[justplumducky]

M1B series Miller furnace with Integrated Furnace Control board. Pic below.

Igniter w/flame sense glows to full brightness (30 sec warm-up period) after normal combustion air motor purge cycle, then a click from the board produces 24vac at gas valve, but only momentarily (1-second or less). Gas valve does not open.. no usual heavier relay clicking sound coming from the gas valve. At the same instant the 24v only "flashes" on my meter's LCD, the igniter powers off. No 6-seconds ignition trial time.

Repeats same two more times, then lockout. My guess is a bad IFC board (relay), because I had something very similar to this happen before (posted it in here) and you agreed with my diagnosis of bad control board, which it is was. However, this igniter w/flame sense is new to me and its resistance measured 174 ohms with its pigtails disconnected from the board leads that feed it voltage. I'm still thinking the board is bad, but also wondering about the combination igniter/flame sensor. Or maybe a bad igniter w/flame sense could shut down ignition attempts? I'm trying to find normal ohms range online for this igniter. No luck yet. Normal ohms range?

Not sure about the mounting part, but the round, spiral barrel (the element part) of the igniter in pic below is the same as the one on the furnace.

Problem is, I'm not sure how long after an initial ignition attempt, or two, it was when I checked its resistance. Maybe it was still warm which I'm guessing would yield higher resistance.

The pressure switch is lying down on upper shelf cuz I was checking it out.

Returning to the job on Monday and since supplier is not far from job, thinking I should check cold igniter ohms first, then pick one up if need be, along with a board. Good game plan? Bad game plan?

 

[yuri]

Probably the relay on the board for the gas valve is weak and not holding the contact closed. Doubt it is the igniter. I would replace the board. Check the igniter cold and record the reading in a notebook for future reference. I have a Porta-file when different sections for different brands. Office Depot has them or Staples or WMart. Crappy furnace IMO as those inducer fans get weak and are plastic.

 

[justplumducky]

Probably the relay on the board for the gas valve is weak and not holding the contact closed. Doubt it is the igniter. I would replace the board. Check the igniter cold and record the reading in a notebook for future reference. I have a Porta-file when different sections for different brands. Office Depot has them or Staples or WMart. Crappy furnace IMO as those inducer fans get weak and are plastic.

Watched a video about a Robertshaw 780 HSI Ignition Control used on an 80%-er, and it caused a similar problem I've posted here, because it didn't have a good ground from the control to chassis. However, the control did have a ground terminal on it.

I was about to ask if there was any possibility my problem could be a ground issue (board to chassis ground, assuming furnace cabinet/chassis is properly grounded), but then I noticed there's no GND terminal on my IFC board in question (pic below). Maybe any necessary grounding (if necessary) is accomplished via the 24v C terminal on the board? This IFC board apparently just sits on the stand-off pegs (or whatever they're called), not screwed to the chassis.

But then again, if that were a possible issue, you probably would have mentioned it already.

 

[beenthere]

If the gas valve is getting 24 volts, it should open. Valve may have a short in it, over loading the boards relay, and causing the quick ignition failure cycle.

Might want to see if it opens when you run 24 volts to it directly.

 

[justplumducky]

If the gas valve is getting 24 volts, it should open. Valve may have a short in it, over loading the boards relay, and causing the quick ignition failure cycle.

Might want to see if it opens when you run 24 volts to it directly.

Will do that, thx... but wouldn't a short in valve blow the board's 3A fuse, or does that depend on the intensity of the short?

Yuri, I'll comment a bit later on your Port-A-File suggestion, thx. I like the one with the handle. Or maybe those are both the same unit. I keep call reports in files at home (problems/things to check for/solutions,), but better to have it in the truck for sure, and I will organize them according to furnace models... also according to customer address probably so I can look-up & review reports after getting a phone call for from a particular address. Have also been assembling a thick D-ring binder with parts illustrations (exploded diagrams with parts lists, per model series) and other info. Only have about five home so far (non-mobile-type, but for mobile homes/RV's and whatever other applications for downflow furnaces, I recently found a great site for parts illustrations & lists per brand & model number. For anyone else this might help:

http://mobilehomedepotmi.com/

Well, looks like I'm commenting on it now! ("I'll comment a bit later on your Port-A-File suggestion")

 

[justplumducky]

M1B series Miller furnace with Integrated Furnace Control board. Pic below.

