Thanks for the vid. I am at the 8yr mark and this is the kind of intermediate to advanced stuff that will get me to improve. I do maintenance and have largely learned from KZfaq and books. Nobody working around me (including my vendors) seems to know anything. They are part changers. I've stopped calling vendors, because they screw things up worse than the original problem. These videos are very much appreciated. I've learned something in just the last day from watching.

I know this is an old video but it was really helpful to see that diode bridge and understand why some two stage valves cannot be "ohmed out". I was convinced it was bad until I watched this video. Instead, I applied 24v between common and PM or H and it went "click" each time. This convinced me to install a new (used) board and it fired right up. Thanks!

I managed to fix the broken thermocouple! The problem is that most online videos tell you to test the TC mV output. In my case the mV were within range, however the key is to ALWAYS test BOTH the mV and the Ohms. Given that my TC had good voltage, I went to check the solenoid(which seldom fail as the wire inside is quite thick) At first I thought it was shorted, but that's my ignorance! A very very low resistance is essential for a working solenoid. SOLUTION: FIX THE FAULTY THERMOCOUPLE: So here is a FIX that may help many readers out there. I grabbed the tip of the thermocouple with a pair of pliers and the tip snapped off! EXCELLENT sign! It had badly oxidised inside and became brittle. This is the part where the two metals are welded together(copper or copper nickel alloy). So I removed the inner STEEL wire and cleaned it. I also used a small drill point to clean out the inside of the outside sleeve. Some grey powder came out, sign of a burnt out joint. Now, for a temporary fix, one can reinsert the inner steel wire and crimp the tip to the outer sleeve. I chose to fix it permanently. If you have access to a spot welder or are practical with a stick welder you can carefully spot weld the tip of the TC so that a small bead forms. I welded the inner steel wire and outer sleeve with a brazing rod 15% Ag. It is easy to do with an inexpensive MAP gas torch (if you don't have Oxy-acetylene torch). Solder is not suitable because of it's low melting point. If you have access to a spot welder or are practical with a stick welder you can carefully spot weld the tip of the TC so that a small bead forms. Thank you grayfurnaceman for your excellent videos

Well, the rectifier thing I found out at night with below zero temps and no available gas valve. Bypassed the rectifier to get the valve to work. Was unsuccessful but I learned something. Thanks for the support. GFM

Another great video that digs into the guts of the valve. Not sure why people click thumb-down?

Thanks for the support. My hope is to make concepts easier to understand. GFM

The pilot solenoid would normally have a very low resistance. Make sure the button on the thermocouple is clean and has been tightened. Do not over tighten. If the pilot light is covering the thermocouple 3/8 to 1/2 inch it should hold in. Check out "the pilot gas furnace" playlist for more info on how the pilot should work. If it still does not work, the gas valve will have to be replaced. Good luck and let me know what happens. GFM

Thanks for the explanation GFM...Your site is like taking a "Furnaceman" college course on fundamental electronics and how it effects everyday technology in our homes. Fantastic job, keep it up

Thanks for posting. Even though it was a long time back it has helped me today. Having used a number of your videos to identify the gas valve as the most likely cause, I metered it and found it to show a resistance of about 2 ohms and close to a 5 amp draw (rating is 0.5A). Removing the plastic cover of the Honeywell VR8215 series valve revealed a small board with discrete diodes and a capacitor. Having replaced the 4 x IN4007 diodes the resistance is back into the 2 mega ohm range. This replacement was possible without removing the gas portion of the valve.

I've often wondered why I can't diagnose a new style white Rodgers valve with ohms. My meter also doesn't do mega ohms. I've seen some read 0 ohms and still operated. Saw 90 and the valve didn't open. This helped me understand this.

Sometimes I assume more than I should. In most cases, we are looking for 24-28 volts AC. The voltage is transformed from usually 120V AC. On some units, specifically hanging unit heaters, the gas valve can be 120V AC. Thanks for the comment. GFM

That's the goal! Thanks for the comment. GFM

If the valve is working ok and it is not objectionable its fine. Not all valves run on DC. Merry Christmas GFM

Finally an answer to my question. I have asked HVAC techs why my coil reads open, and no one knows what I am talking about, which I find hard to believe.

