How to Test if Your Fireplace Main Control Valve is Bad
Time to Complete: 5 minutes
Recommended Tools
Test #1 – Resistance Test
One way to test if your main control valve is bad is by testing resistance. We can do this with our Digital Multimeter.
First lets make sure it is in the correct setting. We what it in the Ohm’s setting (Ohms is basically a term that refers to resistance). This is sometimes shown in symbol form: Ω
First, find you need to find “Zero” but touching your multimeter leads together. If it reads anything other than zero, you’ll want to subtract this number from the number you will read on the valve. To test the valve, disconnect all wires from the TP and TH terminals, then place your meter leads on these terminals:
You should get a reading that should fall within the following parameters:
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- SIT 820 ‐1.75 to 2.75 R
-
- Honeywell VS8420 ‐3.1 to 3.6 R
- Robert Shaw/Dexen – 1.5 to 1.7 R
A SIT 820 valve looks like this:
A Honeywell VS8420 valve looks like this:
A Robert Shaw/Dexen Valve looks like this:
Test #2: Thermocouple Magnet Test
Typically, for this next test you may be experiencing random occurrences of your pilot going out. This test is for the SIT valve only. It is a way to check and see if there is something wrong with the valve and not the thermocouple itself.
First, disconnect the all the wires from the front terminals:
Then, unscrew the thermocouple from the valve (the copper colored tube):
Next, you will have to test the magnet on the back side of the valve. Depending on how much space you have, you may have to remove the valve entirely. Here is a picture of the back of a SIT valve
Put your Gardner Bender Digital Multimeter in the Ohms setting. Remember to touch both of your leads together and make sure the read zero. If the do not, you will need to subtract this number from your reading. Now put one lead on the soldered point on the back of the valve and one to the ground:
A good reading here is anywhere between 0 and 0.2. If it is more than 0.2 then replace the valve.
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September 25, 2014
question, my fire comes on fine. however from tome to time it shuts off intermittingly for 2 3 seconds & flame returns? anything I can check
September 26, 2014
Is it a standing pilot unit? If so, check the wall switch or wiring on the valve itself. It sounds like its a loose connection.
September 26, 2014
I did this test and an getting a reading of 00.0 ohms. You have the range listed as “SIT 820 ‐1.75 to 2.75 R” but I assume my SIT 820 control valve needs replacing because to my knowledge there is no such thing as a – (negative ) reading in ohms. Am I right? or is that really -1.75 there? If so my reading of zero ohms would be within the range.
Looking forward to clarification.
Thanks,
Pete
September 26, 2014
Yes, there are no negative ohms readings. The – is meant as a dash not a negative.
September 27, 2014
Thanks for all the info you have on this site. It has been a great help. I will go ahead and order a new control valve.
October 12, 2014
I have a Superior 3 sided fireplace installed in 2000 when we built the home. It has SIT 820 valve. All parts are original and I’ve never had it serviced other than annual cleaning which I do. The problem I’ve been trying to troubleshoot is that the fireplace would run for about 30 min and then go out, including the pilot. This occurred with the logs installed and removed.
1- Pilot flame looks good, nice and blue.
2- Cleaned Thermocouple and Thermopile with a fine sandpaper and blew out any dust in Pilot stem and wiped clean.
3- Tested Thermocouple as per your process. I tested 50 mv which is outside of the operating range you stated (20-30 mv). I then reconnected the Thermocouple to the valve and now the pilot will not stay lit when I release the button, even after holding it in for several minutes. This is strange because we had to light the pilot several times over the past couple of days and we had no trouble lighting it prior to disconnected it to test.
4- Tested for resistance across the TP TH terminals on the SIT 820 valve with all wires removed and I get 2.0 ohms.
I appreciate your thoughts on what the problem might be with keeping the pilot lit. Maybe 50 mv is too high and I should replace it? Could this also cause the original problem with the fireplace going out after 30 min?
Thanks,
John
October 25, 2014
It might be pulling the pilot flame away from the thermocouple as the chimney heats up and starts to draft more. Try to see what the pilot flame does before it goes out. Does it look like its getting pulled away from the thermocouple? You may need a flue restrictor or need to construct some kind of a pilot shield to prevent this.
November 13, 2014
Sounds identical when my control valve was bad and needing replacing.
October 12, 2014
I have a Majestic log fireplace with a Honeywell control valve with thermocouple and thermopile. I can light the pilot light normally and releasing the button after about 40 seconds the pilot stays on.
However, when I turn the controller from PILOT to ON position I hear the valve clunk and the Pilot immediately goes out. I have left the controller in the Pilot position with it lit for ever and hour and as soon as I go to the On position the pilot again immediately goes off.
It appears that the thermocouple is working fine and and the pilot light look good but the valve is not letting me go to the on position.
My thoughts are that the valve has failed.
Anyone seen a coundition like this.