I'm not at all sure, now, that this is an M1B Series furnace... Maybe, maybe not, but the only parts illustration & list that had the correct parts illustration and part numbers for this board and other components, was the M1M parts illustration and list. Anyone interested can check out the various model series listings info at www.mobilehomedepotmi.com (Heating & Cooling link, far right, then "Furnaces" far left), as mentioned in last post.

 

[yuri]

I have never had a shorted valve like Been~ mentioned but it is a very small remote possibility. 99.9% of the time it is a bad relay on the board. I would try a new board. You can go directly from the 24 volt transformer to the valve but you better have a friggin red hot igniter and get the timing right or you may get a BIG bang. Very experienced techs like BT and myself might try it. I would replace the board as it is safer for you. Sometimes you have to just try change parts rather than theorise your way thru it.

C is grounded as the secondary of the transformer is grounded. If the board is not properly grounded then the flame signal from the sensor will not make it's way back to the board properly. Has nothing to do with the board/transformer/C terminal. Some high end boards for modulating furnaces etc check the grounding and polarity but you are not working on one. Some boards have a brass grommet on them and a mounting screw touches it and goes into the sheet metal to ground them. Others use a wire.

There were a few Robertshaw boards that used the igniter as a flame sensor and do not have a flame sensor and wire. Coleman used them and possibly Miller. Mostly obsolete and I don't know how to describe how it worked. Coleman got rid of it and had a conversion kit back to a seperate flame sensor.

 

[justplumducky]

I have never had a shorted valve like Been~ mentioned but it is a very small remote possibility. 99.9% of the time it is a bad relay on the board. I would try a new board. You can go directly from the 24 volt transformer to the valve but you better have a friggin red hot igniter and get the timing right or you may get a BIG bang. Very experienced techs like BT and myself might try it. I would replace the board as it is safer for you. Sometimes you have to just try change parts rather than theorise your way thru it.

C is grounded as the secondary of the transformer is grounded. If the board is not properly grounded then the flame signal from the sensor will not make it's way back to the board properly. Has nothing to do with the board/transformer/C terminal. Some high end boards for modulating furnaces etc check the grounding and polarity but you are not working on one. Some boards have a brass grommet on them and a mounting screw touches it and goes into the sheet metal to ground them. Others use a wire.

There were a few Robertshaw boards that used the igniter as a flame sensor and do not have a flame sensor and wire. Coleman used them and possibly Miller. Mostly obsolete and I don't know how to describe how it worked. Coleman got rid of it and had a conversion kit back to a seperate flame sensor.

Still at home, not going to this job till earlier afternoon. If board has no apparent mounting screw that grounds it to the sheet metal cabinet, then the grounding would have to be accomplished via a wire feeding into one of the molex connectors it seems, correct?

After watching the timing of this sequence Saturday more than a couple times, I believe I could get the timing right. Not saying, yet, that I won't just change the board (was actually planning on taking a new board to this job this afternoon), but what about shutting off the gas SOV, then letting the ignitor get fully red hot (watched it heat to full red hot from one end to the other a few times Satruday - spiral wound ignitor is in full view via the inspection window), then attach the jumper wires to valve. When this valve comes on, it makes an obvious heavy & loud click, but maybe I don't even have to have a call for heat?... maybe just jump a separate 24vac source to the valve? I have such a testing device with toggle switch, and alternate spring loaded toggle switch (forget what you call that at the moment)... well, "momentary switch" maybe. Actually, the momentary one is not a toggle switch, but a momentary push-button type.

This ignitor is definitely a combination ignitor and flame sensor... no separate flame sensor on this unit.

Always grateful for your "cautions." I learn from them.

 

[beenthere]

Sometimes I just put my manometer on the valve/manifold, and energize the valve directly off the transformer without a call for heat. If I read pressure, the valve is good and opening. If no pressure, either the valve is done for, or no gas to it.

 

[yuri]

If it is a non flame sensor setup then I don't know how it senses the flame thru the ignitor. May have some timing circuit thru the Robertshaw board and then uses the igniter with DC volts. Nobody seems to know other than it sukks. If Miller has a retofit kit to install a flame sensor and newer Robertshaw board I would do that.

 

[beenthere]

The board has a slight delay between HSI de-energization, and flame sensing/uA reading.

Works very similar to a spark ignition system that senses internally. Which just means it uses the spark ignitor as a flame sensor.

 

[yuri]

Kinda impossible to toubleshoot plus those nitride HSIs get carbon schmutz or dirty gray after awhile which may add resistance.