30 year old Bryant 394GAZ upflow furnace using the White Rodgers valve you have in the video. No problems with this unit until 2011 when they replaced all the gas mains in town with plastic. Last few years the orifice on the #1 burner (out of 4, 100k BTU) keeps getting clogged but that's nothing major... wondering why though. I have been fighting with this furnace all winter. Was without heat for 3 days in December waiting on a new pilot assembly (flame switch went bad so pilot kept going out). Ever since the trouble with the pilot began, the furnace has multiple clicks when energizing the main gas valve. Sometimes it acts normal and just one click, other times it's a dozen clicks. I have already replaced the lockout ignitor (no success, intermittently failed on the pilot hold circuit), wrapped the wire for the main valve circuit in tape in case there was broken insulation somewhere (yes, electrical tape), checked for arcing behind lockout, and redone all the solder points for the main valve in the ILO and all of the ones on that stupid circuit board on the gas valve. All to no avail. Tested gas valve solenoids with circuit board removed and got around 960 ohms. No exploded/bulged capacitors I can see in either the ILO or the main circuit board in the blower section either. Got another 2 months of winter to go here and I don't want to be left without heat again. Am I looking at getting a new valve? Any other suggestions? Oh, and I forgot to mention that you can hear the solenoid clicking throughout the entire house through the ducts... haven't been watching much TV or anything so it's pretty quiet in here.

Most of the valves have a rectifier as said on the video. So sometimes the reading will not help. If you can hear a click when the pilot proves, the solenoid is energizing. I believe that pilot has an integral flame rod. That just means the rod that the ignition spark comes from is also the sensing rod to prove pilot. Try sanding the flame rod if you dont hear the click. Good luck. GFM

Yes you could. The amp meter must read in .01 increments. And remember on newer units the gas valve is only on for 4 to 7 seconds on a trial for ignition. So the sequence is inducer on to prove pressure switch>HSI warmup>gas valve for trial for ignition. GFM

Could you show where you are connecting the multimeter to test resistance on the solenoid?

The red and white are the wires going to the thermostat. You are jumpering out the thermostat to eliminate it as the problem. GFM

Natural gas piped in city, hot water heater doing just fine, gas close dryer all good. It is now working just fine but would not light up twice last night, When it first started do this it had been off and cold now it is hot and doesn't get cold well not ice cold. Something is not getting th message to turn th gas on. I just don't know enough about how this works, it is old 1983 but real clean and broken. Was just trying not spend th 4,500 for all new and maybe not as well made. Thanks for ur time, it's been fun, never did this before..........T

Thanks for the Good luck  and suggestions. The very first think I did was cleaning both rods. What is the purpose of having 2 rods? .One integrated with the spark, and one on the opposite side of the burner? Do they prove pilot flame or main gas flame, or may be one is for pilot and one for main gas flame. The reading should be 0.15 micro amps. I don’t thing I heart clicking from the gas valve .When properly working the main gas shoots immediately after the pilot.

I went today to that rooftop equipped with valve and control module. I measured the voltage to PV -24V, measured to MV (after pilot was on) no voltage .So -it is the module? Then I jumped PV to MV after the pilot was lit- nothing happened. That left me clueless .Install the new module (universal) -no main gas .Swap the valve (universal).Clean main and pilot burner. That took some time. Bingo! Works. Swap the old module back .Works as well.

I think the "rapid expansion" occured around the time the thermostat reached the temperature to shut the boiler off. The house was already heated. I am not sure if this is the circumstance you are describing. Thank you GFM for the quick reply and details.

Unfortunately the valve must be replaced as a whole. It is probably best as inside of the valve is quite delicate. Thanks for the question. GFM

I am assuming the pilot flame is reasonably large and blue. I would clean the flame rod. It is in the pilot assembly. A dirty flame rod does not send a large enough signal to the board to prove flame. Hope this helps. GFM

It sounds like you have more than one problem. If the transformers are wired together, I recommend you use one of a higher capacity. The explosion (we call that in the HVAC trade a rapid expansion lol), would seem to not be related to the transformers. I would watch the ignition for delays between burners or simply a delay to light. Watch it you could get a face full of flame. You may want a professional on this one. Hope this helps. GFM

Sir, thank you very much. This is exactly what I wanted to know. The pilot lead to the circuit board is shorting out. It took me a month to figure it out. It was a intermittent issue that was causing the problem. I really didn't know how that black box was connected to the coils. My valve is very similar to this one shown. So, I need to take the circuit board out and somehow fix the pilot lead. I see from another video these leads corrode.

