Reznor FT45 fires, then stops- has new flame sensor

[highfigh]

I have used my Reznor FT45 for over ten years and until last Winter, it worked very well, but it stopped near the end of the season, so I didn't really need it. Trying to solve the problem-

Induction motor runs, spark ignition works, flame starts and shuts off after about 5 seconds. It makes several attempts.

I use YouTube for finding a lot of answers, but when I need a specialist, I ignore the "some guy who worked on one of these". The majority of the videos indicated that the flame sensor was a likely culprit and showed how to check the current but since they weren't specific to my model, they didn't state the required voltage on the wire for the sensor at the beginning or after the sensor has been immersed in the flame. Since the flame starts and since I have dealt with pressure switch issues in the past, I know this one is OK- it wouldn't fire if the switch or rubber line were bad.

When I measured Current, it read >5uA, which is in the 'acceptable' window, from what I have seen. I would like to find a more detailed schematic because the one on the cover seems to be somewhat different from my version- it shows hot surface igniter and mine is spark. The schematic I downloaded shows a momentary switch that can be pressed for >2 seconds, to show the most recent fault codes, but mine doesn't have this- it only has a pair of CIP switches. The

I do some woodworking in the garage, but I use a good dust collector and when I used a brush to clean the top of the heat exchanger, nothing came off and it's very clean with virtually no residue of any kind. I do have a small endoscope camera that I can insert, if needed.

I have always used a small Propane tank for fuel and it never failed, even though everyone said it wouldn't work- the photos show the stickers on the cover but I'll get a photo of the circuit board part number ASAP.

Do the relays fail in these? I had a furnace that was over-sized by a previous owner of my house and the relay had burned contacts, probably from short-cycling. It had four contacts, but only two had been used.

Thanks, in advance.

 

[fitter30]

Have u looked at the flashing lite on the burner module shows the failure. More than likely the cross over tube has some holes blocked or tripping on the roll out switch. Thats why the lite tell where to look first. If you pull the burners blow them out to.

 

[highfigh]

Have u looked at the flashing lite on the burner module shows the failure. More than likely the cross over tube has some holes blocked or tripping on the roll out switch. Thats why the lite tell where to look first. If you pull the burners blow them out to.

The LED flashes fast, but there's no change in the frequency- the panel shows that as meaning 'call for heat' but the manual I saw online mentioned a small momentary switch that should be pressed, so the most recent code(s) can be seen- mine doesn't have that kind of switch (could be rectangular, or square).



It's going to be cold for the next few days, but warmer next week- I'm going to make sure the heat exchanger is clear (can blow air into it) and as I posted, I have a small endoscope camera, so I can see if it's blocked from both ends. I'll also get some photos of the board, shine a light on the exchanger and use the scope to see if it's cracked or has holes, but it looks great from the outside. I may even install a pulley, so I can lower it and make this easier- I need to move my boat out to set up a ladder in order to check out the heater.

Thanks

 

[gmcgeo]

If it goes through the process, and turns off after 5 sec of flame. Then its in the flame / pilot / ignition / or gas issue. flame sensor could be faulty even though its new.

try cleaning it with steal wool.

If you do not let it try up to 3 times to start, then it will not throw a code.

Check your gas pressure from manifold. see what pressures you are getting. Could be low gas pressure shutting it down.

 

[fitter30]

Looking at your pics the first and last has different fault codes between the two. First doesn't have a fault for the roll out switches and shows a optional pressure switch. Last one also shows manual reset roll out switches. Flame rod will set a code after three trials. Put a meter across each safety at the burner control but first jump out the thermostat. Tap on burner control might have a bad solder joint on the board. Pull on every wire connection. Here's a manual.

Https://www.google.com/url?q=https://partner.reznorhvac.com/files/I-FTwCover_0.pdf&sa=U&ved=2ahUKEwjF5LfC_I38AhVoMDQIHQvQB4YQFnoECAMQAg&usg=AOvVaw0jVTuc5u1RQ2GNltej3SsK

 

[highfigh]

If it goes through the process, and turns off after 5 sec of flame. Then its in the flame / pilot / ignition / or gas issue. flame sensor could be faulty even though its new.

try cleaning it with steal wool.

If you do not let it try up to 3 times to start, then it will not throw a code.

Check your gas pressure from manifold. see what pressures you are getting. Could be low gas pressure shutting it down.

For clarity- I have worked with electrical/electronics for decades (including fuel injected engines) and when I see a problem, I want to check voltage, etc- When a part replacement without other data doesn't fix a problem, I automatically think "I have Voltage, but is it the correct voltage?" and that's one of the reasons I want to find a manual.

I have always let it try at least three times, but since there's no momentary switch to press, I don't know how to find the most recent codes.

 

[highfigh]

Thinking of getting one of these as a stop-gap measure, but I don't want it if it produces as much moisture as a torpedo heater. It would allow me to pull the Reznor down and service it.

https://www.menards.com/main/heating-cooling/heaters/gas-garage-heaters/mr-heater-reg-80-000-btu-portable-propane-convection-heater/f270490/p-1444441199579-c-6861.htm?tid=1027139842058517948&ipos=29

 

[gmcgeo]

rare you would have a voltage problem.

However once your done checking your voltages. move on to your gas pressures. and make sure burners are clean

 

[highfigh]

rare you would have a voltage problem.

