Modine PD-100 Burners won't fire.

[Parrinder]

Hello all,

I am new here and I have been looking through the threads hoping for an answer to my question but can't find one so I am posting this question.

I recently purchased a gently used 100K BTU Modine Garage Heater.

I got it home and installed (thanks for the tip about the drywall hanger, it was a life saver) connected the gas, electric and thermostat and fired it up. The pilot light lit right up and is constant and strong. The thermostat calls for heat and you hear the "click" from the ignitor, the fan fires up after about 30 seconds and blows great, but nothing from the burners. I took the thing apart and replaced the ignitor piece with a nice shiny new one, put it all back together, exactly the same outcome. I also read about the downdraft issue and checked and replaced the draft switch on the top of the unit. I am just wondering if there is anything else I can check or some simple trick I am missing for this. There seems to be NO gas moving from to the mixing tubes from the manifold, so the pilot light is not lighting anything. After I light the pilot I move the switch to "On". I feel like all of the "simple" things have been checked off. How likely is it that the gas valve itself is bad? I can replace it, but would think that would be a last resort. Thanks in advance.

 

[Done That]

Are you hooked up to natural gas? Can you verify inlet pressure at the valve?

Any chance the previous owner was running it on LP with an orifice change out?

Just thinking out loud around potential gas flow issues.....

 

[Greeny]

If it has a pilot light, I wouldn't expect an ignitor to be included.
I think the click you hear is the gas valve, but it isn't passing gas.

 

[Done That]

Yeah, it's spark ignition. I'm assuming he replaced the spark electrode....

Clicks may just be the tick tick tick of the DSI system.

 

[Parrinder]

Thanks for the responses.

The heater is natural gas, and was at the last owners.

There is a standing pilot light (no electric start) next to the ignition sensor (a little threaded rod that runs a copper line into the gas valve). The pilot light is pointed at this rod.

The valve unit is a RobertShaw 72C0ER setup for natural gas.

Again, I appreciate your input very much.

Thanks

 

[Greeny]

If it was working before, then you've probably got a minor problem that just needs a tweak to fix. There's NO gas coming into the burner when it clicks? Is there a thermocouple in the pilot flame? (Probably the threaded rod you mention) Is it solidly in the flame and thoroughly heated? I have checked these with a small torch heating them up in addition to the pilot. Maybe in the move the thermocouple got shifted out of the pilot flame.

Found this, look at Page 4:

https://yaleunion.org/wp-content/uploads/2014/12/75-551.pdf

 

[Done That]

The Modine control boards I am familiar with have two diagnostic LED's, 1 x green and 1 x yellow for flame sense. I would check the LED's versus manual or sticker in the unit and see if you hace any fault codes.

That is basically a proven/intermittent pilot ignition system. Gas valve pilot valve opens a bit for spark to pilot ignition, then when flame is sensed by the flame sense rod signal to the micro it allows the gas valve main valve to open.

Was the piece you replaced a combo spark electrode and flame sense rod? If so it should be clean. Pretty common to have to clean a flame sensor in a resi gas furnace over time otherwise.

 

[The Cobbler]

....
There is a standing pilot light (no electric start) next to the ignition sensor (a little threaded rod that runs a copper line into the gas valve). The pilot light is pointed at this rod.

it sounds like you're talking about the thermocouple. it's purpose is to sense the pilot & shut down the gas valve if there is no pilot . if the pilot stays lit, that's not the issue

do you have the gas valve in the run or heat position? or is it set to pilot?

 

[dw1]

it sounds like you're talking about the thermocouple. it's purpose is to sense the pilot & shut down the gas valve if there is no pilot . if the pilot stays lit, that's not the issue

do you have the gas valve in the run or heat position? or is it set to pilot?

Good info!! if the pilot is aimed and hitting the T-Couple it sends a mv signal to open the gas valve, if you have a meter, see if you have 24 volts at the gas valve (MV=main valve) if you do not have 24 volts there, you will have to adjust thermocouple.

