My HSU75NG MR. Heater (Big Maxx) will not start on its own. It purges fine ,calls for heat fine, gas flows fine; BUT there is no spark from the Electrode Igniter. Which I have replaced. The odd thing is when I use a torch to ignite the gas the unit fires right up and THEN the Electrode Igniter starts to ARC. with the new igniter the spark seems to be stronger. But the unit will not fire up without the use of a external source of ignition. I see by the parts list # 33 a Capacitor starter( which is not shown in the schematic)could this be what is not working? Also where is it located and what does it look like. Someone suggested the ignition module. What does it look like, where is it located and what is the Parts number. I really am glad that there is this help available.
The capacitor in that unit is for starting the motor that drives the blower fan. It has no impact on the ignition of the gas burner. On the control board, there is a light that should be flashing, can you tell us how many times it is flashing?
I had this happen to me also. It would try to restart 3 times then stay off. I checked everything. Found nothing wrong. Then it started restarting the blower fan every 5-10 seconds, then shuts off and repeats till i killed power. But after I started tapping on all the parts with the handle of a screw driver. It started working again. Couple months after that, it won't restart, no error code(blinking light is normal) I touched the yellow/green wire lightly, then everything fired up on its own. But then stops working after couple days. So I checked the wire connections. And re-wired the ground wire. Still happens and still looking for suggestions. Down to last resort- holy water.
SOURCE: Mr. Heater Big Maxx 75,000 BTU Heater will not
Is the circuit board giving you a blinking error code?
On a call for heat, the 24 volt thermostat sends a signal to the control module. The control module will indicate a call for heat with a light on the control either blinking or remain solid depending upon model. The inducer (exhaust) blower will purge all gasses from the furnace and pressurize a pressure switch. Once the pressure switch tells the module to continue, the electronic ignition will energize and send 120 volts to the igniter. The igniter will glow and you will be able to see it if viewed thru the small inspection port. Once the igniter gets hot enough, it sends a signal to the module opening up the gas valve (24 volts). Either a pilot will come on or the burner tube will ignite then spread the flame to all burners. Lastly a safety sensor will be looking for a certain temperature within a few seconds and the furnace will continue to operate and the room air blower will turn on in a minute or two.
What could go wrong? The unit will not run if there is no signal from the thermostat (bad thermostat or broken wire), the control module does not sense a signal from the thermostat (bad control), the inducer does not energize (bad motor), the pressure switch does not close (blocked vent piping, bad switch, plugged condensate hose), the igniter does not energize (bad control, bad igniter), the gas valve does not open or there is no gas (bad gas valve, broken wire, no gas), the pilot does not light (dirty pilot), the burner does not light (bad burner, plugged orifice, not enough combustion air), the flame does not spread to each burner (bad flame spreader, dirty flame spreader, more bad burners), the flame safety sensor does not detect flame (dirty or bad flame spreader, bad flame sensor, broken wire, bad control), or the room air blower does not energize (bad fan motor, bad control).
SOURCE: Heater will not light. When the T-Stat calls for
Are you sure that your gas supply is strong enough, and that being said is there an in line regulator on your installation? You need gas pressure along with volume to burn properly. The itself sounds fine it is going thru all of its system checks then shutting down. You need someone with a set of gauges and check gas line pressure then check past the regulator and again check the pressures. It could be as simple as opening the regulator up slightly or as costly as replacing the line with a bigger one to support the heater. Make sure that you have purged the line good, and I would do this at the dirt leg in the supply or as close to the heater as possible.
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