 

[beenthere]

I've changed a good number of HSIs that would ignite teh gas. But didn't allow enough of a uA pass back through for teh board.

 

[yuri]

Fortunately I only ran into 3-4 and they were Coleman resi furnaces not trailers. All of them have been replaced and I rarely do trailers. Electric is what 95% of trailers use where I am. I did a retrofit on a Coleman with the add on flame sensor and new board.

 

[justplumducky]

I took a new board to the job, checked ignitor/flame sensor ohms soon as I got there (cold igniter).... over 219 ohms. Supply house counter sales rep. told me while I was picking up the new board (before I went to job) that anything over 80 ohms is a bad igniter, but I remember checking an igniter/different job previously (not a combo igniter/flame sensor unit however), and it was 90 ohms and working well.

Didn't take a new igniter with me to job, so left it in to see what would happen after installing new board. Started it up with new board installed and gas valve opened consistently. I'm saying "consistently" because after it started up successfully, it starts short cycling while in the process of raising the room temp to set point. This furnace was not run since Saturday afternoon. I have seen standing pilot furnaces (trailers) do the short cycling thing because they were being started up after long periods of not being run in cold weather. Don't remember the exact reason without checking some notes, but I believe that had something to do with the furnace being so cold. They would run a little longer with each progressive cycle toward room temp, until it finally ran/cycled with normal frequency.

So I figured maybe this board-controlled furnace was doing the same thing (short cycling while warming up), but then I checked the anticipator setting on the very inexpensive mechanical heat/cool tstat customer had installed ($15.00). Was set at .13/lowest setting, and the protective cardboard insert hadn't been removed either. So I bumped it up two different times, ending at .4. Didn't remember at the time where to set the anticipator (had a conversation in here about this, which I will have to dig up and print), but remembered that the owner's manual (or installation instructions) for this furnace said it could be set per the amp rating on the gas valve (maybe one unit higher than amp rating). This wasn't one the usual gas valves I'm used to seeing that have the specs on the front side of valve (pic below). In fact, this valve looked nothing like the ones I've been seeing (couldn't find any specs on it). Don't see that many (only a part-timer), but still...

Could not find or at least see it, even with a mirror if indeed it was there on the back side of valve, so I just took a shot at it twice, stopping at .4 and it increased its run time from about 2 min or less, to about 6 or 7 minutes. Then the flame drops out, but restarts while unit is still on its way up to room temp. This is normal? Going back one more time tomorrow, and possibly change the tstat to a digital unit. Digital would have automatic anticipator function, yes?

 

[beenthere]

Most digitals will have CPH. Cycles Per Hour. 3 is a good CPH for most furnaces and boilers.

 

[yuri]

Take the W wire off the tstat at the board and wrap it 10X around the jaws of your amp meter or put it in series with a digital meter and get the reading. Have to divide by 10 on the clamp meter unless it is very sensitive and can read it with 1 wrap. Setting it for the amps rating on the valve works if you can read it. Sometimes the furnace can cycle on the limit control if it runs for a long time and airflow is borderline.

 

[justplumducky]

I'm not at all sure, now, that this is an M1B Series furnace... Maybe, maybe not, but the only parts illustration & list that had the correct parts illustration and part numbers for this board and other components, was the M1M parts illustration and list. Anyone interested can check out the various model series listings info at www.mobilehomedepotmi.com (Heating & Cooling link, far right, then "Furnaces" far left), as mentioned in last post.

Checked on the model number while at the job today, and it is not M1B 056A BW, but is M1MB-056 A-BW as suspected.

The M1 Series Furnaces Technical Specs at http://www.millerfurnace.com/Literature/713a.pdf
shows at the bottom of SPECIFICATIONS chart, that the Normal Anticipator Setting is 0.4, so if I don't end up replacing their mechanical tstat, will leave it where I "took a shot at it", which was also 0.4 and see how it's going tomorrow when I go back. Maybe put the W wire at the board in series with meter as suggested, and see how it compares to .4

 

[justplumducky]

For future reference, would a short-circuited gas valve (voltage sent to valve appearing on my meter display only for 1/2 second before disappearing) show up during a continuity test on the valve?

We replaced a gas valve a while back with new, but too bad I ended up throwing it out, instead of experimenting with it. I did take it apart to have a look-see, but now I have that previously mentioned 24vac testing device.

 

[yuri]

I don't know, never had one short.