That is Full Wave Bridge rectifier, now that you removed that part, you now have access to the coil or coils, and you can use the ohmmeter on it. You can also connect the 24-28 VAC input to the external spade connectors and test the Rectifier to see of it has a DC Voltage output!

Checkout the GSI from Amazon. It is sold under several names. Its kind of a cheapo but it does work. No endorsement here. I did a vid on it. Look for GSI in the search box. GFM

First off, Great videos! Super job all around even for the novice repair person, Great education, We have a mid/late 80s Lennox furnace G16Q3 It has the Robertshaw ignition module. Last spring when we turned the power off to the furnace it was not running properly and we knew this year it would need some repairs. (Blowers running to long/and not lighting very often. long story) Originally we were told that we should replace the ignition control module. We seem to have more than one problem. first problem was no spark, after cleaning both igniter and sensor still no spark and realized the igniter wire was faulty and replaced it and we now have spark. We do have power going to the gas valve and are trying to determine if we need a new valve and/or still replace the ignition control module? That being said we also had weird problem originally when cleaning the furnace this year. I had a drop light and was holding it close to the furnace so I could see into it. The bulb touched part of the furnace and sparked a very loud pop, and tripped the breaker to the furnace. The light bulb went out but came back on after turning it back on. The spark was on the gas supply line going to the burners. at this point power was off to the furnace as I was going to clean it. It left such a spark it removed the paint on the gas line. Do you think that could have ruined the gas valve? and also should we still replace the Ignition control module? Scratchin my frugal head. Any help would be appreciated. ty

Video series like this are changing the landscape of education. "HVAC today... Brain surgery tomorrow. " Watch out, high-paid doctor rackets.

Sounds like there is not enough amperage available to hold the valve open. Jumper red to white on the thermostat and see if it does the same thing. If not, the thermostat is bad. GFM

Great information, you really know your stuff. Enjoy the videos.

Without knowing details (mfr. model no, etc.), I'd guess the rectifier is there to provide DC power to other circuitry in the control module, and/or DC power to a solenoid, since they don't work with AC. Supply is probably either 110 VAC or 24 VAC, which needs to be converted to DC, since that's what most IC's work with (generally +5VDC for old TTL logic, lower for later IC's). I came here looking for info on REPAIRing older valves, i.e. pulling out and replacing the safety magnet or repairing the hold-in coil on a Robertshaw 110 series, after verifying thermocouple output (30mV) and continuity of the coil. At least you went into more detail than most "repair" videos I've seen - most just show how to replace the whole thing, if that. I've kept an old 50's era Coleman floor furnace going for years by re-greasing the valve (LP gas is a solvent for the grease they used back then). Hoping that's what my problem is. Thanks anyway for a better-than-usual video.

There is a wall mount heater that's been running fine. I'm sure it doesn't use as much as the furnace. Gas flow seems fine.

I got 15 volts coming in when I turn on the fan. 24 volts if i put the thermostat on like if the pilot is on. I already check for gas coming into the valve. Also took the tube and pilot out and clean the pilot. Took the pilot out, put the valve on set and I don’t get no gas at all. Is there anything else besides the valve that could be bad? And also is 15 to 16 volts ok for the valve to open and le gas through?

Great Video. Thanks. Also watched your video on the combination valve. I am trying to troubleshoot an old home has heater that will not stay on. Being portable, it has a tilt switch in series with the solenoid. The tilt switch works fine. I tested the voltage on the thermocuple and it reaches 30 mV, which seems to be enough. Then I took out the solenoid and noticed that the ohmmeter tested a short circuit. In other words the brass chassis is not isolated from the central contact point. So, I am guessing that my solenoid is roasted! I cannot find a similar one anywhere and so I was hoping you could tell me if you had ever rewired a solenoid. Any other pearls of your wisdom are much appreciated.

On the White Rogers I actually OMed the coil today (with the circuit board removed) it is 91 Ohm for both pilot and main gas (witch tells me they are not shorted) However my pilot is lit and my main gas does not open. I swap the ignition module with the known working one and got the same result. I’m planning to replace the valve tummorow, but still not 100% sure .Any suggestions? By the way it was working intermittently 2 days ago.

