Stumped! Another Big Maxx Problem

[Plump]

I've read and applied all the fixes I've seen here and YouTube and I'm just STUMPED! So, Big Maxx 50,000 BTU that fires up but doesn't blow enough gas/heat. The fan just blows cold air.

I replaced the gas valve since I thought that HAD to be it. It was converted to LP and I'm getting 12WC in but very little past the gas valve. Tested the power going in and it was just a tick about 24 volts. Customer service said it might be the panel but it's testing fine. It was sitting around in a box for a year since I was getting a new roof and wanted to wait to put a hole in the garage roof so it's brand new (but of course out of warranty now!)

HELP!!!! I'm completely at a loss here.

 

[Plump]

 

[PoorUB]

It was converted to LP and I'm getting 12WC

12" WV after the gas valve? Does it have the correct orifices in the burner?

 

[Plump]

12" WV after the gas valve? Does it have the correct orifices in the burner?

Before the valve ("in"). Yes, the spring and orifices were changed in the conversion.

 

[Noltz]

That's 12" WC with the unit running, right?

I see you chimed in on another old thread about a similar setup. Are you running dual tanks like you wanted to? Did you ever have this machine running on NG? I feel like the flames are undersized. I didn't watch this guys whole video (I'm at work) but this clip here at 6:20 looks like a larger flame front than your photos?

 

[PoorUB]

Before the valve ("in"). Yes, the spring and orifices were changed in the conversion.

What is more important is the gas pressure after the gas valve, right before the burner.

That's 12" WC with the unit running, right?

I see you chimed in on another old thread about a similar setup. Are you running dual tanks like you wanted to? Did you ever have this machine running on NG? I feel like the flames are undersized. I didn't watch this guys whole video (I'm at work) but this clip here at 6:20 looks like a larger flame front than your photos?

Good point! Gas pressure with the unit off means very little. Check pressures with the unit running. It will verify you gas supply is adequate. You might have too small of line size to the unit, or can not vaporize enough gas in the tanks to supply the unit.

My bet is the gas pressure while the unit is running is too low for some reason. Check and get back with us.

I see guys running a two stage regulator on the tank and 50 feet of 3/8" copper and the copper kills the gas flow.

 

[fitter30]

Size of tank in gallons? Size and length of lp piping and where the regulator are piped.

 

[Plump]

Two 100 lb. tanks. I did run it on one, trying to identify the problem but it made no difference. Brand new regulator after trying three other ones. 1/2" Black pipe into 1/2" CSST. 15' total? Not a long run at all.

 

[arrowhead]

What's the delta temperature across the unit? Maybe it's blowing cold air because the air going in is really cold. What's the outdoor temp? Propane tanks are sized based on surface area not so much as storage capacity. Think of propane as freon, it actually boils off in the tank to make the vapor - and cools the tank down like a refrigerant. If you don't have enough surface area to evaporate the enough vapor to keep up with the load, your pressure will drop. Which is a double whammy as the outside air temp drops the demand increases which in turn cools your tank off even more and lessens it's recovery rate. None of this might relate to your problem but just something to keep in mind.

 

[PoorUB]

Two 100 lb. tanks. I did run it on one, trying to identify the problem but it made no difference. Brand new regulator after trying three other ones. 1/2" Black pipe into 1/2" CSST. 15' total? Not a long run at all.

Have you checked the gas pressure, at the burner manifold with the unit running??

 

[The Cobbler]

the spring and orifices were changed in the conversion.

is there a chance the orifices could be wrong? and as mentioned, check the gas pressure after the valve. some gas valves have adjustments for burner & pilot. also what is the BTU rating for your regulator ?

 

[Noltz]

Might be worth your time to do like this and get a gauge on the supply line. You should be just fine with ½". This old 100k BTU heater pulls 8"WC static down to 5.5" running on the end of 12' of ½" pipe.

 

[Plumber338]

What's the delta temperature across the unit? Maybe it's blowing cold air because the air going in is really cold.

What arrowhead said. These heaters are designed for a 45 degree temperature rise across them. If incoming air temperature is 20 outgoing will be 65. Also at 80% efficiency you only get 40K of heat from a 50K input. Those flames look pretty close to what I have in my Modine unit.

 

[toyotadriver]

What arrowhead said. These heaters are designed for a 45 degree temperature rise across them. If incoming air temperature is 20 outgoing will be 65. Also at 80% efficiency you only get 40K of heat from a 50K input. Those flames look pretty close to what I have in my Modine unit.

Another vote for this. OP lives in a cold area.


Few more questions:

What size area are you trying to heat?

What outside temp? Flames look ok to me but a 100lb tank, if it's extremely cold, might not vaporize enough propane. The dual propane tanks would help if the OP is drawing from both at the same time. I've run an 80k furnace off a single 100lb propane tank without issue but my outside temps never got below about 0* and most of the time were substantially warmer than that.





Nothing in this post should be misunderstood, interpreted, misinterpreted, or construed to be of a political nature.

