Gas Fireplace Problem

[Rob5]

I have a Majestic G2000adi gas fireplace.  The flame is acting like there is a failing flame sensor.  That is, it lights and then goes out in a few minutes or hours.  Unfortunately the company was bought in 2008 and the new owners do not support the fireplace with parts.

I think that the flame sensor is a direct sense using flame rectification via the hot surface ignitor.  There is a bracked just over the HSI that is corroded and worn away.  As I understand it an AC current is sent through the HSI and the flame conducts current to ground, maybe through this bracket, verifying the pretense of the flame.  I think that the corroded bracket is the ground for this system.  Is this correct?  There are no other devices or wires anywhere near the burner.

I cannot find a source for the bracket.  What can I do to fix this?

I got this fireplace with HSI in place of a pilot light because of regulations to save gas.  So far I have had to buy a generator to allow for emergency heat and now I am facing a $3000 new fireplace if I cannot fix this.  Help!

[Daveb1972]

Usually when they use the HSI as the flame sensor they rely on a nearby ground source to complete the circuit with the flame. They measure DC microamps  on the line. The flame works like a diode to rectify AC voltage on the HSI line, and measuring the amps they know if the flame is real, or if the HSI is grounded or open.

So, the shield on the HSI isn't usually where the flame completes the circuit. Often its through the burner itself, or in some cases they install a ground rod near the HSI.

 

Considering the above, there is yet another idiosynchrocy (sp?) at play. The HSI is usually made of one of two materials, Silicon Nitride, or Silicon Carbide. The more common is the SiC type, and it will appear slightly sparkly and are VERY brittle. If its a 120volt igniter it is most likely a SiC.

 

The igniters have a life cycle too, and even when they look okay, they may be failing. The only accurate test of an HSI is by testing the resistance while cool/cold. With power disconnected, connect ohmmeter across HSI terminals (disconnected from controller) resistance should be around 80ohms. if 100ohms or greater (even 95 or more) HSI is failing and should be replaced.

This is where the good news comes in.... depending on the exact model HSI you might also get a bracket with the replacement unit. I suggest you test the HSI then if it fails pull it and send a photo of the HSI. Photo before you pull it is cool also. I might be able to help you source a replacement part.

 

 

For additional diagnostic info.... Normally flame rectification takes the first 4 seconds of main valve flow, then the control cuts out and a restart is attempted. I'm not convinced that's what you have here, but the HSI might be getting old and intermittent.

 

Please send as many detailed photos of the HSI, Control Box, and data plates/tags so I can further assist you.

[Rob5]

Dave,

Thank you for your reply.  I have been to three fireplace stores and several internet parts vendors and you are the first to understand the question.

My fireplace is a Majestic G2000 adi,, serial number 226000631.  The ignitor part number is 75-92-105 and the bracket installed over it is 39-94-123.  I will attach several pictures showing these parts.

The tag on the HSI says 75-92-105 and Norton 201 W.  I measured the resistance of the HSI at about 75-85 ohms.  I got different readings depending on my ability to connect to the small male connectors inside the plug.

While I had the parts out I cleaned them with steel wool.  Maybe that will help.  The HSI looks like SiC, gray with sparkles.

This fireplace was installed in 1994.  The contractor told me that it could not have a pilot light because of recent laws outlawing them in Decorative Fire Appliances.  There is a tag inside saying that it is a decorative appliance  not to be used for heating.  That is odd since it came with a blower to move heat to the room and it is rated at 45,000 BTU, about half of my furnace's rating if I remember correctly.

I will have to figure out how to post pics.  I will do that when I can.

Thanks for your help.

Rob

[applianceman18007260692]

This seems to me to be like one of them jet heaters they sell at home depot. The blower comes on the ignitor glows and the flame ignite and as long as the flame is on the ignitor sends back a signal to the control that the heat is on and she stays on. You must have a weak ignitor or a loose connection.

[applianceman18007260692]

clean up around the ignitor as best ye can without breaking it. make sure the flame out the burner is stayin in the glow thingy

 

 

[Rob5]

http://s1052.photobucket.com/user/wrgriswold/library/

I think that I may have managed to insert pictures. 

[Rob5]

Well, at least I got the link in.  The first four pictures are the ones to look at.  The others are of a blow out I had on my trailer.

