Getting warmer

I've made some progress on my hot tub issue. I found that the water will heat, but only if I run the high speed blower. Troubleshooting with that information revealed the culprit is likely dirty and/or clogged filter cartridges. I tried cleaning the old filters, but it didn't solve the problem. Filters are only supposed to last 1-2 years. I don't know when the previous owner (my brother) last purchased new filters, but judging by their appearance, it was likely a long time ago. I ordered new filters tonight, and I will be very eager to put them in place to see if that solves the problem. We'll see, and I will let you know.