Shorts/Bad Connections in Robertshaw Gas valves

[SeattlePioneer]

Ok, try this one on;

pre-1995 Heat & Glo 6000 GDV thermopile only valve. Pilot was cruddy and homeowner asked to replace valve, pilot, pilot orifice spud, and thermopile. Fired up unit fine but started ghosting. Damn! Those sloppy vents when HG first went to Simpson DV pipe. I've repaired hundreds of them. Silicone the outer ring & rope gasket then furnace cement the inner sections. Outside, yep, inner sections separated. Tore vent apart, rebuilt Humpty Dumpty then ran inside to test fire. As the condensation is almost completely burned off, I say to the homeowner this was about the point the unit would ghost out when....."click". Dammit! Now,what?

Got my kit, set up readings: 6.78 static inlet drops to 6.02 burning and 5.25 full load in house. 550 mv open, 235 closed. Removed all switching wires so just TP connected to valve. As soon as I jumped it, "click". Fine, I'll fix your widdle wed wagon! Removed TP, installed AA battery pack instead of TP. Jump it at valve, "click". DAMGUMMITT!!! Getting desperate as this is Dec. 23rd 5 pm and I have 3 more stops and another 100 miles to go. Replace valve. AA battery only jumpered--'click'. New jumper wires, "click", tried 2nd new TP, "click". No matter how many valves or TPs the second I closed the contacts, it would drop that bugger out.

Still unresolved. Ok, you guys tell me, what in my panic did I overlook? I know this is a short trip for me but I'm going nuts!
Hearthman

Hey Hearthman----


I had a Robertshaw gas valve that was dropping out repeatedly for no very observable reason. I did everything but stand on my head to no avail, but in an effort to simplify things, I wired the thermocouple directly to the TP ("Ground") connection, and the dropouts quit.

This fireplace had a limit switch wired between the "ground" lead of the TP and the TP connection on the Robertshaw millivolt gas valve.

It' not quite clear to be even after fixing the symptom exactly what the cause of the problem was ---some kind of grounding through the switch, I'd suppose.

But the millivolt reads were all good. When you made the TP/TH-TH circuit to turn on the main burner, the magnet would drop out. Why a bad limit switch would "sense" that circuit being made I don't know.

No big millivolt drops across the main burner circuit even measuring from the thermopile lead, rather than at the contact after the limit switch.


I thought I'd pass that on --- did your problem have a limit switch interrupting the thermocouple to TP connection? If so, perhaps you might have had a problem like this one.




Seattle Pioneer

[hearthman]

No interrupters, no limit switches, no switches of any kind. Just the bare valve wired with either 1500 mv from a AA battery or about 600 mv from a TP then jumping TH to TH/TP with a short 0.1 Ohm jumper that I still use without problems. I even jumped it with my needle nosed pliers and a paper clip individually--click.

I'm thinking bad batch of valves. When the main operator tried to open, it was simply too much load for that valve and the EPU collapsed so click. With a quick drop out valve, the EPU and main operator head are separate. However, with these old TP only valves, you have the 9-11 Ohms btw TP and TH/TP along with the ~1.7 Ohms btw TP and TH. Now, if the resistance in the operator circuit is higher, there will be insufficient amperage to support the EPU and it will fail. I've seen operators stick, which is one reason I use the battery pack. Being a DC circuit, I can switch the polarity and unstick an operator sometimes. However, if there is a mechanical failure in the operator, it will draw off all the amperage and the whole valve will crap out, which is what I think is happening here. Both replacement valves had been on the shelf for many years. I'm thinking a newer valve will do the trick along with a TP from another batch. I remember years ago we got a lot of bad TPs. This was right after the NAFTA treaty with Mexico, which is where these TPs are made. Hmmm, maybe Robertshaw wasn't policing their quality during this time period because 6 months later, the TPs were reliable again.

S/P, to address your post, I don't know how a TC would figure in on this as this is TP only. I've seen limits wired in on TP, which as you said is the ground in these systems but there is no wiring in my case. There was enough load in my circuit not to create a high amp. short.

I still think that house was built on an ancient Indian burial ground....

[jetstream]

I'm thinking bad batch of valves.

Both replacement valves had been on the shelf for many years.

The good news for diagnosis is that it was a consistent failure. You should be able to test all three of the valves completely isolated from the fp just using the battery and jumper and prove them good or bad. Also I'd suggest using a powerpile generator and propane torch to power the valve, then t/off the flame and observe operator and magnet dropout timing.

[SeattlePioneer]

I had a circuit board that I diagnosed as being bad on a Payne furnace once ---a really off problem I had never encountered before. Ihad a replacement board available, and when I replaced it, the same oddball problem continued to occur. I figured I'd diagnosed the problem incorrectly and spent a LOT of time looking for another problem.

Finally, I called in a manufacturer's rep to detrmine the problem. The new part was no good in exactly the same way as the original part I'd found.


Sometimes you have to have the moral courage to decide that your diagnosis is correct and that new parts are bad. But that involves a good deal of leaping.