I guess I dont fully understand what you mean. I just now put a new transformer rated for 40va. @ 24vac. The honeywell gas valve is old. So what happens is everything seems to function.. It purges THe igniter lights up. And then as about two second after the bruners lights the gas valve starts buzzing. What do you mean by jumper red and white?

I just had an epiphany. To test this valve independently off all other factors would it be practical to simple make turn off the gas and the power to the furnace energize a 24vac transformer and apply it to the coil connections? This way you are eliminating any possible feedback loop issues? If it functions properly (no buzzing) apply gas pressure? (briefly)

Hi, I'v leand alot but not enough. I have an old Day & Night furnace. It has only 2 terminals on the control valve and they are open. I pulled the wires off from the thermopile and the pilot keeps on burning! .Any suggestions? Thank you.

Then I would have to agree it is probably the valve. Good luck. GFM

Ok I put a jumper across the read and white on the mainboard *alligator clips* and cycled the furnace.... Same thing a horrid buzzing from the relay in the gas valve assembly. Someone suggested to me it could be improper gas line pressure? I know that that 8205h is pron to corrosion at the internal board. I have a place ready to purchase a new valve assembly on my behalf but they want 150 bucks! Anymore thoughts?

I have a Robert shaw retro kit, that is intermittent pilot, that pilot light then when main gas valve is suppose to open, it shutters, clicks and clicks, but no main gas opens up, I replaced the gas valve with the same one and same thing, I had 24v at the main valve, so no I just don't get why the chatter , have not run into this problem as of yet, aslo replaced the ign box with same cond.

Very helpful, thanks!

My gas valve will not click to the open position. It's a newer honeywell valve. I tested the voltage going to the gas valve and it does not make it over .90 volts AC after the igniter starts to glow. I checked my transformer and it does put out 24 volts AC. My conclusion is that there is a problem with the control board or a bad wire. Thanks for this video.

if it's a bridge rectifier couldn't you put the meter on diode test and depending on the polarity of the leads on the terminals forward bias one pair of the diodes, should get a little over 1 volt

I have 36C04 222 standing pilot valve. The pilot was not remaining lit. I changed thermocoupler 2-3 months ago. It started the same problem again. No The pilot has 20-30 mV dc circuit (thermocouple) and main valve has 24 V AC circuit. I checked my main gas valve solenoid resitance of 64 ohm. For pilot solenoid the resistance come 0.1-0.2 ohm. Considering such a low voltage, it seems logical to have very low resistance. What is typical resitance of pilot valve solenoid?

What i need to know is what actually goes wrong with the valve as I'm having a problem with the heater suddenly not heating but ruining constantly

It is probably a flame sense problem. check out this vid. Furnace won't start. Check the flame rod.

The pilot stays lit. But when I bypass the thermostat to fire the furnace, I hear the click. But the pilot just doubles the size of the flame. The burners don't ignite. I wiggled the stat wires and I made a hum sound. I'm thinking I have a sticky valve that just isn't fully opening up? Its not been fired in about a year.

The one on the opposite side of the burner is to assure all burners light. If your ign control is a Johnson they seem to prove very fast. Honeywell is much slower. If you have 24 volts to the main gas solenoid valve and the valve does not open, the valve is toast.

Excellent video, I have some of these valves, just had my 1st one go, ( 1988 vintage Goodman) was fun to take the circuit board out, could not see any issues that were obvious. Changed it out with a Honeywell, only one available, and was wondering if there were any serviceable parts, Thanks for your web site and all the great videos ! I learned a lot !

To test the coil, can I put my meter on the "M" and "C" terminals of the gas valve - where an open loop reading would indicate that the coil is broken? and what would the meter read if it were normal? Thank you.

Bir çok insanın derdine çare oldun.

