I found your forum after having some issues with my furnace. Age is unknown because I rent and my landlords are out of town.

When I went to turn the furnace on tonight, nothing happened. House temp registering 68-69 at thermostat, furnace doesn't kick on when adjusted to 72.

Fan will turn on when set to "fan" on.

A/C side works fine.

Cycled through the steps listed here (and on the inside cover of the furnace).
*Set temp on thermostat to lowest
*Cut power
*Turn gas switch off, wait 5 minutes
*turn gas switch on
*Turn power back on
*Set thermostat to desired temp

At this point, the thermostat will click and "heat on" will come on.

Down at the furnace, nothing is happening but the blinking LED.

Code says "23" which is pressure switch obstructed or off.

Turned unit off and checked the pressure switch according to the directions found here (gently sucking and blowing through the hose) and no obstructions were felt.

Cycled back through the instructions and got the same result. The blower won't kick on at all unless the fan is set to on.

Any and all help is appreciated.

Update:

I read up on the pressure switches and what, exactly, they did.

I ran a little experiment and at least for now, the furnace is working.

I said in my last post that I checked the air line going to the pressure switch and it was all clear, so I took the vacuum hose off the switch and turned the heater on... it came on.

I'm guessing this pressure switch was designed as a safety thing, but if it starts with the hose off (everything else came on normally, including the inducer motor), then what could it be?

Oh, for the record, I discovered an "extra" filter... jammed inside the blower. I have no idea how it got there, but could that also have been part of the problem?

(I've changed filters regularly and never saw it in there before, and never had any resistance putting in a new one)

I'm leery of letting the furnace run after we go to sleep... is this worry unfounded?

Thanks

another update =(

Furnace switched off when it reached set temp, and I can't get it to come on again, even after removing the vacuum hose again.

I'm thinking the pressure switch is bad?

How much does one of these cost, if in fact that is the problem?

The 310 is a 80% furnace the pressure switch is a safety for the heat exchanger and vent pipe. If you have a restriction in the vent pipe or collector box it will not close. It will try three times to start if all three times it fails, it locks out for three ours an will try again. You can kill the power going to the furnace and then turn it back on to erase the memory on the control board to let it try again. Check for restricted vent pipe and collector box. A dirty filter has nothing to do with the pressure switch on the 310.

Vent pipe shares space with the water heater vent pipe... and runs up the middle of our two story house (it's in the basement) through the old coal chimney... completely encased in bricks. Any suggestions on that one?

Where is the collector box so I can check it?

Go to the water heater turn the thermostat up on it so it calls to heat the water. Hold a match, cigarette or candle at the vent hood on the water heater it should draw the flame or smoke up into the vent with the hot gas. If not turn the water heater off, just trying to make sure you don't give you or your family CO poisoning and it tells us if the main vent is clear.

Check for restricted vent pipe and collector box. A dirty filter has nothing to do with the pressure switch on the 310.

You. Are. A. God.

I turned everything off (again) and decided to start looking where I could reach... i.e. the vent elbow... took the connecting pipe off and found... taa daaaa!! Dead bird.

Very dead bird. Horray for ye olde shop vac not 3 feet behind me. I left the hose in and sucked up all it would suck, put the connecting pipe somewhat back on, and turned everything on again.

Guess what? HEAT!

Now all I have to do is get the connecting pipe back on the vent elbow... and I only have about half a centemeter to go before the screw holes line up, but it's a tight squeeze and I'm not all that big (read: I'm taking a break from fighting the pipe to come post again)


Thanks!!

Good job. Lets hope it didn't make a nest in the vent pipe also.

Ok, the problem is continuing... and really driving me nuts.

I have replaced the pressure switch (after taking most of the inside vent tubing apart and vacuuming it out to no avail), and it only seems to work when it wants to.

Its an off and on thing. Once I get it running it may run for 4 days with no problem, then I'll go for about a week where I have to go fiddle with it every day at 5am to get it to start so we aren't freezing to death, then it will run fine for a few days, then we start all over again.

Could the motherboard have gone bad? Its like the switch isn't getting current at all, so even if the switch does work, it can't?