Intermittent problem (now permanent).

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Intermittent problem (now permanent).

Postby pvstansel » Mon Dec 09, 2013 11:21 am

I have 2x Tempstar Heil NTxx series units (both about 15 yrs old) (dual zone home).
Both units are installed horizontally in the crawl space. Natural Gas. System also has 2x AC compressors.
Up until now, both units have performed well.

On one of the units, I'm noticing the following behavior (note that for the last year, this problem was intermittent. Now it is permanently not working).

(Note that I had posted this intermittent problem last spring, but my description of the behaviors and terminology was not all that accurate).

Better Description of the problem.
(the fan setting on the thermostat is set to "AUTO").
BTW, I'm not 100% sure this is the sequence of events but here is what I think is happening.

1. When calling for Heat, the Squirrel fan kicks on and runs (safety / clear flu / positive ventilation).
2. There is a diaphragm/switch which senses the flue is safe/ready, and signals the ignitor to switch on/glow?? and the gas valve to switch on.
3. After the expected delay (time running the Squirrel fan (est 60 seconds), there is NO glow on the ignitor and NO clicking from the gas valve.
4. I swapped the diaphragm/switches from the two units (good one and problematic one) and the problem did not 'move'. Therefore I'm assuming the diaphragm/switch is not my problem. (they are the same WF) I also verified that there is no obstructions or debris in the vent to the roof.
5. ... the Squirrel fan will continue to run until I turn off unit (Don't call for heat).

I'm looking for any tips on next steps. Getting to my units is challenging. Therefore I'd like my trips in the attic to be productive.

Check volts on the ignitor?
Check volts on Gas Valve?
Tap Gas Valve with a hammer?

thank you.
pvstansel
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- Intermittent problem (now permanent).

Postby pvstansel » Mon Dec 09, 2013 12:47 pm

And (of course) as I was building up courage to climb back up in the attic, the system started working again. So the operative word for my problem is Intermittent. Thanks in advance for any tips.
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- Intermittent problem (now permanent).

Postby Freon » Mon Dec 09, 2013 4:46 pm

First thing to do is TEMPORARILY jumper the inducer system pressure switch. That way you will know for sure the inducer pressure switch is not preventing the ignitor from glowing.
Have someone call for heat while you are in the attic. If the ignitor does glow and gas valve opens with the inducer jumped then check all aspects of the inducer assembly and flue because that is your problem. You may need to oil the motor or clean the squirrel cage or clean the tube from the pressure switch.

If the ignitor does not glow with the pressure sensor TEMPORARILY jumped, then you may have a control board issue. I say that because of this event you - "the Squirrel fan will continue to run until I turn off unit (Don't call for heat)."

Usually the inducer will continue to run for so many ignition attempts. If there is no flame after, say 5 ignition attempts, the control board should shut off the inducer and lock the system requiring a reset. Check your installation manual for the exact sequence for lockout. Possibly you shut off the furnace before lockout, I don't know. But first verify that the inducer assembly is not the problem before looking to the control board.
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- Intermittent problem (now permanent).

Postby pvstansel » Thu Dec 12, 2013 5:43 pm

My furnace is/was acting up again.
I did the jumper test, and still no changes - thus I think we've eliminated this as a culprit. And of course I reconnected the pressure sensor wires.

I did notice something I did not before.
The squirrel fan runs as I've stated. But it IS currently giving up after about 4-5 minutes or so (shuts off). (previously I stated it'd run forever). Infact I still believe it has been in a state where it has run 'forever', but now am 2nd guessing myself. It could be a variation. My furnace does not have a reset button or LEDs that I know of.

So while up there, I very gentle tapped on the gas valve w/ a hammer - and unit immediately came on!

I'll try and repeat this when things act up again.

Thots?
pvstansel
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- Intermittent problem (now permanent).

Postby Freon » Fri Dec 13, 2013 12:14 pm

You are on the right track. Keep testing the gas valve with gentle taps from the HANDLE end of a hammer (wood or rubber). It is possible the solenoid is weak or getting stuck. If you find a consistent pattern of furnace starts with the help of the tapping, I think you have found your problem. I know it's a PITA to get to the furnace but this procedure is the only real way to make sure you're not throwing parts at the problem.
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- Intermittent problem (now permanent).

Postby pvstansel » Fri Dec 13, 2013 4:40 pm

Freon,
So heater acted up again, I tapped valve, and it came on (this is my 3rd iteration of tapping valve).
Recall that I have 2x identical FAU (2 zone).
As I size up replacing the valve (or potentially stealing the good valve from the barely used unit as a short term solution), I have a few questions.

1. To fully remove the valve, I need to remove the manifold/pipe (4 screws). To remove the manifold/pipe from the valve, I need to take off a plastic housing on the valve (#15 torx (with a hole in it)). Otherwise, I can not spin off the manifold/pipe as the valve will not clear the elbow in the pipe/manifold. Does this sound correct?

2. All the gas pipe connections are super tight, and there is some very hardened pipe dope. What is the best way to remove these fittings without damaging things? Should I use a vice or ??

thank you for your continued help.
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- Intermittent problem (now permanent).

Postby Freon » Fri Dec 13, 2013 8:59 pm

First, make sure all power to the furnace is off.

Get the make/model number of the gas valve and research problems and cost just to be sure there may not be an easy fix and that buying may be less hassle than stealing a used valve that could fail next month.

I do not know your particular furnace so I can not give you detailed instructions. Always mark very carefully all electrical connections on paper so replacing is easy. You understand how the valve must be removed so do it carefully documenting each step for easy reassembly.

They may have used pipe dope that contains linseed oil. By now the oil has turned hard. You may need pipe wrenches to break the connection. Make sure you use gas approved pipe dope when you reassemble. And use a soapy water spray on your new connections for gas leak detection.

Once you know the gas valve price, call an HVAC shop and get an estimate... replace this make/model gas valve. See the cost. It may be money well spent. Explore all options.

Good luck. You did well in your diagnosing.
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- Intermittent problem (now permanent).

Postby pvstansel » Wed Jan 01, 2014 5:15 pm

Freon, just to close out on this -

I bought a new replacement Honeywell smart valve (about $170)
I opted to have my local HVAC guy install the valve ($60 labor). This was money well spent as getting the pipe and manifold off the old valve and onto the new valve was more involved than I expected. (And he was very complimentary of the diagnosing work).
Problem seems to be fixed!

Thanks again for your input, help, and guidance. And thank you to the forum.
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