Dear folks, I bought the house with a nice pool, but as a first time pool owner, I had no idea what everything was supposed to be. It turned out the entire in-floor cleaning system was not functioning. 0 out of the 15 pop up head works. 1 was missing. I bought a new one, but still couldn’t figure out why none of them works. The filter was cleaned, baskets emptied, caretaker opened, cleaned and checked, new o-rings were installed, no visible leak. I even dug out the dirt around the 5-valve and checked all 5 pipes. No leak at all. The only place I can’t check is under concrete plates. The pressure of the filter is relatively high, 20-25 psi, when returning to SPA, 20 psi, returning to pool pop up, 25 psi. Check valves all work. I feel the last chance is all the 5 pipes are clogged, but would it be possible? Hope to hear some suggestions from kind folks here. Thanks.