Question about Mr. Heater MH170FAVT Open Flame Gas Utility

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Heater won't relight after shutting down, but fan continues to run

Heater lights properly, but flame shuts off after about 5 minutes, no matter what thermostat setting. The fan continues to run, but the flame won't relight automatically when temperature drops below thermostat setting. Heater won't stay lit when thermostat is set at max temp. setting. Running off of 1000 gal LP tank with commercial regulator installed by gas supplier.

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  • Roger Hornaday Dec 25, 2013

    This heater is being used in a 30FT x 30FT x 12FT high building and worked fine for years.

  • Roger Hornaday Dec 25, 2013

    To answer your questions. John, the flame is the normal blue with occasional yellow tips. There is the normal roaring sound when the unit is ignited and the flame is normal size. When it does shut off the flame, it is as if the thermostat abruptly shuts it off, but it doesn't seem to matter where the thermostat or flame control are set as to the length of time that the unit stays lit and when the flame shuts down the blower fan keeps running. Voltage is normal and there is plnty of propane in the tank (it was just filled in October and is a 1,000 gal tank). The original pressure regulator was replaced by the LP gas supplier several years ago with a larger commercial regulator and was set by them to the proper specs. and there is no frost on the pressure regulator or gas smell indicating a malfunction there and the unit worked well until recently. I will check the high limit switches and terminal block, as well as the thermostat continuity at different settings, as well as all connections. Any additional help would be greatly appreciated. Thank you!

  • Roger Hornaday Dec 25, 2013

    John, I checked the continuity on the high limit switches and thermostat, checked all wire connections, cleaned the igniter plug, checked the resistance on the gas valve solenoid and again checked the pressure regulator. All checked out good. Is it possible that the solenoid for the gas valve is sticking shut and causing the problem? I tried manually shutting off the flame by turning the thermostat off and waited 7 minutes and still could not get the unit to light. I heard the igniter and the solenoid for the gas valve energize, but it wouldn't light. The limit switches were room temperature and closed. Any help would be greatly appreciated.

  • Roger Hornaday Dec 26, 2013

    John, The gas valve is the original Goyen Model# 10QG-EDANA-7281 valve. The resistance on the coil is 217.9 ohms. Jumping out the thermostat didn't solve the problem. It still shuts the flame off in 6 minutes and both high limit switches remain closed. I do have an engineering degree and did disconnect and isolate each component when doing continuity tests. I do not, however, have a manometer and since the secondary regulator (3/4" commercial grade) supplying this heater was professionally installed, using 3/8" copper tubing for supply and outlet to the 1/2" black pipe nipple and shutoff valve inside the building, by the LP gas supplier and they own the 1,000 gal. tank, I will have to call them to have that checked. The shutoff valve is fully on at the tank and inside the building that the heater is in. This tank also supplies the 95,000 BTU furnace inside my house with no problem with the regulators freezing up. I did find out that the gas valve on the unit is shutting the gas off for some reason after 6 minutes and the unit can't be restarted for about 10 minutes affter this happens (The gas valve will not open even with the thermostat jumpered out). Is it possible that the problem could be caused by the control board? The igniter spark is a strong blue spark, even when the gas valve won't open.

  • Roger Hornaday Dec 27, 2013

    John, I checked the voltage to the gas valve solenoid with an autoranging true RMS meter and it is staying between 117 and 118.6 volts while the flame is burning and the voltage is still there when the flame shuts off, but decreases to about 45 volts and less, a couple of minutes after the flame shuts off. To eliminate the gas lines and regulator, the company that supplies the LP gas and the hookup replaced the regulator with a new one and checked the gas pressure, which is to spec. The unit is still shutting off after 6 minutes. The igniter plug on this unit also acts as a flame sensor and is glowing orange when the flame is lit. There is no oxygen depletion sensor on this unit, but the blower has plenty of suction into the unit and there is no impeded air flow. Could it be that the flame sensor portion of the ignitor is going bad or is that contained in the flame control board? I cleaned the ignitor plug and it didn't seem to help. The unit consistantly shuts off the flame after 6 minutes, no matter what setting the thermostat or the BTU output control valve is set at. If it were something in the gas valve causing this it would seem that it would be more inconsitant, which leads me back to either the igniter plug or the flame control board.


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Roger, you either have a gas supply issue or a voltage problem.
Since I don't know your aptitude and abilities pertaining to LP gas troubleshooting/testing procedures, I don't know how detailed you want to go...basically, make sure your propane tank isn't empty; or that the pressure regulator didn't freeze up. Make sure that it is rated and set for 28" of water column output.
Check to make sure all the wire connections are secure to the flame control terminal block and to each of the hi-limit switches.
Isolate & perform continuity checks to each electrical component, including the gas valve.
You'll need a manometer to test and set the gas input & output water column levels.

