Mr Heater Big Maxx won't ignite

[Mecnic]

My big maxx worked perfectly last year. It is hooked up to natural gas. When the t-stat is turned on and up it will not operate the inducer motor, nor try to complete the ignition sequence. It flashes a code 2 which indicates system lockout, inability to maintain a flame. Though it never reaches the point in the process in which it would turn the gas valve on or the igniter. All of my tests are with a fluke dvom

What I know
1 it has 120v, it has gas to it, it has 27v out of the transformer to the board.
2 none of the limit switches are bad, jumped all of them.
3 the thermostat is closing the circuit.
4 the circuit board isn't the issue. I installed a new one with the same results.
5 The flame sensor is clean
6 The pressure switch is closing the circuit when I apply pressure.
7 it will set this code every time you power the unit off and back on without ever turning on the inducer.
8 all connections are free of dust dirt and such. and feel secure

What I don't know
1 how to test the flame sensor
2 does the controller do a circuit check prior to step one in the sequence?
3 What the heck else to test?

I want to fix this heater now more so for the challenge, and would appreciate any input.

 

[Showkey]

The inducer fan must run first.........
The pressure switch confirms draft ........
Ignition occurs as Gas valve opens and flame sensor verification the burner is lit

So sounds like your inducer fan does not run.........verify fan turns and runs, verify power to the the fan.

Flame sensor faults cause the process to stop right after burner lites for 2-5 seconds. That does not sound like your problem.

 

[Mecnic]

Yes I agree that the induce must run first, it is free and will run if I unplug a limit switch while it is the lock out state.

Here is my thought, The controller is doing a circuit check prior to starting the inducer. Checking that the circuits are pulled up or down in the rest state, if all is ok then it will start the sequence, if not then it flashes a code. I think this because if lets say the flame sensor which changes resistance when heated up, is at a operating value prior to a flame being present then it would continue to hold the gas valve open without a flame.

But I could be over thinking it.

 

[Showkey]

The flame sensor is only in play after ignition. It sends millivolt signal when the flame is present.
The only other possible precheck might be the pressure sensor has to be open or closed at the start and the fan blower trips it the other way.

 

[D45]

You sure the blade fuse on the panel is not popped?

 

[Mecnic]

D45 I am certain the fuse is good.

 

[Mecnic]

Showkey I can see the change in the voltage output 0 to 24v of the pressure switch when I apply a slight pressure on the hose. So I can't think that this is the problem.

 

[Showkey]

The only other guess at this point is one or more of the roll out or other over heat switches is tripped or failed. That would stop the board from resetting.

Or.......a wiring or device short took the old board out and the new board out as well.

Or something simple got over looked ???????? Corrosion on connector, broken wire.

Unfortunately Buying new parts is not cheap, a new heater is $399. My board fried , my furnace was rusty sticking, $200 in parts in a $400 heater might not make sense.

 

[D45]

Can you make a jumper wire and bypass a roll out switch, one at a time?

https://www.garagejournal.com/forum/showthread.php?t=374715&highlight=rollout

 

[klassenl]

Some of them do a check for proper open/close of limits. That way it's gets very difficult to manually over ride the safety's.

If you need to jump the limits you have to wait until the proper time in the sequence.

 

[Done That]

Verify good ground, its critical for flame sense circuit.
You test a flame sensor by unplugging from control and putting your meter in-line with it and read micro amps. Sure there's a youtube video you can follow.

 

[Mecnic]

This one is fixed, thank you for all the replies and sanity checks.
We all believe that the inducer coming on is step 1 of the sequence. But in fact it isn't. So what is step one of the controller, I have found that it does circuit checks prior to the inducer coming on. And this is where my heater would fail and flash code 2. The control board looks at the limit switches, the flame sensor and the gas valve circuits 1st.

Mine was sending 14v to the gas valve and expecting to see return voltage of less than that and didn't. So it failed. They way that I found the issue was I could ohm the gas valve and get a 1.4 mega ohm reading but when I reversed the leads I got an open circuit. It should be close both ways. I removed the gas valve circuit board and didn't a bit of inspecting. It is a very simple board, 4 diodes is pretty much it. I tested the diodes and found one that was open. Since I had replaced the control board I located one in the board and installed it in the gas valve board. Reinstalled and viola, the inducer kicked on finished the sequence and now I have heat.

Sorry for the long story to sum it up but hopefully it will help one of us in the future.

 

[The Cobbler]

nice find & repair . thanks for sharing

 

[Junkman]

I bought a Bix Maxx heater about 10 or 12 years ago, and it didn't work out of the box. I contacted their technical service department, and they kept sending me replacement parts. Ultimately warm weather came, and I didn't need the heater, so I left it for "next season", but never got around to doing any work on it. The boxes of parts are still on the top of the heater. My problem was (is) that 2 or 3 of the logs would light at the bottom, and they wouldn't light those further up. Can anyone help me with this? My unit is set up for propane, and I have propane appliances throughout the home, so I know it isn't pressure related, because there are 4 large tanks installed. Thanks

 

[spudley]

So as the burners light from the bottom, the flame should spread to the next burner up.

Remove each spreader and make sure they're open. D45 has an extensive thread on an older model failure where the top spreader was tripping the flame roll out sensor. He pinched it shut and his problem was fixed.

Sounds like you have the opposite issue in that your spreaders are not open enough.

It also could be pressure related as the gas valve could be set incorrectly. Check it with a manometer.

 

[spudley]

This one is fixed, thank you for all the replies and sanity checks.
We all believe that the inducer coming on is step 1 of the sequence. But in fact it isn't. So what is step one of the controller, I have found that it does circuit checks prior to the inducer coming on. And this is where my heater would fail and flash code 2. The control board looks at the limit switches, the flame sensor and the gas valve circuits 1st.

Mine was sending 14v to the gas valve and expecting to see return voltage of less than that and didn't. So it failed. They way that I found the issue was I could ohm the gas valve and get a 1.4 mega ohm reading but when I reversed the leads I got an open circuit. It should be close both ways. I removed the gas valve circuit board and didn't a bit of inspecting. It is a very simple board, 4 diodes is pretty much it. I tested the diodes and found one that was open. Since I had replaced the control board I located one in the board and installed it in the gas valve board. Reinstalled and viola, the inducer kicked on finished the sequence and now I have heat.

Sorry for the long story to sum it up but hopefully it will help one of us in the future.

That's a pretty good fix mon ami. I'll give you 4 GJ stars for that.

How'd you get those goofy screws out?

 

[Mecnic]

I am a master auto tech by trade so I went to my tool box and got the tamper proof torx socket for them.

 

[spudley]

I am a master auto tech by trade so I went to my tool box and got the tamper proof torx socket for them.

Then you only get 3 1/2 stars. Oh hell you get 4 cause you scavenged the diodes from the old board.

 

[TractorJeff]

He gets 4 Stars for telling us what and how it should work, THEN telling us how to troubleshoot and fix it!

 

[spudley]

He gets 4 Stars for telling us what and how it should work, THEN telling us how to troubleshoot and fix it!

Yep. Not too many mere mortals popping open gas valves and sniffing out bad diodes. Wish he was my neighbor.