Trying that apporoach with the millivolt gas valve that was dropping out obviously would not have worked.


Sometimes the life of a repairman is filled with woe and uncertainty.



Seattle Pioneer

[jetstream]

Sometimes the life of a repairman is filled with woe and uncertainty.
Seattle Pioneer

I guess these things serve to keep us humble.

[rrolsbe]

I am having strange problems with a pre-1995 heat & glow 6000 GDV. I shorted the over temperature before troubleshooting this problem. The fireplace will sometimes light and run for hours, but usually not. With the pilot light burning and the main burner not on the voltage between TH-TP&TP is around 430mv. When I turn on the main burner, this voltage drops to around 250mv and then slowly drops, over a few minutes, too below 125mv. The pilot light burns strong until the voltage approaches 125mv then it flickers and dies. The main burner continues to burn for around 30 seconds then it also goes out. Not sure why the thermopile voltage drops slowly? maybe there is capacitor in the circuit that is discharging the voltage slowly and the thermopile is not supplying any voltage after the main burner starts? Has anyone on the forum seen a thermopile act in a similar fashion? Is the thermopile bad? To make sure the thermopile was not overheating from the main burner flame, I attempted to shield the thermopile, using a piece of ceramic tile, from the main burners flame. Same results as first troubleshooting attempt. Any advice on the best way to determine what, if anything, is defective?

Model number 6000 GDV "Standing Pilot Fireplace" using natural gas
Serial Number GCN 39345

Thanks Very Much In Advance for Any HELP and/or advice
Regards
Ron

Ok, try this one on;

pre-1995 Heat & Glo 6000 GDV thermopile only valve. Pilot was cruddy and homeowner asked to replace valve, pilot, pilot orifice spud, and thermopile. Fired up unit fine but started ghosting. Damn! Those sloppy vents when HG first went to Simpson DV pipe. I've repaired hundreds of them. Silicone the outer ring & rope gasket then furnace cement the inner sections. Outside, yep, inner sections separated. Tore vent apart, rebuilt Humpty Dumpty then ran inside to test fire. As the condensation is almost completely burned off, I say to the homeowner this was about the point the unit would ghost out when....."click". Dammit! Now,what?

Got my kit, set up readings: 6.78 static inlet drops to 6.02 burning and 5.25 full load in house. 550 mv open, 235 closed. Removed all switching wires so just TP connected to valve. As soon as I jumped it, "click". Fine, I'll fix your widdle wed wagon! Removed TP, installed AA battery pack instead of TP. Jump it at valve, "click". DAMGUMMITT!!! Getting desperate as this is Dec. 23rd 5 pm and I have 3 more stops and another 100 miles to go. Replace valve. AA battery only jumpered--'click'. New jumper wires, "click", tried 2nd new TP, "click". No matter how many valves or TPs the second I closed the contacts, it would drop that bugger out.

Still unresolved. Ok, you guys tell me, what in my panic did I overlook? I know this is a short trip for me but I'm going nuts!
Hearthman

[hearthman]

Thermopiles get old and tired just like us. No, there are no capacitors in this system. The thermopile powers both the safety magnet and the main operator. Have a tech do a full diagnostic checkup and replace the TP at least if not the entire pilot assy. Check gas readings static versus burning. Have tech remove wiring pigtails and straight wire to the appropriate connections with all new Sta-Kons. Check venting for obstructions.

Hearthman

[gasguy]

Here's a couple of tests that should confirm if it is a bad valve


EPU test, Robertshaw valve: disconnect wire from valve body to TH/TP terminal. Read ohms from the wire to the TP terminal. Good reading is 0-13ohms.

Pilot safety magnet test, SIT valve: disconnect wire from soldered terminal on back of valve. Read ohms from the soldered terminal at rear to ground. Good reading is 0-0.2ohms

Operating head test, Robertshaw valve: disconnect all wires from valve. Read ohms from TH/TP to TP. 0-10.9ohms is good. Infinite, bad. Read TP to TH. 1.5-1.7ohms is good. Infinite, bad.

SIT valve: Read TP to TH. Good is 2.5 (+/-0.1) ohms.

Happy hunting!

[rrolsbe]

Hearthman & Gasman thanks for your posts.

I ordered and replaced the thermopile but unfortunately the problem remains.

The installation manual shows only two screws on the control valve but the unit has three, labeled on the red plastic housing as below LEFT side.

()-------------------------------------() TH------------------Thermostat/Switch

() TH---------------------------------() TH/TP Thermopile
TH/TP

()-------------------------------------() TP-----Thermopile--Thermostat/Switch

Is the labeling on the right side correct? I performed all the debug steps gasman recommended follows are my readings they reference my right side labeling.