I'm working on an old American Standard furnace. Much of the name plate is worn off, but it's about 65% efficient American Standard furnace. The furnace goes through the steps and the hot surface ignitor lights up, but gas doesn't come out. It was working previously, but someone tore it down, and put it all back together making repairs, and now the gas won't blow. I think it's something to do with the valve. From the module, I have 2 wires going to the top of the valve in terminals 1 and 3 on top of it. 1 and 3 are also jumped together with a common wire. The wire in terminal 1 on top of my gas valve, and the wire in terminal 3 go to my electrical module. I'm confused as to whether the electrical module is wired incorrectly, or if it's the relay on top of my gas valve. Any way, I get 1 red blink from my electrical module when it's supposed to be releasing gas but no gas comes. The hot surface ignitor glows, then shuts off. repeats 2 more times. Any help?

I've learned a ton of good stuff through your videos. Thank you for sharing. I'm looking at an old Janitrol "garage heater" in our workshop. Unit has separate valves for pilot and main burner. Pilot won't stay lit. Thermocouple puts out 21-22 mV in normal position with the red button pressed. Measured 22.5 kOhms across the solenoid, which after watching this video tells me this component has most likely failed. Question: can you still get a pilot-only valve, or will both pilot and main valves have to be replaced with a combination unit?

What brand and model?

Hi, on regular basis my furnace stars and it runs for around 30 seconds and than once pilot lamp turns red, gas release valve releases gas. Lately when I'm having problem in my furnace that gas release valve releases gas ad after 5 second it shuts off gas, it keep doing that for 3 times and after that furnace turns off than I have to keep trying it till it works, can you please tell me do I need to change gas release valve or there is something else wrong in furnace mother board and not in valv

I am getting hight voltage from the gas valve I have and it looks like the same one with the blue knob. I am getting a lockout and the ingniter is new and it just click from and doesn't start. Am I on the right track or should I replace my white Rodgers control unit model 50e47-843 any help ASAP would be great. Thanks

What's going on if you do get humming from the valve?

Hi GFM. Thanks for the vid. Do you know if the coils in the newer valves can be replaced, or if the entire valve needs to be replaced? My valve (White Rodgers 36E98 202) is sticking and requires a tap with a mallet on the "tall" coil to turn on. It is getting 24VAC. This is a Carrier furnace (58PAV11113112) that is about 19 years old.

Why would you not be able to check the solenoid coil with an ohmmeter after removing the terminal block? Both ends of coils are exposed after removing terminal the block. I need to know the resistance of coils. One measures 98 0hms and other is open?

Thank you for ur time! I have a gas fired hot water furnace w/spark to light. Blower comes on pump runs, spark/solenoid happens NO gas to light, keeps trying to light. I turn off unit wait 15-30 mins turn back on and it may light or not, hear solenoid hitting but no fire. This is intermitting.( Honeywell solenoid) Has been working for 12hrs now but may quit at any time. (not servicing this myself) need to steer him, it may not have a problem when he is here. What do you think? Thank you

can you get delayed ignition if you have a faulty gas valve on an old furnace ?

Well, as Sherlock Holmes would say, after eliminating all else, the only answer, however improbable is the one that works. There have been times when I said the same thing and never did find out why. If you find out why, send a note. GFM

So unit works now. But I still have no clue why I did not have those 24 volts to MV It was staring to rain and getting dark -no time for more testing. I’ll try to figure this out on the next job :) :)

I have a bryant gas furnace and sometimes the pilot goes out I'm assuming due to high winds. The furnace stays on with the fan blowing and everything operating as if the pilot were still lit. Because no flame is on the furnace will just continuously running! Should a furnace turn itself off if the pilot goes out? I haven't noticed gas odors when this happens, but concerned.

Ok, so I jumpered the thermostat with difference. I dont have a pressure meter can you recommend a reasonable one? I have to troubleshoot this before I call someone. My money is limited

I wasn't humming, the valve was... lol

Good video! I have a 36c04-208 and would like to convert it to LPG. There doesn't seem to be a kit for it yet my research show its is convertible. Is this converted by just turning the regulator screw under the screw cap outward to decrease the pressure or is this model not convertible?