 

[Plump]

It was 45 degrees in the garage and I'm getting no heat. It's not trying to warm up super-cold air, that's for sure. Again, getting 12" WC on the inlet to the gas valve so pressure to the unit is not (seemingly) a problem. Just too low of pressure after the valve. Going to try replacing the board to see if that does it. Makes no sense but I've tried everything else! Grrr!

Thanks!

 

[PCustoms]

It was 45 degrees in the garage and I'm getting no heat. It's not trying to warm up super-cold air, that's for sure. Again, getting 12" WC on the inlet to the gas valve so pressure to the unit is not (seemingly) a problem. Just too low of pressure after the valve. Going to try replacing the board to see if that does it. Makes no sense but I've tried everything else! Grrr!

Thanks!

How long did you run it?

If it fires up and runs consistently I'd let it cycle. Not sure changing the board is magically going to change the BTU output or fix if your tank is too small.

 

[Plump]

It doesn't heat despite running for quite a long time. Two 100-lb tanks hooked up together and again, getting plenty of gas to the inlet. Maybe the board just isn't calling for enough gas, is the only thing I can think of?!? It takes two-three cycles to get it to fire all three burners and then they run at a bare minimum, not blasting enough heat to get the diffuser to heat up enough for the fan to blow heat.

 

[PCustoms]

It doesn't heat despite running for quite a long time. Two 100-lb tanks hooked up together and again, getting plenty of gas to the inlet. Maybe the board just isn't calling for enough gas, is the only thing I can think of?!? It takes two-three cycles to get it to fire all three burners and then they run at a bare minimum, not blasting enough heat to get the diffuser to heat up enough for the fan to blow heat.

Pretty sure the board doesn't control the gas, other then on/off.

Your tanks are likely too small, as pointed out before.

 

[arrowhead]

It doesn't heat despite running for quite a long time. Two 100-lb tanks hooked up together and again, getting plenty of gas to the inlet. Maybe the board just isn't calling for enough gas, is the only thing I can think of?!? It takes two-three cycles to get it to fire all three burners and then they run at a bare minimum, not blasting enough heat to get the diffuser to heat up enough for the fan to blow heat.

You said the gas valve was converted, did you change out all the burner orifices too? They have a larger hole as it takes more propane flow for the same amount of btu

 

[fitter30]

Check the pressure outlet of the gas valve has a tap need a allen wrench, 1/8" mpt x 5/16 hose adp. & manometer u can make.

 

[toyotadriver]

You said the gas valve was converted, did you change out all the burner orifices too? They have a larger hole as it takes more propane flow for the same amount of btu

You've got that backward. Natural gas has larger orifices than propane. Natural gas is lower pressure than propane.

This is going to take some diagnosing.

OP does the fan that blows the heat into the room come on at all?

What is the manifold pressure? Not the pressure to the heater. The pressure that is headed to the manifold. It's adjustable per the manual. See figure 9 on page 10 of the manual. Then read page 15-16 of the manual.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwi2hI7mxZqDAxV6j2oFHcvuDLUQFnoECBkQAQ&url=https%3A%2F%2Fwww.mrheater.com%2Fmwdownloads%2Fdownload%2Flink%2Fid%2F30&usg=AOvVaw0yHx8bpYUpAcznZ35woihT&opi=89978449

Here's something you can try.....turn the heater on and turn all the lights off. You need it to be dark inside the shop/garage. Cover up windows if you need to. The burner tubes come out of the burner and make the first turn in the heater exchanger. Let the heater run for a few minutes. While in the dark, look at that first burner bend. It should be glowing faintly red on the outer radius of the tube. Report back what you see.


Nothing in this post should be misunderstood, interpreted, misinterpreted, or construed to be of a political nature.

 

[arrowhead]

You've got that backward. Natural gas has larger orifices than propane. Natural gas is lower pressure than propane.

This is going to take some diagnosing.

OP does the fan that blows the heat into the room come on at all?

What is the manifold pressure? Not the pressure to the heater. The pressure that is headed to the manifold. It's adjustable per the manual. See figure 9 on page 10 of the manual. Then read page 15-16 of the manual.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwi2hI7mxZqDAxV6j2oFHcvuDLUQFnoECBkQAQ&url=https%3A%2F%2Fwww.mrheater.com%2Fmwdownloads%2Fdownload%2Flink%2Fid%2F30&usg=AOvVaw0yHx8bpYUpAcznZ35woihT&opi=89978449

Here's something you can try.....turn the heater on and turn all the lights off. You need it to be dark inside the shop/garage. Cover up windows if you need to. The burner tubes come out of the burner and make the first turn in the heater exchanger. Let the heater run for a few minutes. While in the dark, look at that first burner bend. It should be glowing faintly red on the outer radius of the tube. Report back what you see.


Nothing in this post should be misunderstood, interpreted, misinterpreted, or construed to be of a political nature.

OK I stand corrected, but did the correct orifices get installed? (I fixed my last post)

 

[toyotadriver]

OK I stand corrected, but did the correct orifices get installed? (I fixed my last post)

No worries!

