I have an older Johnson Furnace Co furnace in one of my units, I recently have a problem with the heat. It seems to go through the process with spark and fan etc but it won't light. It's an older model 48 HWC. Where would I start to testing this unit? And if I were to find the issue would parts still be available?

48000 BTU
M-48
S-K6

If the spark lights a pilot & the pilot lights the main burner, the pilot orifice is likely clogged. You will need to remove the pilot burner & clean the orifice. Spiders commonly build nests in them & block the gas flow.

The pilot doesn't light, I do see sparking but no flame. I took off the flame sensor to clean as well as the pilot orifice. I will install them back into the furnace today to see if that helps but if the pilot doesn't light, where would I try next? Thanks

Thank you, the pilot doesn't light. I did remove the flame sensor and pilot tube to clean and will install back into the furnace today. As mentioned I do hear and see sparks but no lighting at the pilot. Where or what would I test next?

Did you remove the pilot orifice & clean it? If not, you need to do so before reinstalling. Dirty pilot orifices are the #1 cause of the problem you are having.