Question about Mr. Heater MHU45NG

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Mr. heater model mhu45 combustion air blower will not start. len on circ uit board blinkiing s times. cleaned flu ahd vent exshaut.

Checked pressure switch and is closed prior to trying to start, still get pressure open led signsl and no cab startup.

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On your heater, does it tell you a fault code for the number of blinks?

If you have cycled the power to the unit already, the fault code should have cleared. If the fault code cleared and then came back, sounds like either a issue the blower motor being shot, or a relay in between the ignition controller and or the ignition control is bad, not making the heater do anything.

Posted on Nov 20, 2013

  • 1 more comment 
  • robert browning
    robert browning Nov 21, 2013

    t hanks for the feedback. either could be the cause.mr. heater thinks the control board is shot and are sending me a new one via waranty.

  • robert browning
    robert browning Nov 21, 2013

    Add a Commenti

  • robert browning
    robert browning Nov 21, 2013

    i will let you know.

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hotuna
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SOURCE: MHU 75 Model Mr. Heater

The roll out switch is a small disc shaped part about the size of a nickle. There may be more than one. anyway there is a button shaped like a small peg in the center if it, push it in and it should stay in. You may need to re examine the limit switch, because this is what it sounds like. they are rated for a set temperature, so your application may need a higher temp. A simple way to check parts like these is to by-pass them by taking the wires off the part and connecting them together. If this solves the problem, that it. My only concern is that this is a new installation, and maybe its not venting adequately or its burning up all the usable air in the room. That's why most of these parts are on the equipment.

Posted on Dec 24, 2007

  • 1015 Answers

SOURCE: I have a Big Maxx

You may very well be right because if the induced draft motor won't come on then the heatin cycle stops there. It makes me wonder about the board because of it doing the same thing even if it's not calling for heat. Thanks.

Posted on May 13, 2011

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I have a goodman furnace GMP100-4 REV B..about a year ago it was not working. The fan would start but it would not ignite. We found out we need a new ignitor and it was a good quick easy fix. Now a ye


Any light flashin on the control board? If not then look for a small fuse blown on the board. See lights a flashing count them flashes

A sampling of various failure codes on a furnace:

Read one LED flash that stays on continuously to mean your furnace has no signal coming from the thermostat and will not operate. Turn the power off and check the thermostat for improper settings or connections.

Interpret one LED flash that blinks on and off to mean your furnace has locked out because it could not ignite after three tries, and must be reset. Interrupt power to your furnace for 20 seconds or lower the thermostat so your furnace does not try to heat, then reset the thermostat to the previous setting. After one hour of lockout, your furnace will automatically reset itself and try to operate as usual.

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Read three LED flashes to mean your furnace has an open pressure switch circuit or it has an induced draft blower operating. Check the pressure switch hose of your furnace for blocks or an improper connection. Also, look for blockages in the flue, and tighten any loose wiring.

Translate four LED flashes to mean your furnace has a primary limit circuit open, possibly from loose wiring or blocked filters. Check and clean filters, tighten wiring and check the flue for blockages.

Interpret five LED flashes to mean your furnace senses a flame without a call for heat. This could be from a gas valve closing slowly or a burner flame lingering.



Read seven LED flashes as a warning of a low flame sense microamp signal. This could happen with a coated flame sensor or a lazy flame from poor gas pressure. Turn off the power and adjust the gas pressure according to the information on the rating plate.



See eight LED flashes as meaning an igniter circuit problem due to a bad igniter or an igniter connected improperly. Replace the bad igniter or check the ground wiring, making necessary corrections.



Decipher nine LED flashes to mean the high-stage pressure switch circuit will not close during a high-stage-induced draft blower operation. Your furnace may have a pinched or blocked pressure switch hose, a blocked flue or loose wiring.

Read continuous flashing on the LED to mean your furnace has a reversed polarity of 115 volts. Turn off the power and correct the wiring polarity after reviewing the wiring diagram.

Nov 29, 2011 | Goodman Heating & Cooling

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I have goodman GMP series furance the furnance and gas comes on and fires up then goes out flame sensor is good what else could be wrong


Improper ground from control to burner.
Incorrect electrical wiring, check polarity.
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A sampling of various failure codes on a furnace:

Read one LED flash that stays on continuously to mean your furnace has no signal coming from the thermostat and will not operate. Turn the power off and check the thermostat for improper settings or connections.

Interpret one LED flash that blinks on and off to mean your furnace has locked out because it could not ignite after three tries, and must be reset. Interrupt power to your furnace for 20 seconds or lower the thermostat so your furnace does not try to heat, then reset the thermostat to the previous setting. After one hour of lockout, your furnace will automatically reset itself and try to operate as usual.

Decipher two LED flashes to mean the draft blower is not working, or your furnace has a short in the pressure switch circuit. Turn off the furnace power and repair a short or replace the pressure switch.


Read three LED flashes to mean your furnace has an open pressure switch circuit or it has an induced draft blower operating. Check the pressure switch hose of your furnace for blocks or an improper connection. Also, look for blockages in the flue, and tighten any loose wiring.

