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Rick
Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 21765
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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Rick we have chat previously the last was on 19 Nov @ 10:01.

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Rick we have chat previously the last was on 19 Nov @ 10:01. This is on a Reznor FE 100 hanging furnace NG. I had to order a new pilot assembly and the unit will still not ignite. With the thermostat calling for heat and AC is applied to the unit it trys and goes to lockout. I measured the voltage Between the black wire and the brown one it was 7v DC. The unit is hooked to equipment grd and 5 on the ignitor is grounded to the frame. I know there is no gas coming out of the port for the pilot tube when it trys to ignite. I checked this with a lighter while it was trying to come on and yes I can hear the ignitor working. The new pilot assembly is a (110853) and the gas valve is a Honeywell VR8204M.

Let me know when you're at the unit and ready to troubleshoot

Customer: replied 9 months ago.
Rick are you aviable. I just got Wi-Fi in my shop today.

Back online this morning. Let me know when you're ready.

Customer: replied 9 months ago.
Rick are you aviable?

Right now I'm free to help you with this. That may not be the case if you don't get right back to me. But I'm online until ~7 pm EST. I do take breaks. But most likely if there is a delay it's because I'm helpng somebody else and I'll get back to you asap.

Customer: replied 9 months ago.
Ok

So what's the current snafu?

Customer: replied 9 months ago.
The ignitor is firing but I am not getting gas to the ignitor.

Do you have 24 vac at the gas valves PV & MVPV terminals? terminal designation could also be TR & THTR

Customer: replied 9 months ago.
No Rick I read about 7 volts DC.

Do you read 24 vac at the transformer?

Customer: replied 9 months ago.

Do you read 24 vac across terminal 1 (sould be connected to PV) and the multiple ground terminal?

Customer: replied 9 months ago.
off terminal 1 to common of the 24v transformer I read 24v.

Then you have a bad connection between the ignition control and the gas valve.

Customer: replied 9 months ago.
I guess I could soder both ends.

I don't know what you have for leads but based on what you're telling me you have 24 v at the control but not at the valve. The only thing it can be is a bad connection. If the leads look good I'd replace them. You could have an internal break that you can't see.

Customer: replied 9 months ago.
The schematic shows that 1 goes to P. This is a Honeywell valve. I cant see the terminals on the valve because they are facing towards the furnace. The schematic shows 1 to P 3 to M and c is common. RIGHT?
Customer: replied 9 months ago.
I have the furnace temp. hooked up. I have 120v feeding as it would if in service. I have a 3/8 line feeding the gas valve so I can work on it. Could it not be getting enough gas?

Honeywell terminal designation is usually (I've never seen different) PV, MV & MVPV. I can't tell you their relative positions. From the pic I have of your Fenwal PV, MV is indicated and MVPV would be GND/common. It might be easier to just spin the valve so you cn see the terminals.

If you don't have ~24v to the valve it won't work

Customer: replied 9 months ago.
Ok let me try a few things.

As far as gas line size goes, 3/8 (OD copper?) is pretty small even for propane but it might be OK. It's certainly enough to light the pilot

Customer: replied 9 months ago.
Is TH or MV and TR or PV_MV the coil for the pilot? I will try a larger line, but I think the problem is electrical.

I agree the problem is electrical. Electronic ignition valve terminal designation is PV, MV & MVPV

Customer: replied 9 months ago.
Can I get back to you later? I have a few things to try.

I'm here until ~ 7 pm EST other than breaks. I'll respond as soon as I can

Customer: replied 9 months ago.
Thanks Rick.

My pleasure

Customer: replied 9 months ago.
Rick the furnace is lighting off but it will only burn for about 3 seconds?

Sounds like a flame rectification/sensing issue. Check the flame sensor, sensor lead

Customer: replied 9 months ago.
Is this the flame sensor probe doing this?

If the flame drops out that fast it's almost always the flame sensor

Customer: replied 9 months ago.
This is a brand new ignitor kit.

Is the pilot flame enveloping the flame sensor?

Customer: replied 9 months ago.
I will check that. Is their a way to wire around it to see if this is it?

No work around. The flame sensor puts out a tiny amount of current measured in micro amps when it is sensing the flame. So any stray voltage can foul up that signal. You can get stray voltage if you don't have a good chasis ground connection to the ignition control. In this case the mounting screw holes are metal lined which is supposed to provide the chasis ground when it's mounted to the unit.

Does the pilot continue to arc once the pilot is lit?

Customer: replied 9 months ago.
Rick I have a 5/8 of 1/2 id now feeding the unit. The ignitor comes on and in a few seconds it lights off. It will only run for a few seconds after the main burner fires off.

