Modine Heater Problem

[Donald shaffer]

We have a 2100 square foot garage. We have Modine propane heaters in it. The upstairs is 900 sq. ft. with a 75000 model #PAE75AC. The chimney is 8" double wall, 7ft. above the peak of the roof. The one downstairs works just fine. The one upstairs will not stay running. Pilot light stays on but will pop the blocked vent safety switch. Replaced the switch and started it back up, will run for awhile then do the same thing. If I open the door or window a little bit it will run and run and run for weeks with no problem. OK, so I put a 4x10" hole in the floor still no good. Put 4" hole in wall still no good. Put 4" fan in wall still no good. Don't know what else to do. PLEASE someone help.

 

[D45]

Replaced the limit switch or the flame rollout switch?

Check your top burner for flame rollout towards the switch........does the heater have any "flash codes"?

Check out my recent issue with my 75K Hot Dawg (Modine):

https://www.garagejournal.com/forum/showthread.php?t=374715

 

[Donald shaffer]

Wasting Dollars & Wrenching In Indiana ,thank you this older Modine PAC has a limit control switch , but i have to reset the blocked vent switch all the time . Does the limit switch make the BVS switch pop

 

[TurnipTruck]

I had a very similar problem with a 35k btu modine.
During a remodel, I removed the upper 15 feet of flue while re-siding, and every day I would have to reset the rollout switch. We never had the problem in all the years before, when the flue was much taller and the draft was therefore much greater.
What diameter is your flue, and can you add another section or two?

 

[Donald shaffer]

I have 7 ft above the peak now dont think i can add more ,all but need a light on top now.Did add 10 to get it that far up . The pipe is 8 in. thank you ,im at a lost for new things to do

 

[BillK]

Donald,
Is this a new installation or has it run fine in the past and suddenly there is a problem ? If it was fine in the past, what has changed ? Any chance that the flue actually is blocked ? Where are you located ?

 

[Donald shaffer]

BillK I have had problem with it from day 1 . The hole system is new ,as before it will run if i open a window or door a 1/2 " . The flue is open ,the one down in garage is fine .We live in MD. in the mountains,trees on 1 side, open on other sides .

 

[BillK]

Donald,
If you run the upper one by itself will it work ok ? Maybe the combination of both of them needs too much air ? When the upper one is running does it have a nice blue flame ? Or bunch of yellow ?

 

[Donald shaffer]

BillK I can run the one down stairs with no problem. I can have the one upstairs run by itself and with the one downstairs as long as I have the door or window open a 1/2". The upstairs and downstairs have nice blue flames.
The one upstairs will run without the one downstairs but still has to have the 1/2" opening of the door or window.

 

[Caddybill]

Not enough make up air. Both units running together are using all the free air in the space.

 

[BillK]

Donald,
It sounds like the upstairs room is just too tight and wont allow enough air in for it to draw properly ? When the upstairs one shuts off is the flame still blue or is it turning yellow ? If it is still blue then it should be getting enough air and maybe something else is wrong. Maybe time for a service call.

 

[Donald shaffer]

Caddybill Yes i do believe it is to tight for a good draw . 4" hole in wall 4 by 10 hole in floor but i still have to open door or window. And it does not matter if both or 1 is on.

 

[Donald shaffer]

BillK I don't no , it turns off and don't look until i feel the cold air ,will try today and keep a eye on it

 

[Caddybill]

there is a calculation do determine how much air is needed. Google "combustion make up air calculation". It's easy to figure out. You do have to take into account how much stuff is in the room as well. The formula assumes an empty room. Stuff takes up space and displaces air. So the room could be big enough, but if its packed to the rafters you will have a problem.

 

[Donald shaffer]

Caddybill Thank you very much. I will check out "combustion make up air calculation"

 

[chrispyny]

Get yourself one of those outside air kits for each heater. It draws cold air for combustion in and exhausts out the same opening. Tube within a tube. Not cheap but who cares if it will fix your problem.