Reznor FT45 High limit code.

[armstrong20]

I replaced the fan motor last year and had to clean out a clogged vacuum line and replaced high limit sensor last month. The high limit open code is back. The heater will cycle back on, reignite and run after it drops it's flame. My question is this: what are the odds I purchased a defective high limit sensor or am I missing something?

 

[PoorUB]

Check over the heat exchanger well. I have seen FT's with rotted out heat exchangers that will run, but trip the high limit becuase the inducer doesn't pull the flame through the heat exchanger as well as it should with the holes in the heat exchanger.

 

[gmcgeo]

What PoorUB said. look at the heat exchanger

 

[armstrong20]

Ya, I examined the heat exchanger a couple time and it appears okay although it's showing it's age by turning white. I have also cleaned the flame roll-out sensor as well and it looks great? After it cycles and relights once, it runs fine and cycles okay most times except when it doesn't? Maybe it is the exchanger but I can't see it? Thanks everyone!

 

[gmcgeo]

Ya, I examined the heat exchanger a couple time and it appears okay although it's showing it's age by turning white. I have also cleaned the flame roll-out sensor as well and it looks great? After it cycles and relights once, it runs fine and cycles okay most times except when it doesn't? Maybe it is the exchanger but I can't see it? Thanks everyone!

vent clogged?

 

[PoorUB]

That would be the next thing to check. B-vent? It rots out too and chunks fall and restrict the flow of the exhaust. No cap on the end? Bird's nest!

My furnace in may garage is vented straight up with B-vent. A couple winters ago I was having trouble with it and took a look inside the vent. I was surprised it even ran. The inner liner was about 90% gone and what was left had fallen down and blocked the vent. I can see why they vent shop heaters with stainless!