Ok, if the igniter stops arcing then something other than flame sense is causing this to drop out. Next time fire it up but have your meter probing the 2 terminal and the common. If 24 v drops out you need to trace back along that lead and jump out each device one at a time until you find the one that's causing the problem

Customer: replied 9 months ago.
I hooked my voltmeter up like you said. when the ignitor comes on the v drops down about 4 or 5 v and when the burner comes on the v drops about 10v and it just keeps cycling.
Customer: replied 9 months ago.
I am using a 40 va transformer.

You need to track down where the voltage is dropping out. I only see a limit and draft pressure switch in that leg of the circuit. Maybe jump out your thermostat too.

Customer: replied 9 months ago.
I am not using a thermostat, I am using a jumper.

Ok then the limit and the pressure switch

You said you had 24 v at the transformer. You have to track down where that's getting lost

Customer: replied 9 months ago.
Wiill do.

OK

Customer: replied 9 months ago.
I jumped both the pressure sw & the limit and it is still doing the same. My way of thinking it is not the limit or the pressure sw because they are in series and grd to term never looses v.

Maybe a bad connection between. Put one probe on common the other at every connection point on that circuit all the way back to the transformer

Customer: replied 9 months ago.
Can it be that the gas valve is grounded on the main burner side. I grd one side of my voltmeter to the frame of the gas valve then took the other lead to the terminal of the main gas burner lug and read continuity.

I've never had occassion to take that reading before. I couldn't tell you if it's an anomaly for sure or not. Seems like you shouldn't read continuity but I don't know. I thought this was a new valve. If you remove the lead from MV does the voltage down stream recover?!

Customer: replied 9 months ago.
it does. Can you recommend the right valve to replace this one?
Customer: replied 9 months ago.

Then the above linked valve is suitable. It has a 150k capacity and since your unit is 100k this will do the job.

Customer: replied 9 months ago.
I just ordered a new gas valve.

Ok

Customer: replied 9 months ago.
Can we leave this open for a little while?

This thread never goes away. You can always access it

Customer: replied 9 months ago.
Should I go ahead and rate you now?

I'd appreciate it. I'll answer related follow ups even after you rate me favorably

Rick and 5 other HVAC Specialists are ready to help you
Customer: replied 9 months ago.
Rick are you aviable?
Customer: replied 9 months ago.
I have a thought. I got another gas valve and it is still doing the same thing lighting off for a second or two. The gas valve says the amperage is .5a. I have a jumper wire across the thermostat terminals. Could it be not staying lite because their is no anticipator in this circuit?

Heat anticipators don't fnction during start up only on shut down.

Customer: replied 9 months ago.
Something is preventing the burner from staying on. As you said their is only 2 things in that circut and they are in series with the circuit.

Wiring diagram shows draft pressure switch and the limit in series between the stat and the ignition control. Since you have the stat jumped out and you have 24v at the transformer and a new control then the only thing left is one of those 2 devices. So easiest option would be to jump them out 1 at a time and see what happens. Generally you can't jump out the draft switch until after the draft inducer fan starts.

Customer: replied 9 months ago.
Ok I will try that. I didn't know that about the draft inducer switch.

Good luck

Customer: replied 9 months ago.
Rick the pressure switch was the problem. I jumped around it when the burner lit off and it went to working as it should. What is this pressure switch? Can I jumper it out?

The pressure switch proves that there is adequate draft present. So it's a primary safety device and can't be safely bypassed. If the switch isn't closing then either the switch is bad, draft is inadequate or the tubing connected to the switch is blocked. Since the only way to confirm adequate draft (check for obstructions in the fan blades or exhaust vent) is with a (pricey) manometer, once the other things are ruled out replacing the switch is a resonable approach.

Customer: replied 9 months ago.
Do you have a part number for the switch?
Customer: replied 9 months ago.
There are 3 different switches shown does it matter which one?

Note the associated dates. Switches usually have a pressure rating on them in inches WC. Usually a fraction of an inch. If your switch has such a spec then you can even use a generic switch. If you don't know the date of manufacture give me the serial number and I'll see if I can find it.

Customer: replied 9 months ago.
AD166M4N60870

My source puts an AD date code at 1978. I doubt this is possible since unit heaters that old didn't have draft inducers. All that leaves you with is the info on the switch.

Customer: replied 9 months ago.
Ok I will look.

You can always contact a Reznor dealer for that part.

Customer: replied 9 months ago.
Ok Before I had the fire with the furnace ( which was my fault ) I had the pressure switch jumped out and the unit worked.
Customer: replied 9 months ago.
I had the venter relay switch jumped out not the pressure switch.

It will work but like I said before it is a primary safety device. You risk filling the space with exhaust should the inducer not work when the switch is jumped out