Translate four LED flashes to mean your furnace has a primary limit circuit open, possibly from loose wiring or blocked filters. Check and clean filters, tighten wiring and check the flue for blockages.

Interpret five LED flashes to mean your furnace senses a flame without a call for heat. This could be from a gas valve closing slowly or a burner flame lingering.



Read seven LED flashes as a warning of a low flame sense microamp signal. This could happen with a coated flame sensor or a lazy flame from poor gas pressure. Turn off the power and adjust the gas pressure according to the information on the rating plate.



See eight LED flashes as meaning an igniter circuit problem due to a bad igniter or an igniter connected improperly. Replace the bad igniter or check the ground wiring, making necessary corrections.



Decipher nine LED flashes to mean the high-stage pressure switch circuit will not close during a high-stage-induced draft blower operation. Your furnace may have a pinched or blocked pressure switch hose, a blocked flue or loose wiring.

Read continuous flashing on the LED to mean your furnace has a reversed polarity of 115 volts. Turn off the power and correct the wiring polarity after reviewing the wiring diagram.

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I have a 50 gallon rheem direct vent natural gas heater. The pilot light goes out on an infrequent but aggravating basis. I replaced the thermocouple one time and it got better for about a year but has...


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http://waterheatertimer.org/pdf/Pilot-light-will-not-stay-lit.pdf
http://waterheatertimer.org/images/Negative-pressure.jpg
http://waterheatertimer.org/pdf/Bosch_Ventilating_tight_houses.pdf

Since pilot light goes out and can be re-lit, problem is probably not thermocouple, gas control valve, or air in gas line. But these things can factor in as contributing factors.
Problem is likely one of following or combination of following including dirty burner parts, tight house, incorrect vent lengths, negative pressure caused by other venting appliances, condensation dripping down into combustion area, and inadequate oxygen supply due to hot or closed-off room or attic location.

Gas water heaters draw air from surrounding area. If water heater is located inside house, then air has to enter home through cracks and when doors and windows are opened. Other gas appliances and vent fans also draw air from same indoor area. When other vent fans turn on, air can be drawn down the water heater vent and blow out pilot light.
Inspect combustion chamber to make sure there is no condensate water dripping down from incorrect vent that is putting out flame. If combustion chamber is dry, then close doors and windows. Turn on all vent fans and gas appliances that vent outdoors, and see if water heater pilot goes out.
Consult with plumber or product manual about proper horizontal and vertical lengths of vent pipe for your model. Have plumber clean combustion parts and inspect vent termination and check gas pressure and bleed gas line.
Add louver opening to outdoors so air can enter room where water heater is located.

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I have a Big Maxx heater that about 4 months old,and it started to act up, when I checked the circuit board I have three flashes. I removed and checked the pressure switch and that checks out fine, I get...


You may very well be right because if the induced draft motor won't come on then the heatin cycle stops there. It makes me wonder about the board because of it doing the same thing even if it's not calling for heat. Thanks.

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Suddenly not working im not sure if there even is a pilot to be lit


Goodman have troubleshooting idiot lights on the board. Look for flashes and count em.
The flash explanations are printed on the backside of the blower cover on most models.
A sampling of various failure codes on a furnace:

Read one LED flash that stays on continuously to mean your furnace has no signal coming from the thermostat and will not operate. Turn the power off and check the thermostat for improper settings or connections.

Interpret one LED flash that blinks on and off to mean your furnace has locked out because it could not ignite after three tries, and must be reset. Interrupt power to your furnace for 20 seconds or lower the thermostat so your furnace does not try to heat, then reset the thermostat to the previous setting. After one hour of lockout, your furnace will automatically reset itself and try to operate as usual.

Decipher two LED flashes to mean the draft blower is not working, or your furnace has a short in the pressure switch circuit. Turn off the furnace power and repair a short or replace the pressure switch.


Read three LED flashes to mean your furnace has an open pressure switch circuit or it has an induced draft blower operating. Check the pressure switch hose of your furnace for blocks or an improper connection. Also, look for blockages in the flue, and tighten any loose wiring.

Translate four LED flashes to mean your furnace has a primary limit circuit open, possibly from loose wiring or blocked filters. Check and clean filters, tighten wiring and check the flue for blockages.

Interpret five LED flashes to mean your furnace senses a flame without a call for heat. This could be from a gas valve closing slowly or a burner flame lingering.



Read seven LED flashes as a warning of a low flame sense microamp signal. This could happen with a coated flame sensor or a lazy flame from poor gas pressure. Turn off the power and adjust the gas pressure according to the information on the rating plate.



See eight LED flashes as meaning an igniter circuit problem due to a bad igniter or an igniter connected improperly. Replace the bad igniter or check the ground wiring, making necessary corrections.



Decipher nine LED flashes to mean the high-stage pressure switch circuit will not close during a high-stage-induced draft blower operation. Your furnace may have a pinched or blocked pressure switch hose, a blocked flue or loose wiring.

Read continuous flashing on the LED to mean your furnace has a reversed polarity of 115 volts. Turn off the power and correct the wiring polarity after reviewing the wiring diagram.

Feb 03, 2011 | Goodman Heating & Cooling

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