When the unit is running,, what color is the flame?
Is there a roaring sound?
Is the flame small and weak?

Posted on Dec 25, 2013

  • 3 more comments 
  •  John
    John Dec 26, 2013

    Hi Roger- I just want to double check that you performed the continuity tests correctly because I had another person who I instructed and did not understand what I meant when I told them to isolate the cycling thermostat, hi-limit thermostat, & thermal fuse to their gas dryerbefore performing taking resistance readings. So please don't feel slighted that I'm asking. You did remove any leads (wires) to each of the components you tested, correct? Just because you see no icing or frosting around a gas regulator does not mean that it is okay. There is moisture in the lines that carry propane & natural gas; hence drip legs- so the regulator could in theory be frozen internally. That's why I suggested taking pressure readingsusing a manometer to ensure there is proper gas flow and at 28 inches of w.c.. Speaking of gas flow, I would also check the inlet and outlet pressure (using a manometer) at the ags valve too. Process of elimination to determine why gas valve is not opening to release the gas.. It could be like the regulator, internal freeze do to condensation build up in valve. It could be a bad gas valve assembly; a bad gas valve coil; or a clogged orifice. Is the spark on the spark plug weak or strong? Did you try jumping out the thermostat?

  •  John
    John Dec 26, 2013

    What is the make and model number to the gas valve?, please.

  •  John
    John Dec 26, 2013

    BTW, is the shutoff valve on the LP tank fully open? And is the pressure regulator and gas valve rated for LP gas?

  •  John
    John Dec 27, 2013

    Roger, I contacted Goyen, the manufacturer of the low pressure gas control valve (a subdidiary of Pentair Environmental Systems). They're supposed to send me the data sheet specs on it. In the meantime, what voltage reading are you getting at the valve during normal operation- and does the voltage drop out after you lose the flame? What about the oxygen depletion sensor, is that kicking in causing the flame out? I have been on service calls where such things as a dead spider in the vent limiter or breather cap as being the culprit as the cause of low or no gas flow from the regulator to the appliance. I have also gone on calls where "professional" installers improperly connected gas regulators- reverse flow; improper orientation; sizing; and using NG regulators on LP installs; so I leave no stone unturned when troubleshooting problems like yours, especiall when this is being done remotely and I'm not there.

  •  John
    John Dec 27, 2013

    And yes, it is possible that the control board is the problem. You'll have to troubleshoot it at the component level.


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I had to replace the regulator. If you have a propane appliance shop near you, you can probably just get the nipple that goes into the bottle. It's aboit 3/16" diameter, 3/4" long and may have a 6 sided end up inside the screw on cap of the regulator.

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SOURCE: Stays lit for 25 minutes and shuts off

How large and sealed of an area are you using it in? I ask because those units have a low oxygen sensor which will shut it down if there is not enough oxygen in the space.(kinda prevents that pesky suffocation thing). Otherwise if using it in larger cold spaces, the issue is can be from the smaller tanks. As mentioned above, a larger tank can solve this, because these units have a fairly good input rate, which will cause the smaller tanks to freeze, and lower the propane temperature and evaporation rate, basically runs out of gas until the tank warms back up.

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SOURCE: heater shuts off

The heater thermostat senor for this heater could be bad or indicating a abnormal temperture shutting it down. You might want to return item if still under warranted

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SOURCE: heater turns on and heats

Problem: Your furnace will not ignite the gas to produce heat for your home. When a furnace has a bad ignitor what I see most of the time is the following sequence of operation:

1. Thermostat calls for heat. 2. Draft inducer motor starts. 3. Pressure switch attached by a small plastic or rubber tube senses the negative pressure produced by the draft inducer and closes. 4. Draft inducer runs for 30 seconds to a minute before you hear a gas hissing sound. The ignitor did not glow, the flame sensor (a small metal probe about 1/8" in diameter, with a white porcelain base) does not sense the flame, so after 8 to 10 seconds the hissing sounds stops with no ignition of gas to heat your home. Your furnace shuts down and goes into a lock out condition until you turn your power switch back off and on again. Then the sequence starts all over again with no ignition of the gas. Solution:You probably need to purchase and install a new ignitor. I would suggest that you inspect your ignitor closely for cracks. Make sure you do not touch the ignitor with your bare hands. If you do not visually see a crack, then you could have a furnace control board problem or a limit, rollout switch problem. The furnace's control board might not be supplying the voltage to the ignitor.If your furnace lights and the gas stays on for 8 to 10 seconds, then shuts right back off, then you need to clean your flame sensor with light sand paper or steel wool. You might need a new flame sensor, but most of the time they can be cleaned an will work well after cleaning.

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