I kind of suspect the issue the OP is having is the wrong setting on the gas valve itself. But, he's not being very responsive with diagnostics so he's making it hard for us to help him.

Part of diagnosing things is to test various possibilities. Once you eliminate the things it ISN'T, then you can find the thing that IS causing the problem. Several posters in this thread are trying to get the OP to check certain things but he won't. So, it's impossible to help him fix the issue if he won't test out the various tests he's been recommended to perform.

Helping someone diagnose a problem on a message board can be very frustrating if the person doesn't perform the various tests and then report the results. I like helping figure out problems but numerous times in the past on various forums, I've tried to help people figure out their problems and they don't do the tests and report the results. Eventually, I just give up.







Nothing in this post should be misunderstood, interpreted, misinterpreted, or construed to be of a political nature.

 

[Plump]

No worries!

I kind of suspect the issue the OP is having is the wrong setting on the gas valve itself. But, he's not being very responsive with diagnostics so he's making it hard for us to help him.

Part of diagnosing things is to test various possibilities. Once you eliminate the things it ISN'T, then you can find the thing that IS causing the problem. Several posters in this thread are trying to get the OP to check certain things but he won't. So, it's impossible to help him fix the issue if he won't test out the various tests he's been recommended to perform.

Helping someone diagnose a problem on a message board can be very frustrating if the person doesn't perform the various tests and then report the results. I like helping figure out problems but numerous times in the past on various forums, I've tried to help people figure out their problems and they don't do the tests and report the results. Eventually, I just give up.







Nothing in this post should be misunderstood, interpreted, misinterpreted, or construed to be of a political nature.

Not sure what I haven't answered. Used a manometer to test both gas going TO valve (12.2 WC) and AFTER the valve (near 0 WC). The fan blows plenty hard. The little bit of blue flame isn't heating up the coils hardly at all. Laser thermometer is showing 68 degrees after running for a long time; not nearly hot enough to cause the blowing air to be heated.

The orifices are the correct ones for LP

I've messed with the gas valve pressure setting both by tightening and loosening; that does nothing, seemingly. The manifold is still not blowing enough gas to make a difference. Again, this is a brand new unit and a brand new gas valve that I just installed.

I mentioned the board changeover possibility since I was thinking maybe it isn't calling for enough gas through the gas valve to make a working heater. Power seems to be OK but maybe it's just not asking for enough LP.

 

[Plump]

And HOLY COW. I responded YESTERDAY! Tough crowd.

 

[PCustoms]

I'd change your gas valve before the board.

 

[Plumber338]

Not sure what I haven't answered. Used a manometer to test both gas going TO valve (12.2 WC) and AFTER the valve (near 0 WC).

Your manifold pressure (after the valve) is 0" WC??? It should be 10" if you are between sea level-2000 foot elevation, 8.5 if between 2000-4500.

as toyotadriver said:

What is the manifold pressure? Not the pressure to the heater. The pressure that is headed to the manifold. It's adjustable per the manual. See figure 9 on page 10 of the manual. Then read page 15-16 of the manual.

 

[toyotadriver]

Not sure what I haven't answered. Used a manometer to test both gas going TO valve (12.2 WC) and AFTER the valve (near 0 WC). The fan blows plenty hard. The little bit of blue flame isn't heating up the coils hardly at all. Laser thermometer is showing 68 degrees after running for a long time; not nearly hot enough to cause the blowing air to be heated.

The orifices are the correct ones for LP

I've messed with the gas valve pressure setting both by tightening and loosening; that does nothing, seemingly. The manifold is still not blowing enough gas to make a difference. Again, this is a brand new unit and a brand new gas valve that I just installed.

I mentioned the board changeover possibility since I was thinking maybe it isn't calling for enough gas through the gas valve to make a working heater. Power seems to be OK but maybe it's just not asking for enough LP.

Now that's some useful info. So, you have plenty of gas going to the valve so that side is good. It appears there's an issue with the valve. We now know the problem now we just need to find the cause of the problem. Could be several causes. Since it was converted to propane from natural gas, was the gas valve also converted? See pg 14 of the manual. Have you tried adjusting the pressure?

Here's the Honeywell gas valve manual.

https://honeyvell.energy/wa-data/public/site/gazovye-klapany-Honeywell/Manual Honeywell VR8205 (en).pdf

Looks like you need this kit part number to convert from natural gas to propane. 393691






Nothing in this post should be misunderstood, interpreted, misinterpreted, or construed to be of a political nature.

 

[JBushman]

Did you check the inlet pressure when the unit was running? It should remain constant. If it doesn’t you may have a partial blockage.

Mine was working fine one day and it got real cold and wouldn’t light. I took a heat gun to the regulator at the 100lb tank and melted the ice and snow off. Worked fine. Ship got toasty. Didn’t use it the next day. Day three went out and it fired but was barely blowing warm air.
Connected manometwr to inlet side and it read 12. Checked manifold side and it read 2.
Went back to inlet side read 12 until I turned it in and once it lit it dropped and held at 2.
Something is not allowing enough gas to get to the valve. Will tear apart this weekend and check filter screen and black pipe for instructions.