HVAC Experts - I Have No Heat!

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threeputtpar

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So, it was finally cold enough last night to fire up the furnace. Problem is, that it will start the exhaust fan (inducer some call it) but that's all it will do. No gas smell, no audible sound of the igniter clicking, and no forced air fan running. Here's a pic I found online of what the insides looks like:



My father is an HVAC guy, but since he just had hip surgery he's in no shape to fix it this time. I've read online about a pressure switch needing to see vacuum when the inducer starts up, otherwise the igniter and burner will lock out.

Can anyone point me in the right direction as to what I should be examining tonight when I get home? Is the pressure switch the round black oil filter looking thing in the middle of the picture towards the bottom? Or is it the round silver object in the dead center of the pic? Maybe I should have looked over the old man's shoulder more often and learned some of this stuff.

Thanks.
 
I'm not an HVAC guy, but is there a gas shut-off valve near the furnace?

I say this because I'd shut off my gas to the furnace last summer and then it took me a few minutes to remember that when it wouldn't start up last Fall.
 
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Insure that the gas is turned on and shut off the breaker to the unit and turn it back on and see if it will reset.

I am from Wisconsin and we always had a 2nd source of heat - wood heater, etc. Came in handy once when a major ice storm took down all the electric lines.

Must say that I don't miss the ice, snow, & cold at all!
 
Yes, that silver thing in the middle appears to be the pressure switch. You can disconnect the small plastic tube coming out of it and very gently blow/suck on the tube to see if the pressure switch itself functioning. One cause of the pressure switch not working is that the exhaust fan and/or duct is plugged by debris (dead animal, etc.), not allowing the fan to blow outdoors and create the signal to the switch.

After this simple check, you might need a multimeter and go through a diagnostic list. But, the pressure switch is a good start, because it is in "front" of the ignitor, gas solenoid, etc..
 
Originally Posted By: doitmyself
Yes, that silver thing in the middle appears to be the pressure switch. You can disconnect the small plastic tube coming out of it and very gently blow/suck on the tube to see if the pressure switch itself functioning. One cause of the pressure switch not working is that the exhaust fan and/or duct is plugged by debris (dead animal, etc.).

After this simple check, you might need a multimeter and go through a diagnostic list. But, the pressure switch is a good start.


Thank you, I appreciate the help. I did ask my father, but since he's laid up he can get over to my house and he's not that technologically proficient that I could get that picture to him.
 
If there is ZERO activity apart from the DI fan starting (no ignition attempts etc) then yes check continuity across the pressure switch terminals, which should be present after inducer starts up. If not check the venting and/or switch itself.

If that all checks out, check continuity across your flame roll out switches and the high limit switch.
 
Originally Posted By: jrustles
If there is ZERO activity apart from the DI fan starting (no ignition attempts etc) then yes check continuity across the pressure switch terminals, which should be present after inducer starts up. If not check the venting and/or switch itself.

If that all checks out, check continuity across your flame roll out switches and the high limit switch.



If I find the pressure switch to be the root cause, am I safe in jumpering the two wires that go to the switch so I at least have heat tonight? We have 3 small children and our fireplace is not able to heat the whole house. I would replace the faulty switch in less than 24 hours.
 
Originally Posted By: Donald
Why are you asking us when you can ask a pro, your father? Certainly he can answer questions and point to things in a picture to check.


Im sure that there are plenty of highly knowledgable folks on here willing to help.

That said, this is the opportunity for the father to supervise and the son to try to do some work and learn the process and job. Even if I had zero desire to become an HVAC tech, id be jumping all over the opportunity to be an apprentice for the day.
 
There is also a tiny red button on the inducer that is an over temperature switch. Press it to see if it resets, or use a multimeter to make sure it is failed open.
 
Originally Posted By: JHZR2
Originally Posted By: Donald
Why are you asking us when you can ask a pro, your father? Certainly he can answer questions and point to things in a picture to check.


Im sure that there are plenty of highly knowledgable folks on here willing to help.

That said, this is the opportunity for the father to supervise and the son to try to do some work and learn the process and job. Even if I had zero desire to become an HVAC tech, id be jumping all over the opportunity to be an apprentice for the day.


I've been his apprentice for the last 30 years every chance I got, but since he had a new hip installed on Tuesday he has to sit this one out (pun intended).
 
3 small kids, a gas furnace, and you want to bypass safety switches?

No. It's not worth it. Odds are nothing would happen but what if the "once in a million" chances does.

The kids can "camp" in front of the fireplace tonight.
 
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Originally Posted By: threeputtpar
Originally Posted By: jrustles
If there is ZERO activity apart from the DI fan starting (no ignition attempts etc) then yes check continuity across the pressure switch terminals, which should be present after inducer starts up. If not check the venting and/or switch itself.

If that all checks out, check continuity across your flame roll out switches and the high limit switch.



If I find the pressure switch to be the root cause, am I safe in jumpering the two wires that go to the switch so I at least have heat tonight? We have 3 small children and our fireplace is not able to heat the whole house. I would replace the faulty switch in less than 24 hours.



No. Never, Ever do that.

Even on a sealed combustion chamber. The pressure switch is first line of defense venting irregularities, and further I'm positive that action violates your local gas code.

Don't mention to your dad that you considered that
wink.gif
 
Roger that on not jumping the wires. I did see a couple of mentions on Google searches that some techs use this as a diagnostic tool to rule out a bad pressure switch.
 
Do you have access to your outside exhaust? Can you feel something blowing out when the blower is running?

Ditto on checking the overtemp reset.

Do you have a glow plug ignitor near the burner that lights up? I thought these were more common than spark ignitors, but I could be wrong. They can burn out.
 
Wow, I have several things to look at this evening. Here's how I'll attack it:

Check flue output outside to see if anything is blowing out when inducer runs. I'll check the intake also, as I do have a 3 year old boy that likes to hide his toys everywhere.

Find the reset switch on the inducer and press it, and also the same with the rollout switch.

Inspect all drain lines to see if any of them are clogged. Clean as necessary.

Voltmeter the pressure switch to see if resistance is 0 like it should be or infinity.

Pull the lower cover and view the operation of the burners and glow plug/igniter, which ever one I have.
 
Yes,you can jumper it for testing, but testing only. you can't leave it jumpered that for the entire night away. Wait for the exhaust fan to turn on, then jump the wires (i think on most fernances it will sample for 30 seconds before pass or fail) then it will start the ignition sequence and the gas. The reason you can't just jumper it for the night is because the furnace will start the cycle and see that it's a closed connection (jumpered) before it's even started the cycle. Under this condition most circuit board will register this a fault (as it should) and not start the unit.

Keep in mind this could still be a problem with a clogged hot air outlet. still needs to get investigated even is this test is successful.
 
Too late now to simply spend the $100 for a tech to show up(your dad could likely hook you up with a contact) and get it fixed.

I only state this because I saw 3 kids and freezing.....
 
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