IM WORING ON A H.B BOILER WITH A INDUCER , PRESSURE SWITCH AND IGNITER . WHEN I TURN UNIT ON THE IGNITOR GLOWS BUT THE BURNERS DONT COME ON. COULD IT BE A BAD VALVE. AFTER 3 TRYS THE BOARD GIVES ME A CODE OF 3 BLINKS THAT IS A INDUCER PROBLEM. WHAT COULD IT BE

This winter when I powered the unit on for the first time and the main burners ignited one of the two transformers had a puff of smoke. I think I wrongly attributed that to being off all summer. Now on the down cycle we heard an explosion that shook my brick building (boilers off now). I could not find any damage, but I did smell an electrical burn. A winter and half ago all the electric blew out on my boiler. I tracked it to the gas valve. WR 26C80. I am thinking the valve is bad again

I recently ohmed a 15 year old goodman furnace valve and a brand new generic replacement valve. Neither of them shows any resistance reading or continuity - simply O.L. Is this also common to get no reading at all?

I have a Williams Monterey 35000 btu wall heater. The pilot it will not stay lit after I stop pressing the pilot button even after warming thermopile over a minute. I ran some tests: I disconnecting the two thermopile wires from the gas valve, connected a meter to them, and I got a reading of 755 mV. Next I removed the gas valve from the heater and connected the thermopile to it. I used a butane torch to heat the thermopile as I watched through the gas line opening to observe the solenoid. Initially while pressing pilot button it was open about 3/16". After heating thermopile, when I stopped pressing it remained open about 1/16". When I turned off the butane torch it snapped closed. Should it be open wider like when I'm physically pressing it?

I recently condemned a gas valve because i wasn't getting any continuity on the coil. I was going to take the solenoid coil out and put it in without having to replace the whole thing. How come that rectifier is interfering with the continuity testing on the terminals? This was a bryant 90%er.

How does the White Rogers work? I have one just like the one you have. I have voltage. When it calls for gas. I have to jar the valve for the gas to start up some time's, some times it works fine. Bought a used one of ebay, Same problem. Don' t seem to be a power supply problem.

robertshaw 7000 model gasvalve fault during ignition solenoid is energies but not open gas there is sound like not enough amp when I closed the regulator knob on the valve solenoid is opend there is sound gas also opened,,,,, every time I have to do this pls help me to do the correct action

I have that very same WR Valve and I today the heat quit. When the furnace kicks on the valve or Solenoid makes several clicking/arc sounds and the ignitor glows but no flame. I've double checked my gas flow and it's good. what would you suggest?

how do you test if power's going to the valve?

it would be nice if you mentioned what voltage we are looking for DC 24?

thank you nice video ,where can we order replacement valves for older miller gas heater ?

I turned on the heat, the motor ran, I was sure the pressure switch closed bc the igniter lighted up, but the gas valve didn’t open. I smelled no gas. Measured the voltage for the gas valve on the control board (blue wire and the common wire and I got about 27 volts. I think but I am not sure that the gas valve is bad. Is there any place else to look? Bought an old gas valve from eBay but haven’t tested it yet. If I take the wires from the old gas valve and plug it in the new eBay gas valve, should I hear a click? Thank you.

Could you use an amp meter ?

I have tested the voltage going to the valve. I read 13V on the valve before the valve is energized. after the valve is energized I read 24v. Is that normal to read 13v on the valve before the valve is energized?

Ive got an emerson 36e36-201 valve. It says 1 2 3 on it. Could you explain what they are and how it needs to be wired? The furnace guy left recently saying I need a board. I bought one. Numer 1 on the valve has a jumper running to number 3. Number 2 has a blue wire and a brown wire. This doesnt seem right?

Do you have gas? Possible regulator problem at the gas meter. Check with gas supplier. GFM

My gas value model 36c03 reads 4.76m ohms so its bad?

What is the on and off switch on the one fas valve for

Question for you sir, on the White Rodgers Valve, you pulled off the black box/circuit can you tell me the gas valve number?

What about ohm meter on the safety valve solenoid???

Using this diagram, you can also test all diodes in that Full Wave Bridge rectifier in that black cap using the diode test function in you Multimeter. search.yahoo.com/search?p=diagram+of+full+wave+bridge+rectifier&fr=iphone&.tsrc=apple&pcarrier=Sprint&pmcc=310&pmnc=120

O yes I also swapped the circuit board and still main gas did not open

Pueden traducir el vídeo a Español por favor.

Waterbury furnace repair

wow sorry for the typos lol

I've given these valves a sharp tap with a hammer and they work like normal. Why?

Thought my coil was open until I discovered that little rectifier in there.

You should mention not to test the thermocouple coil with a 9 volt ohm meter to burn out the coil

what about a continuity test on the valve?