 

[The Cobbler]

actually the 24 volts comes from a transformer. the thermocouple produces millivolts to open the valve for the pilot light only. if the pilot is staying lit , there's nothing wrong with the thermocouple .
the thermocouple is a safety for the pilot light only, if the pilot blows out, the thermocouple cools,stops producing millivolts and closes off the pilot gas .

 

[Milton Shaw]

I would still replace the thermocouple. Sounds to me like the spark lights the pilot and then the thermocouple confirms the pilot is lit and then opens the main valve. The gas for the pilot is controlled by the spark ign unit if it will light without you holding down anything. Thermocouples are not much money so I would try one before I went looking farther. Also there is some time (maybe two minutes) involved there before the main valve should open.

 

[The Cobbler]

....

There is a standing pilot light (no electric start)
Thanks

Sounds to me like the spark lights the pilot and then the thermocouple confirms the pilot is lit and then opens the main valve. The gas for the pilot is controlled by the spark ign unit if it will light without you holding down anything. Thermocouples are not much money so I would try one before I went looking farther. Also there is some time (maybe two minutes) involved there before the main valve should open.

he has already stated it's a standing pilot. I maintain the thermocouple is there to allow the gas valve to open for operation. if the pilot goes out, the thermo stops making mv and therefor does not allow the gas valve to open.
that will also shut off the gas supply to the pilot. if the thermo is faulty, the pilot won't stay lit.

 

[Scott65]

Switch the polarity of the electrical plug. Wherever the wires come in to the unit, pull it apart and switch them around. With the number of other things that you have tried I am guessing it may be that simple.

 

[Parrinder]

Hi All,

Thanks for the responses. Still no luck on this. The heater does have a standing pilot light, meaning there is no electric switch for it. You turn the valve to "pilot" and manually light it. I replaced the thermocouple with a new one, and it is directly in the middle of the pilot light and glows nice and red. I tried reversing the switches (good idea) but still no luck. As for the electric board, there are no lights/led on this thing. It just a transformer in the middle of a switch board. At this point I am thinking it is the valve for some reason and am going to try and swap that out. Almost ready to put in a service call (shudder) and have someone come take a look at it. Just need it fixed before the snow flies in Minnesota.

Also, thanks to Greeny for the great link. It didn't fix my problem but had some good info!

Thanks again for everyone's input. I will update this when I have it running.

 

[danpik]

There are two basic types of standing pilot burners in use. The first is a therm-COUPLE. This utilizes a probe that is in the pilot flame and has a small dia copper tube connected to it. The probe is ~1/8"-3/16" dia. The pilot flame heats the probe and due to dissimilar metals it generates a small voltage at the tip. This voltage is sent down a small wire that is inside the tube and triggers the gas valve to allow the pilot lite to stay lit. It will have nothing to do with the operation of the gas valve other than proving the pilot lite. The operation of the gas valve is via a 24 volt signal from a transformer thru the thermostat and any proving switches in the circuit.


The other method is a thermo-PILE. sometimes referred to as a power-pile or power generator. This type of system uses a probe in the pilot lite that is about 3/8" dia. It will have two wires coming from it going to the gas valve. The terminals on the gas valve where these connect are the TH/TP and the TP . The voltage generated by the thermo-pyle is the voltage that the gas valve uses to operate. This is, under ideal conditions, 750 Mv. If the voltage is too low <500 Mv the unit will not operate properly. The voltage from this also goes thru any and all proving switches as well as the thermostat. If any of the proving switches is not closing the unit will not fire.

The OP's unit sounds like it is a thermocouple unit. It sounds to me like there is either a gas flow issue. Or a transformer issue not supplying enough voltage to operate the gas valve. If both of these can be verified, then I would suspect the gas valve itself is bad
Dan

 

[Pointbock]

My $ is on the valve. My PA30 valve died last year. Maybe they're serviceable but for what it cost, I just replaced the whole thing. No more problems.

 

[brewchief]

Do you have 24v at the gas valve? Did those wires get moved at all?