[applianceman18007260692]

That looks like the kind of glow bar you see on gas dryers and on gas stoves. Now since their is no sensor associated with this picture then I assume it has a slow opening gas valve a glow bar and a temp control. The way it works is the glow bar (ignitor thingy) has to drop in resistance so that it can allow the gas valve to open slowly and let gas out to the burner. I would check the ignitor to see f it draws enough amps to open the gas safety valve. One way to do it is visually look at the ignitor while it is on. It should be VERY bright blinding and if it is orange dim orange burnt orange its weak and not opening the gas safety valve. if it ain't glowing at all you either ain't paid the electric bill or the control hay took a dump.

[applianceman18007260692]

another way to know if it is the ignitor is to bump the gas valve at the base of the burner while the glow bar thingy is on and see if she fires off if she do fire off you need a newer better glow thangy.

 

[applianceman18007260692]

one thang you DONT want to do is power up the gas safety valve without the glow thing in line with it all that will do is cook the innards of the valve which aint nothing but a flat thin metal flap with a piece of wire wrapped around it. As the ignitor glows hotter and hotter this causes the flap to curve from the voltage being pushed around it through a tine filament wire. as along as the voltage is all propah the flap stays open the burner remains burning the whole shebang keeps on purring along until... the wall thermostat or some kind of control kills the power to the system then the small filament slowly cools down and the flap shuts back closed and no mo fire. pretty clever aint it?

[Rob5]

Applianceman,

Thanks for your reply.  My fireplace has no trouble lighting, just staying lit.  The ignitor is not expensive and I would just replace it if I was sure to get the right one.  I worry about the metal piece with the holes in it that is installed over the ignitor, that I cannot find.  It may be there to ensure gas is around the ignitor to be lit or as a source of ground for the sensor function.

Thanks again.

[Hiroshi]

that appears to be a flat dryer igniter... that would operate in conjunction with a radiant sensor when in a dryer- it isn't exact amperage draw for use with a safety valve. You should try to include a shot of the valve and the rest of the mechanicals under the unit- so we can figure out what you actually need (or what would safely work)

the metal cover is the least of your concerns, the electrical properties of the system are more important to keep the building from burning down!

[Rhubarb Tau]

2nd the call for more pics. I worked on gas fireplaces (and pellet stoves, various "hearth appliances") for ~6 years, and I never saw any pilot/flame-proving hardware anything like what I've since run into in the broader kitchen/laundry appliance world. Most non-standing pilot units used flame rectification, usually handled by a module of the same make as the gas valve. RobertShaw, SIT and Dexen come to mind, though it's been a bit.

Without any further info, and speculating wildly... I agree, sounds like a flame-proving issue. Might sanity-check it by timing the delay between call-for-heat  (switch or thermostat closing) and the second that the valve shuts, and compare against the timeout between switch closure and shutoff with gas shut off at the shutoff valve.

If that pencils similarly, might start by wiggling (or applying contact cleaner) to whatever terminal the sense electrode hooks up to. 

 

[Rob5]

Here are two more pictures.  The first one is the adi controller and the second is the valve.

http://s1052.photobucket.com/user/wrgriswold/library/

I hope these help.  If not let me know what pics will.

My goal is to replace the HSI and I need to find the appropriate part.  I am competent to replace that part but I do not want to get into the controller or valve.  Local techs seem to know less than me.

 

[Rhubarb Tau]

If you just want to try the ignitor, heres a subbed part:

https://www.theignitorstore.com/product/41402_furnace_igniter

If you wanted to diagnose down before ordering parts, you could try ohming out the valve or looking for valve output from the control box during a failure. Wait until the burner shuts off on it's own, then take some measurements to see where in the switch-control-valve chain it's cutting out.

You might also check if the unit has a high-limit switch that could be cutting out, and verify that the wall switch, thermostat or remote is closing with low resistance.

If no luck, check and see if there's a schematic label somewhere in the valve cavity.

[Rob5]

Thanks.  I ordered that part.  I will report back after it is installed.

[Rob5]

The part has arrived.  It seems to be exactly like the old one with the exception that the old one had a mesh like insulation tube sleeve on the first 8" or so of the leads.  I put the insulation on the new part and installed it.  The fireplace ran for an hour with no problems.  The real test will be next fall when cold weather returns.

So it seems that the flame sensor function was failing and the ignitor still worked.

Thanks to all of you for your help.