20 Most Recent Mr. Heater MHU75NG Questions & Answers

3 flashes could be the pressure switch ,jump it out see if it lights or clean the flame sensor or check the snap dice's 1 for high temp and 1 for low temp ..

Make sure you are getting 24 volts back from thermostat and you are getting good connections. If you have 2 wires running to stat, connect them together at unit and see if unit starts. Check for wires unplugged, but I think that a flashing green light means you have 120 volts supply and the stat is not calling for heat

did you put a drip pocket on the line to the heater

There is something else that is causing the Overload/Roll Over Switch to trip. You can try unplugging the unit from it's electrical source and wait 30 minutes before plugging it back in. That may allow it to reset itself. Unfortunately the Overload/Roll Over Switch is preset at the factory and is not adjustable.

If the unit resets itself and starts working again, but then shuts down, check your Owners Manual for other causes. If you've misplaced your Owners Manual, here's a link to it, that you can download and print.

http://www.heaterstore.com/images_templ/mr-heater-heaters-mhu45-75lp-ng.pdf

Hope this helps to get you headed in the right direction. If all else fails, call the Technical Service Dept at the number listed in the Owners Manual.

There is a flame sensor located in the last burner that lights up. It is either not seeing flame or not getting flame to it within a certain time. Check the wire that comes from it and goes to the circuit board for a bad connection. Check any ground wire connections for a bad connection. Pull out flame rod (sensor) and polish it with a scrub pad or soft wire brush. If none of these recommendations help, replace the flame sensor. Make sure the flame travels to the last burner, if not, clean the flame tray that allows the flame to go from one burner to another.

the high limit is an over heat switch that could mean the unit is over fired. you would need to time input or check manifold pressure. the roll out switch is a switch that shuts the unit off if combustion is spilling at the divitor on the unit where the vent connects. with this you need to check your venting

I had this same problem with my heater. I cleaned the propane tube where the flame comes out (after it’s off and cooled down) with a Qtip and some alcohol. After removing some cotton, it will fit all the way down to the end of the tube. Repeat until it comes out clean and stays lit. I had to repeat with 91% rubbing alcohol and more Qtips, and most of the cotton removed.

Check out the pressure switch . and the snap disk .

check the pressure switch and the snap disks

Tis atomizing the fuel so it'll burn hotter/better. up their loud tis normal.

You will probably need to remove the pilot orifice and clean it out use a small needle or orifice cleaning rod. The pilot flame is not big enough to keep the thermocouple engaged.

Yes no flame to thermocouple it will shut off

With multimeter check l1 to ground on control board. Also check 24vac to ground to verify high and low voltage present at board.

chw=eck flame sinser need clean