October 25, 2014
This was a defect in Honeywell control valves. Replacing the valve would certainly fix the issue, but the valves haven’t been made in a few years so they are hard to find and expensive when you can find them. Try turning the knob VERY SLOWLY to the on position. A lot of times you can get the pilot to stay on by turning the knob very slowly.
October 19, 2014
Hi,
My Fireplace (Kingsman MQZDV3622 Direct Vent natural gas) is about 2 years old. It’s been working fine until I shut off the pilot light to do some painting.
It is a millivolt system with a SIT valve
The pilot light works fine, flame is the pattern as per the manual.
When I turn on the fire place I get a partial blue flame in the burner even though it’s turned right up. The flame now is only about 1 to 2″ high and does not light up the whole burner. I used to get a nice 10 to 12″ flame.
It does not mater if I turn on the fireplace with the remote or manually, still no proper flame.
I checked the Thermopile and get about 500 millivolts with the burner off. When I turn on the burner it drops to about 212 millivolts.
I checked the resistance of the valve and get 2.0 ohms (SIT)
I thought I might be having a gas pressure problem, but my York high efficiency furnace works fine which feeds off the same regulator.
What could the problem be? Something plugged?
October 20, 2014
Problem solved… spider had made it’s home in the orfice. Every time I turned the burner on, the pressure of the gas would push the spider against the orfice hole causing only partial gas getting through to the burner resulting in a small blue flame.
Cleaned the spider out and now works like new again.
October 20, 2014
Thanks to the good help on the side…. The previous owner hooked the thermostat lead to the wrong post.
October 25, 2014
I have a Heat n Glo 6000GDVFL s/n32010 with a Roberstshaw-Grayson adjustable gas valve. It is a model 7000-5 with a thermocoupler as well as a thermopile generator. Pilot will not stay on.Thermopile tested holding pilot in lit postion, swithc off overload on multimeter set at 300. swtich on drop into the 190 range. Thermocouple it at 22+ as tested with pilot held in and disconnected from valve.
I shut down in the summer and restart in the winter. I have serviced it with the exception of the flue.I can feel cold air coming into the burn chamber from the flue. It had a bees nest in it and will remove debris after kill earlier this fall.
Thermodisc give me OL oh ohms. jumped it out as well and nothing
Love to make sure it is the gas valve.
November 12, 2014
Sounds like a bad valve. I would try an ohms test on it to see what it reads.
November 24, 2014
First things first – thanks so much for putting all these resources together!
I went to turn the fireplace on this season but the main burner does not fully come on. Hoping you can point me in the right direction:
Pilot lights easily and stays lit. I tested the thermopile voltage and its .600V. When I turn the switch on the voltage drops to .298V. The main burner takes a second or two to light but when it does the flame is very low, and the main burner only lights half way around, almost as if there isn’t very much gas coming out. I bypassed the switch to make sure that wasn’t the issue and had the same result. I took the burner out, cleaned and inspected it and found no blockages. I inspected and cleaned the gas orifice and it was not blocked or dirty. No improvement after all this.
My fireplace has the SIT 820 -resistance across TP and TH is 2.5. I’m confused! What should I check next?
November 25, 2014
Check your burner tube and burner orifice for blockage.
It sounds like there might be a spider nest in the burner tube and/or orifice. Run a piece of wire down the orifice and tube and try to clean it out.
December 15, 2014
That did it – the wire came out with dense white web stuck to it. Now the fireplace works like new!!
Again thank-you so much for putting these resources together!
December 24, 2014
i have a gas fireplace that i dont think has been used in years. the pilot works fine but the burner will not fire. When i connect the wall switch lead (from TH) to the screw for Tp TH the burner fires. Does this mean the switch is bad? if i connect the two wall switch leads nothing happens.
December 25, 2014
You either have a bad wall switch or there is something wrong with the wiring from the wall switch to the valve.
December 29, 2014
Your right. The valve was not wired correctly. I changed the wiring and all works well. I wonder how it got that way?
December 30, 2014
I’m having the exact same problem as Dave and was told the same thing. But, I have no idea where to clean the blockage. I can clean the burner tube, but where exactly is the “gas orifice”?
December 31, 2014
The orifice is usually brass in color and it is at the end of the burner tube. Its usually shaped like a bullet
December 31, 2014
You will need to test the voltage on your thermopile to determine the issue. Remember, the voltage should drop in half when turning it on. If it doesn’t change, check your switch, if it drops to 0, you have a short in your thermopile, if it barley drops you have a bad gas valve.
December 31, 2014
Sounds like its a bad gas valve. Make sure there are no other toggle switches/remotes/wall switches anywhere keeping it on. Then double check the thermopile voltage with the switch off and valve in the pilot position. Then turn the valve to the “on” position and see what the voltage does. If its opening up without a change in voltage, this would confirm a defect in the valve.
