Hot Dawg 75K Fault Code

So, I went to turn my heater on this morning, just to make sure everything was good..........nope

It turns on, fan blows, and no warm air

I take off access panel and the LED has 3 flashes

Any quick and easy ideas, that I can check myself?

Roll out switch is bad, unless you have a hole in your tube letting flames out. Go to youtube and type in roll out switch. Easy to replace 2 Phillips screws and 2 push on wire connectors.

I have two rollout switches.......why would both be bad?

Aren't the rollout switches controlled by the limit switch?

Is there a wait to test the rollout switches or the limit switch?

Yes. They are open/closed. Normally is has to be in the closed state. Can "test" by jumping the 2 wires together.

Roll out switch shuts down unit when is gets HOT, like open flame and over time. Opens the contacts. Some you can reset with push button, some are just one time use

So unplug both switches and insert a jumper wire into the two wiring harnesses, both for the upper and lower switch?

What about the limit switch, same way to test?

Installed jumper wire at the tstat.........same problem

Installed jumper wire at the tstat connection inside the heater.....same problem

I then reversed the black/black and white/white wires.......same problem

I then removed the limit switch and let it hang on the side of the heater......same problem

Each time I had to manually reset (by pushing the red pins) on the upper and lower rollout switches

Any other suggestions to try?

Maybe not much help, but from your other thread, didn't you just purchase the heater? If so, I would contact Modine and go from there.

Any chance this heater was factory setup for propane and now it’s connected to NG ?

Might want to double check ?

When i bought it, it had NG labels on the valve cap

The burners turn on and fire up, but around the 3-4 minute time, it shuts down and throws the code

Yes, understand.........but it appears to be over firing or under venting........the wrong gas pressure or gas type setup might cause those symptoms. Just thinking out loud from a distance.

Maybe the gas valve needs to be adjusted?

Can I add a jumper wire to the flame rollout switch to see if it still shuts down?

Can I add a jumper wire to the limit switch to see if it still shuts down?

Safe to do, to rule parts out?

To rule out the tstat, I installed a jumper wire for the tstat in the panel........same thing, shut down in about 3-4 minutes

I then rewired the tstat wires like it should be and moved on

While it was flashing 3 codes...........I manually pressed the bottom flame rollout sensor with a long screw driver. No change, still flashing

I then manually pressed the top flame rollout sensor and it fired back up, but in 3 minutes the heater shut down and the 3 flash code was back

I then removed the two wires from the top flame rollout sensor and installed a jumper wire.........the heater ran for 15 minutes without any issue

SO, would this obviously mean that the top flame rollout sensor is bad? For $20-$25 should I order a new sensor and only replace the top one?

Would it be a good to mark the top one with a black marker......and flip the top and bottom flame rollout sensors and see what happens?

Any ideas or suggestions?



Jumper wire

I read a lot and researched a lot today........

Some say just unplug the top flame rollout sensor and don't worry about it.......meh

Some say to adjust the gas flow down alittle, on the valve......maybe

Then I found this GJ posting:

https://www.garagejournal.com/forum/showthread.php?t=27597&highlight=flame+rollout&page=2

"Here is the fix..... Basically you take out the top burner and pinch shut the top fan (I used a vise). The bottom fan on the top bruner is still required for lighting. I'll try and post the pic when I get a moment.

From Mr. Heater:
The Big Maxx unit heaters have one or two roll out sensors and one high limit sensor heat exchanger to monitor over heating or flame blowing back into the burner box.

A common problem on these units is the LED on the circuit board giving a 4-flash code ‘High limit or rollout switch open’. The problem that causes this is that the burners that the flame comes out of, are designed to overlap their gas so as the bottom burner lights up the gas and flame hit the gas from the burner right above it. So each burner lights up one after the other. The top burner doesn’t have a burner above it to light up but the gas and flame still comes out. This little extra flame hits the heat exchanger tube before being sucked down into the tube. This flame than causes the upper mounted rollout heat sensor to go off and the heater shuts down. You can reset this rollout heat sensor with the little reset button that is located between the wires that plug into the back of it. It is located at the top of the burner assembly behind but not on the circuit board.

To fix this problem, you will need to remove the top burner and pinch together its edges per the pictures below. Remove the burner side plate, than remove the two screws that hold the burner in place and pinch or hammer the top edge, just above the center hole to stop this extra gas path

View attachment MHU75 Burner adjustment complete.pdf

I am going to try this burner pinch solution today, even though it is for a Big Maxx heater.....

Hope this fixes it for you.

I'll be subscribing to this thread for sure. My luck, mine will do this when I install it, too.

IT IS FIXED...............Read along

Using that link and the PDF file for the Big Maxx, I fixed it in about an hours time

The burners are all same, but the top one does not need to open pinch, so the flames can "leak" upwards and help to ignite another burner

The top burner does need to be pinched closed and I used my vise. I was going to JB Weld it, but was concerned it would not hold up to the heat, so I welded the top portion closed

I used my temp gun and now the top and bottom flame rollout switches both read within 10 degrees of each other and the top switch is 80 degree COOLER

The end of the burner was pinched and welded shut, and another small gap on the top was also pinched closed and welded










Here is the bottom burner......again, they are all the same. See the small flame rollout on the bottom, this rollout was larger on the top most burner and I think the fan was hitting this area, blowing the flame back towards the switch



See the nasty booger welds sealing it all shut, HAHAHA



The world is a better place


I put the front and side cover back on and reinstalled the air louvers

The heater fired up and ran without issue for over 30 minutes

Okay. I have 3 blinking lights. Changed switch same lights. I changed batteries in the a thermostat in the house. When I put the thermostat back it read 60 degrees. Checked lights blinking once. Meaning working normal no demand for heat. Turned up thermostat and 3 blinking lights again. I can hear click but that’s it. No clearing fan or anything.

Thanks for ideas

I did the tube with a paper clip. Mr heater 50 k

fishspike57 said:

Okay. I have 3 blinking lights. Changed switch same lights. I changed batteries in the a thermostat in the house. When I put the thermostat back it read 60 degrees. Checked lights blinking once. Meaning working normal no demand for heat. Turned up thermostat and 3 blinking lights again. I can hear click but that’s it. No clearing fan or anything.

Thanks for ideas

I did the tube with a paper clip. Mr heater 50 k

Click to expand...

3 Flashes
Pressure switch failed closed before CAB is energized or failed open after CAB is energized

That “clearing fan” or exhaust fan not running is likely he problem.