my rope. My problem: the thermostat calls for heat, the inducer starts, but the furnace does not light up. This started about two months ago, intermittently. Recently, it happens more and more often. One way to get it going was to play with the thermostat - first down, then up again - so that the inducer would stop then start again; after a few of these cycles the furnace will eventually start. This worked for a few weeks but now it odes not seem to be working anymore. What still does work is to go at the furnace, turn the power off, and then on again (using the switch on the side of the furnace).

One more piece of info: even when the furnace kicks in, the flow of air out of the vents is 1/3 or 1/4 of what it used to be. Don't know if this is related to the problem above or a different issue altogether (and yes, the filter is mounted correctly - just re--checked).

I have a service contract with NSTAR (live in Cambridge, MA), and they have came out 6 times already. First, they told me they could not diagnose the problem if there was no heat when they actually showed up to my house (waiting 6 hours in the cold with an infant, we tried the trick of switching the thermostat up and down a few times and it used to work). Recently, they got here when there was no heat and decided to change the inducer. No difference - after a couple of days we were back to the same problem. Last, two nights ago I had a guy showing up at 2am (called him at 4:30pm the day before!). Inducer is running, no heat: he switches off and on the furnace, and it starts. Then he says that it worked OK for him. Of course it did not - otherwise, the inducer should have called heat and not just running idle, I told him. Well, he said _now_ it works OK (so, I guess I need to go to the basement and turn on and off my furnace every time I need to start it)? Called them back again, let's see what they say.

Anyhow - what do you guys think it could be, so I can tell NSTAR what to do when they come here? Also, should I just give up with NSTAR and call an HVAC profs (but I did pay lots of $$$ for a contract with them!).

Thanks a million!
FF

Several possibilities, brand and model of unit would be helpful. Problems that are inconsistent are usually the worst to pinpoint, as they tend to run off and hide when the pro is there. Does the unit have a self-diagnostic LED that blinks to indicate malfunctions? After the inducer starts, are you hearing any other sounds/clicks or seeing any other action take place? My initial suspicion is a faulty pressure switch, but to prove it you will have to "catch it in the act". Leave the front access panel off the burner/inducer section for now. The next time this occurs, try nudging the wires where they connect to the pressure switch. If the unit starts working, you probably have dirty/oxidized switch contacts, preventing consistent operation.

Thanks KC13!
Sorry but was trying to make it work with NSTAR, but it did not. Spent two days with them at my place, and furnace is still working erratically.

My inducer and fan for side ventilation start, but furnace does not fire up. Working the thermostat down and then up again, or switching the furnace off and on sometimes do the trick, but not always (and increasingly less over time).

Model is concord 80 plus, vented via the side wall of the house, not the chimney. NSTAR first tried to replace the thermostat, but after a few hours the system started to fail again. So, they came back today and tried to replace the board, but new board (lennox) was not even calling the inducer to work. So, went back to older board, which got the system to operate, temporarily (problem is that when the tech works on the furnace, it tends - not always, but often - to start working, then it fails again in a couple of hrs). However, when the tech put the old board back on, and tried to get it started with the fan for the side venting operating but the inducer disconnected, the furnace started! So, he thought that it could be the pressure switch that stayed open, and replaced it. However, when trying to operate again with the inducer off line, the furnace cam on line again (but it did not when he took the side fan off line as well). Explanation was that the side fan exerts enough pull on the pressure switch to get it going even without the inducer, which should also mean (in his view) that such a fan has enough pull to draw all the fumes out in case the inducer does not start. But I am digressing. Tech left leaving old board on and new pressure switch. System operated fine for about 2 hours, then failed again. Tuning on and off furnace manually only got side fan and inducer going, but got no spark from the furnace (this trick worked until a couple of days ago). I left furnace frest for about one hour, then tried to turn on again using the thermostat, and now it's back online (but of course, it will fail in a few hours, as it has consistently done over the last few weeks).

Any help is MOST appreciated. I have an infant in the house and it's cold in boston!

ff66

Did NSTAR check the flue passage for blockage? Also, try this: straighten a paper clip, disconnect the pressure switch hose from the vent port (not from the switch) and poke the paper clip through the opening to assure it has not corroded shut.

Kc13, thanks again!
There is no blockage on the outside of the house - but no, they have not opened up the pipe to see if there was blockage. Will tell them when they come in a couple hrs. also, I looked at the hose connecting the pressure switch to the inducer, and although I did not disconnect it on either ends, it is very soft to the touch and when pressed it flattens and the returns to its regular round shape - does not seem clogged or damaged at all. I hope this is the hose you were referring to (apologies for my newbiness)?

Also, one additional question comes to mind (probably not related to the outage, but still very important): if the pressure switch gets going due to negative pressure coming from the hose, and the hose is only connecting the pressure switch to the inducer, how in the heck it got activated when the inducer was off line and the only think going was the fan mounted on the side wall venting pipe? The tech told me that it could have been such fan to draw enough to get the pressure switch to engage, but there is NO HOSE by the way such fan and the pressure switch - the hose is only by the way the pressure switch and the inducer, which was offline at the time.

Thanks!
F

Kc 13 (& others),

NSTAR was just here. They just disconnected the fan of the side wall vent (they called it the "girlin" or something like that) and left. Now there is only the inducer fan that pushes the exhaust fumes outside. They told me to call them if the problem comes back (as I mentioned before, the furnace usually works for a few hours after they leave, then it stops working - i.e. the inducer comes on, but the furnace does not spark/light up) and that they are trying to eliminate one thing at a time. From what I have read, I doubt that that could be the problem (plus, I am worried not to have the extra fan drawing exhaust fumes out).

Any insight? Thanks a million in advance!

ff66

The venting arrangement is not exactly "garden-variety", but it sounds as if NSTAR is at least trying to resolve the issue. They may not encounter installations like yours often. I would really recommend the "paper clip" procedure I outlined earlier - it's easy and could eliminate part, if not all, your problem. The metallic fitting that the pressure switch hose connects to is susceptible to corrosion and can close up over time. As long as there aren't holes or splits in the flue pipe, I doubt that disabling the secondary draft inducer will present any hazard.