Wire with tab connected to bottom screw (the wire that routes to the back of the controller)

Above wire CONNECTED--------------------Above wire DISCONNECTED
Readings

TH-TP 11.5 ohms----------------------------TH-TP infinite
TH/TP-TP 10 ohms---------------------------TH/TP-TP infinite
TH/TP-TH 1.6 ohms--------------------------TH/TP-TH 1.6 ohms
From disconnected wire to GND 10 ohms

The thermopile was, I believe, wired incorrectly in series with the over-temp switch. That explains why the pilot went out every time the over-temp switch tripped. The manual shows the over-temp switch wired in series with the main burner on/off switch (which makes more sense). I connected the new thermopile directly between the middle and bottom screws, IE.. no over-temp in series and installed a jumper wire between the top and bottom screws where the main burner switch wires were attached. Bottom line still have same problem as in my original post but I think all of the reading gasman recommenced are correct? Also, the original Thermopile, according to the wire colors in the manual, appeared to be wired reversed. I reverse the red and white thermopile wires connected between the middle and bottom screws but no change. It appears to not be polarity dependent?

Since there is not much else remaining to trouble-shoot, maybe theirs something wrong with the Natural Gas Valve P/N SRV60-522?

Valve labeling info below:

Robertshaw-Grayson
7000 MVRLC
711-701-415 Max 1/2 PSI
REG NAT 3 5" WC
FOR MILLIVOLT SYSTEM ONLY
038246A

Again, Thanks Very Much for Your Posts!!
Further comments welcome..
Regards
Ron

NOTE: white space got removed so formatting got goofed up in this post sorry... I added the ------- lines to try and reformat

[natgastech]

If the pilot goes out before the main burner it is a venting problem . Let me guess that the flame gets blue and ghosty before going out.

[rrolsbe]

natgastech

Thanks for your post regarding my fireplace problem. Your assessment is probably spot on but whats happening doesn't make total sense to me. With the pilot light NOT lite for days, I perform the following steps. Light the pilot light and hold the knob for 60 seconds, then read a voltage of around 300mv at the TP. While still monitoring the TP voltage, turn on the main burner, voltage drops to around 225mv and remains stable for maybe 20 seconds.; thereafter, the TP voltage starts to slowly drop. All the while the pilot continues to appear to burn very strong until the TP voltage approaches around 130mv. I can understand that the pilot might go, before the main burner due to a lack of air, but why would the TP not produce voltage even though the pilot appears to be burning very strong? For a quick test, I am going to leave the right side of the glass ajar so the pilot/main burner get sufficient air and see if the pilot remains on. I will not leave the unit on for more than a few minutes in this configuration, just what to prove to myself that it is a lack of air problem. Then, after confirming this one way or the other, then I need to figure out how to get access to the venting pipes.

Thanks Very Much In Advance
Ron

[natgastech]

Ron, It sounds like you have a dirty pilot or venting problem because as the main burner heats up it reduces the millivolts. The pilot should resemble a blue torch. If it looks like a candle flame, when the main burner comes on it slowly lifts the pilot flame off the t-pile/ t-couple and results in low millvolts during a venting problem the pilot is affected also. The pilot becomes erratic and reduces in flame intensity, reduces the millivolts. This results in total outages. If the flames are observed to get blue and ghosty and you see the pilot disappear it is only about 30-60 seconds before the main burner and everthing go out. Clean the pilot orifice and assembly and if the flames still get blue & ghosty then it's a venting or seal problem.

[hearthman]

Ron, as you look at a Robertshaw valve with the three screws to the right, they are in descending order:
TH- one from switch leg
TP-one from TP (ground)
TH/TP with two wires- one from the Tp and one from the switch leg
If you have a high limit or glass microswitch, they should be wired in series in the switch leg btw TH and TH/TP.

Why is you high limit tripping? Not a normal event. Does this unit have the red rubber gasket? If so, it needs to be replaced. Not a full CPSC recall but a strongly worded advisory out there.

If you light the pilot and fire the unit, the millivolts from either the TP or TC will spike up then slide down. Usually, they stabilize. However, if your mv keep sliding down, the TP is probably overheating. Is the pilot bracket properly secured (heat sink)? Is the venting correct and inspected clear of obstruction? Vent joints sealed tight? Correct orifice and manifold pressure? Logs in proper position? No homemade pilot shields? Embers correctly placed on burner?

The 522 valve is for quick dropout pilots with a TC and TP or post 1995 units. Your pre-1995 unit should have been TP only with the high limit wired either in seried on the switch leg (N.C. switch) or wired directly to the TH spade on the valve with a N.O. switch.

There should be no reading btw TH/TP and TP because there is a TC instead of an EPU wire. The only Ohm reading on this valve is btw TH and TP, which should be about 1.6 Ohms +/- 10%. Ohm out the switch leg. With this circuit closed, you should be reading about 1 Ohm max or less. Wiggle and check all the connections. Also, remove the wsk pigtail and crimp on new Sta-kon connectors directly.

So, now I'm confused (normal condition): If you have a pre-1995 unit, why do you have this valve installed? Did you convert it to quick drop out?

Ron, look next to the serial number and provide the 4 digit mfg date code.

Hearthman

[Senior Tech]

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