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If if you or anyone else has 10 volts between the neutral and the equipment grounding conductor, you've got some work to do there my friend.

Originally Posted by ComfortablyNumb

I'm still saying bad valve...

Or maybe a grounding issue.

Also just remembered - disconnect the power supply and check for voltage between neutral and ground. Shouldnt have more than 0.5vac if so you may have a neutral/grounding issue. It's put an end to me banging my head against the wall before... on a Trane 90% if I remember correctly. Read between 15-25v while also getting 95-105v hot to ground.

I've measured up to 10 volts to neutral in the past. I thought this was just feedback. Could this be a clue that there is a problem?

Check if it properly grounded,than check gv valve.

If the PS is in series to the gas valve, then my money would be on a volt or 2 drop across that switch

could be bad solenoid coil in valve, weak transformer, voltage drop across pressure switch (check w/ volts not continuity), overloaded transformer (disconnect all peripherals and jump unit out at IFC)

encountered a similar problem (on an l.p. gas system) and found it to be the second stage regulator locking up as soon as there was a slight drop in pressure,

Originally Posted by uniservice

This is one of the times that an old analog meter will be better at checking the valve input than a digital.

thats why my simpson is still on the truck and the guys i work with know to keep their hands off of it!!!

Great idea, disconnecting existing wiring on the valve and running a 24 and common off the low voltage coming in, basically bypassing the board control, then testing the opening of the valve by the outgoing pressure..Thanks!

True, on this particular Trane, the board controlled gas valve on its own mini circuit, per the 12 pin plug.

Originally Posted by Gerbs1983

Removed existing wires from gas valve. Used jumper from r and jumper from common. Once board gave call for gv, manually gave gv 24v from terminal block on board.

Not sure if this is a good thing or a bad thing, but it worked. Allowed us to rule out gv and find the real problem. Also able to determine gas pressure.

I guess it's fine if the GV relay and GV are on their own little circuit. I just grabbed the nearest Carrier schematic I have and it appears the pressure switch has a way back to common thru the CPU, so that unhooking the GV wires would not effect the rest of the cycle. I never bothered to notice whether most furnaces are likewise wired, always assumed all the safeties were wired in series with GV to shut it down if one opened.

Removed existing wires from gas valve. Used jumper from r and jumper from common. Once board gave call for gv, manually gave gv 24v from terminal block on board.

Not sure if this is a good thing or a bad thing, but it worked. Allowed us to rule out gv and find the real problem. Also able to determine gas pressure.

Originally Posted by Gerbs1983

We actually did that on this one. Took 24 v from board to valve, fired gv and ran without issue. Allowed us to rule out any issue w gas valve. First time I have done this, it also allowed us to run furnace long enough to trip roll out for good, leading to the root issue.

How exactly? You cycled normally and added another 24v to the GV, in addition to the 24v it might already be getting?

Or did you remove the existing wires from the GV? If so, how was the circuit completed?

We actually did that on this one. Took 24 v from board to valve, fired gv and ran without issue. Allowed us to rule out any issue w gas valve. First time I have done this, it also allowed us to run furnace long enough to trip roll out for good, leading to the root issue.

Wow. Here I was getting all cockey and raising my hand like Arnold Horshack (if you don't remember him, p*ss off )

I'm a little intrigued by the "2nd transformer" trick in a puzzler like this to quickly and decisively rule out the gas valve. Though I would just use 36" jumpers off the board xfmr after removing R to prevent a cycle. If you hook up your manometer to GV manifold tap, jump the valve and watch the pressure for a five seconds or so; it should quickly confirm the condition of the valve itself, right??? You could keep the valve open as long as you dare since the system would not be cycling and flame rectification would not shut it down.

In cases where the voltage drops so quick your meter doesn't register - like pressure switches that drop in and out so fast they don't even cause an error.

I caught a rudd/rheem late last year, going behind a 30 year tech. Sideways in an attic crawl. GV was chattering and I can't remember why exactly, but I was having trouble deciding if it was the valve or if control voltage was dropping out. I believe in the end I decided that control voltage was on the valve long and steady enough for it to prove flame, so I went with the valve, put it on later in the day and tested fine. But I recall having misgivings until it was resolved.

So anyone else simply jump control voltage to the GV and watch manifold pressure as a quick and easy test? Thoughts?

Originally Posted by Gerbs1983

Yes, sadly I assumed the heat x had been checked during pm, but not the case. I had not jumped out that limit, my fault there. I think an existing problem was aggravated when the pm was performed, because the bad limit had to be removed in order to remove the burners. Good learning experience though, both troubleshooting and learning to not assume the previous tech did everything correctly (check heat x).

Yup assuming has left me scratching my head a time or two... and it always sucks explaining something like that to a homeowner, when your guy was there to assure operation and safety... and now they need a new furnace... hope that all goes well for you guys. I would say that if this were to happen at my company, the new install would be discounted for the trouble... hopefully you have an understanding client! Good luck!

Yes, sadly I assumed the heat x had been checked during pm, but not the case. I had not jumped out that limit, my fault there. I think an existing problem was aggravated when the pm was performed, because the bad limit had to be removed in order to remove the burners. Good learning experience though, both troubleshooting and learning to not assume the previous tech did everything correctly (check heat x).

I had same problem with 90% turned out to be not venting. water backing into vent pipe.

Originally Posted by ComfortablyNumb

Funny how things end up working out.... but didn't you bypass/jump the limits first? Way to figure it out though.

So what about your guy that performed the PM????? He didn't see the dime sized holes? This problem just started the day after? Ouch.

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Funny how things end up working out.... but didn't you bypass/jump the limits first? Way to figure it out though.

So what about your guy that performed the PM????? He didn't see the dime sized holes? This problem just started the day after? Ouch.