What's new
By:
Filters

Reznor F75 heater issues

NDCjeepsmith

NDCjeepsmith

Red Skull Member
Joined
Dec 8, 2021
Member Number
4600
Messages
655
Loc
SW Mo
Have a Reznor F75 from 1994 that won't kick on. I'm assuming it's a safety switch but there's no diagram or any numbers on anything I'm seeing.

I have power to transformer and measured 30V coming from transformer (thought they were 24V though)....

What is the switch below the transformer? I got 0V on one set of terminals and 3V on the other.

20221220_111710.jpg
20221220_110802.jpg


I'm assuming since the tstat wires go to that switch it tells transformer to kick on and power the unit?

I have a pilot light but once it's going and tstat is turned up, nothing kicks on.
 
Maybe it's tstat cause I get no voltage at those wires leading into the switch...???
 
30V measured here
20221220_111710.jpg


0V between center and right terminals...

Where to test next?
 
30V at these two wires on gas valve but only when disconnected. If connected and test the screws on terminals there's nothing.

20221220_120343.jpg


They come from the circular white plug above the red circle drawn.

20221220_111710.jpg
 
Check continuity on any thermostat, switch, over load or high temp kick out
I'd check continuity on the coil and voltage to ground
 
Did you get this fixed? I would find where this yellow wire is going and check continuity across safeties, and/or push the reset on them if applicable, it eventually turns into the black wire going to GV if I’m seeing it right. The transformer output is going to be closer to 30v as you see, will be ~24v under load.

36544103-FA73-41F7-9DD7-EE630CCD5AB6.jpeg
 
Last edited:
No not fixed, picked up another LJ and been assessing that and it's been unusually cold here so with Xmas off I've been lazy. Thanks for input tho. I'll check that out. I'm thinking it's a safety inside too
 
The yellow you circled goes up to top of unit where it and another yellow go into the inside. I'm assuming one of the safety switches. Everything with two wires that comes out of unit tests good continuity wise so I'm leaning towards valve now.

Is a GV testable off the unit with no gas flow? Also what's the difference between this unit run on natural gas and ran on propane? Can it be run on propane, would it need a different valve or are they interchangle?
 
It’s hard to bench test a GV with a pilot because applying 24v to valve without pilot heating thermocouple isn’t going to open main valve.
If you take power from the blue wire on terminal strip and apply it where black is on valve you will be ruling out all safeties.

I mainly check safeties with power on because showing continuity on a meter doesn’t necessarily mean you have the ability to carry current. Likewise showing 30v at the valve doesn’t necessarily mean you have the current needed to open valve. If you truly had power there it should show voltage with wires plugged in as well as unplugged.

To run on propane you need a conversion kit which consists of new orifices for main burners and pilot as well as a new spring for gas valve regulator.
 
So Reznor 99245 nat to LP conversion is listed but all I see is out of stock, discounted, or unavailable so if I got one of these for free to put in shop it wouldn't even be worth the hassle huh?
 
Jumping that blue to the yellow on terminal strip rules out thermostat btw.
 
Idk. Maybe just a bad connection at a terminal. Plugged everything back in and it's staying going. Fan does only run for like 10 secs then kicks off, then back on. I've got Tstat all way up at 80 but it may be warm enough in here now to not need heat so I'll recheck it when temp drops.
 
You must log in or register to reply here.
Top Back Refresh