However once your done checking your voltages. move on to your gas pressures. and make sure burners are clean

But if a relay has a burned contact or some other component fails, I could easily have a voltage drop. The tank is fresh, so the pressure shouldn't be an issue, but I don't have a way to test that, unfortunately.

This isn't an absolute necessity and with the cold snap, nobody in their right mind will show up for a garage heater service call, so I'll let it go for awhile.

 

[gmcgeo]

good luck

 

[D45]

Flame roll out sensors all good?

Hot Dawg 75K Fault Code

So, I went to turn my heater on this morning, just to make sure everything was good..........nope It turns on, fan blows, and no warm air I take off access panel and the LED has 3 flashes Any quick and easy ideas, that I can check myself?

www.garagejournal.com

 

[highfigh]

good luck

Thanks

 

[highfigh]

Flame roll out sensors all good?

Hot Dawg 75K Fault Code

So, I went to turn my heater on this morning, just to make sure everything was good..........nope It turns on, fan blows, and no warm air I take off access panel and the LED has 3 flashes Any quick and easy ideas, that I can check myself?

www.garagejournal.com

Haven't checked yet, but will when it's not so cold. Supposed to have mid-upper 40s in about a week. Still haven't seen anything other than fast flashes and can't check recent codes. Will access the switch ASAP.

 

[highfigh]

Just to have more info when I go out to work on this again:

the heat exchanger is a set of tubes that meet at a collector, right?
The roll out switches are normally open, or closed at room temperature? As long as I know which, I can test for continuity.

I don't have a manometer but I know someone who worked in HVAC, so I'll see if he still has one.

 

[fitter30]

Disconnect the flame rod see if it throws a code

 

[fitter30]

Then jump one safety at a time. Pressure switch will throw a code if it's made befor it should have.

 

[highfigh]

Thanks for these replies- this is the kind of info I have been looking for.

 

[D45]

Bypassing each rollout sensor is a good idea with a simple jumper wire

 

[highfigh]

I have plenty of test leads, so I'll do this soon.

 

[4x4Pete]

Rollouts and limits are normally closed at room temperature. Some rollouts and limits are manual reset. You can test with continuity tester on your meter. If you follow the wiring you can test from one end to the other to see how much resistance is there. Could be a few high resistance connections and not just the switches themselves. An open circuit in the rollout/ limit circuit will prevent firing. So if you're firing up then failing it probably won't be a limit circuit problem especially if it only runs for 5 seconds. Something else I have seen is paint inside the ventor assembly peel off and block the pressure switch tube, causing a intermittent failure. If yours isn't painted it's still a good idea to see whats up in there. Good luck!

 

[highfigh]

Rollouts and limits are normally closed at room temperature. Some rollouts and limits are manual reset. You can test with continuity tester on your meter. If you follow the wiring you can test from one end to the other to see how much resistance is there. Could be a few high resistance connections and not just the switches themselves. An open circuit in the rollout/ limit circuit will prevent firing. So if you're firing up then failing it probably won't be a limit circuit problem especially if it only runs for 5 seconds. Something else I have seen is paint inside the ventor assembly peel off and block the pressure switch tube, causing a intermittent failure. If yours isn't painted it's still a good idea to see whats up in there. Good luck!

This is the kind of info I have been looking for and Reznor's phone message just tells people to contact their local dealers/servicers. If we weren't in the middle of a cold snap, that would be much easier but again, it's not for my house, so there's no rush.

I have worked as a boat service tech and trained on fuel injection- I know how to troubleshoot that but knowing what to look for WRT HVAC is out of my range of past experience, other than the pressure switch issues in my furnaces.

 

[highfigh]

Well, my Reznor is working again. I started by replacing the flame sensor last Spring, then pulled the wires back or off of the rollout sensors a few weeks ago and also connected jumper wires. Those weren't shorted or non-functioning, so I checked the exhaust to look for blockage at the elbow near the heater and removed everything before the stack and looked up to the top, seeing nothing in the way. Next, I used my blow gun to remove anything that could have been on the heat exchanger- still nothing. I looked at the flame going into the heat exchanger and after shutting the heater off, blew air into the tubes. I think something must have clogged the ends slightly, but enough to cause the rollout sensors to register it as a problem. Next time I turned it on, it worked. I let it cycle a few times and it's still working.

It's great to have heat in the garage again- thanks all, for the info.

 

[rags260z]

Sorry to bring this thread back from the dead, but I'm experiencing the same symptoms with my ft45. Where exactly was the last place you hit with pressurized air? I don't want to replace the unit as it has worked flawlessly for me up until yesterday.

Thanks

 

[highfigh]

Sorry to bring this thread back from the dead, but I'm experiencing the same symptoms with my ft45. Where exactly was the last place you hit with pressurized air? I don't want to replace the unit as it has worked flawlessly for me up until yesterday.

Thanks

I blew dust out as a general cleaning measure but I had also removed the flue from the heater to the stack, just to see if something had built a nest inside but it was clear, so I blew air into the heat exchanger from the end where the jets are located. I really didn't see what came out, but it started working immediately after and it has been working great since I did that. If the compressed air hadn't worked, I was going to insert my inspection camera and look for anything that could be blocking it.

Before I used compressed air, I slid the wires off of the rollout sensors and measured for continuity- they were all OK, but I don't really have a way to know if moving the terminals made a clean connection or not because I didn't check each wire beforehand. Since none of the wires or terminals have visible damage, I doubted that would have showed anything.

 

[theoldwizard1]

Similar problem, different furnace. After firing the parts canon, it was the gas valve (?).