January 19, 2015
I have a direct vent fireplace (802.634 SIT NG valve). The pilot stays lit, but the burner ignites Intermittently, tapping the valve gently will get it going most times – then it stays lit. The voltage from the thermistor is ~340mV, I am almost sure that the valve is on the way out … your thoughts?
January 20, 2015
Check the Thermopile voltage with the wall switch off and also when its on. The voltage should drop roughly in half when it turns on. If it doesn’t drop at all, check your switch. If it drops to nothing that is a bad thermopile. If it barely drops that would indicate a bad valve.
January 20, 2015
Try going here: http://www.robertshawtstats.com/spaw2/SiteContent/Files/FAQ/ControlTips-MillivoltSystems.pdf
It provides more ways to check the gas valve.
Otherwise I would say if the pilot flame looks good, chances are it is a bad thermocouple.
May 1, 2015
Hello there, and thank you for sharing your knowledge. My pilot is good, and replace wall switch … It’s not those. When I was checking on my meter, the minute I touched the TPTH and the TH leads it fired right up, however it died just as fast when I pulled them off. I did this no less then 10 times, each same result. What could that mean? Thank you again
May 1, 2015
Then it must be something in your wiring. The switch might be okay but by touching these terminals together you are bypassing the wall switch and all of its wiring. First make sure there is not a little toggle switch somewhere near the valve that the wall switch runs through. This could be turned off.
September 26, 2015
What an unreal resource! Thanks so much. I’ve read this site over and can’t seem to pinpoint my issue. I light my pilot light just fine, then I light the burner just fine, but as soon as the the burner ignites, the pilot light goes out, then the burner wafts a bit and goes out a little later.
After reading reading the site, I assumed this was a ventilation issue. To test, I cracked the glass open, and the whole system worked great! So I assumed it was definitely a venting issue, but I’ve gone through the whole vent system and it’s wide open (goes up 4 feet vertically, then 2 feet horizontal into a chimney with a simpson chimney adapter, followed by 8 vertical feet to the termination piece).
(It should be noted that I am installing a used stove that was working great in a similar scenario in a different home.)
I did another test where I put a horizontal style termination piece 2 feet above the stove, and it still has the same behavior… here’s a video: https://youtu.be/540VL21rw4I
Please help! Thank you.
October 24, 2015
This looks like the fireplace is starving for air. The ghosting flame indicates that it is not getting enough oxygen, or its not able to expel the exhaust. If there is not blockage in the chimney vent, perhaps its in the stove itself. There should be an intake underneath the burner in the back of the stove. It looks like it would be underneath the pilot light. Make sure there isn’t any insulation, debris, birds/mouse nests, ect blocking the intake. Also, take the stove pipe off the top. Make sure both the inner and outer walls are clear.
The answer is somewhere in the venting or the intake/exhaust in the stove.
January 16, 2016
my resistance on Shaw was 10.6! Guess it is bad. http://www.youneedmeback.com
January 18, 2016
I have a 20 year old superior direct vent fireplace that has never worked correctly. When the fireplace is turned on it will operate properly for approx 3 minutes then the valve and pilot will shut off. I have replaced the thermocouple and robertshaw valve. The odd part is sometimes it will operate for hours. On the verge of tearing it out.
January 19, 2016
What happens before the fireplace goes out? Can you see the pilot flame pulling away from the thermocouple? You could try making a shield out of sheet metal to help protect the pilot from excessive draft. Does the main burner flame turn really blue and burn in the air?
February 8, 2017
You have a faulty main control valve that should be replaced
November 18, 2017
I would start by making sure the conversion was done properly. Make sure the correct kit was used and that the pilot orifice was changed. Does the pilot flame look small and weak?
February 19, 2018
Remember, the pilot light will stay burning because of the thermocouple (not the thermopile). Try to think of these as two separate things. If your pilot light stays lit but the remote control will not work, check to make sure the remote control receiver has fresh batteries in it (if it takes batteries) and that the remote control receiver is connected to the “TH” and “TP/TH” terminals on the valve. Also, make sure the remote control receiver is in the “remote” position.
February 19, 2018
Make sure that the only thing connected to your valve is the thermopile wires (there should only be two wires connected to the terminals). If you are still experiencing issues, then most likely you valve is defective. You can confirm this by following the testing your control valve troubleshooting guide: https://www.mygasfireplacerepair.com/2013/11/how-to-test-your-main-control-valve/
February 19, 2018
As far as testing the original remote control receiver, you would have to follow fire-parts “testing the switch circuit” tutorial: https://www.youtube.com/watch?v=G7OvSiUTof0
If the remote control goes bad, there is a way to wire it a wall switch or toggle switch to your stove. Please refer to page 37 in the owners manual on how to do this: https://valorfireplaces.com/media/Generic%20Title%20PDF%20manuals/English/MF28-I%20English%20manual.pdf
February 19, 2018
Try attaching a picture. If you have a SIT820 valve, this would most likely be a lead to a white plastic housing with a metal contact where the thermocouple would connect to. But its hard to say without a picture.