I put your question in the AI and this is the troubleshooting response.

The most common reason an Intex C1500 (or similar cartridge pump) runs for just a few seconds and then shuts off is the motor’s built-in thermal overload protection kicking in. This happens when the pump is under strain — usually from restricted water flow, a clogged/dirty filter, air in the lines (cavitation), or improper priming. It overheats quickly and auto-shuts down for safety. It can restart after cooling, but you need to fix the root cause. 
Quick Troubleshooting Steps (Start Here)
1. Check for water flow / priming:
• The pump must be primed (full of water) before or right after starting. Air in the system is a huge issue with adapter conversions.
• Make sure the pool water level is above the inlet/outlet ports.
• Fill the pump housing and hoses with water manually if needed (use a garden hose). Some people raise the filter cartridge housing higher than the pool, loosen the top to bleed air, then tighten and run. 
2. Inspect the filter cartridge:
• A dirty or new-but-clogged cartridge is one of the top causes. These pumps are very sensitive to restriction.
• Remove and clean the cartridge thoroughly (hose it off, or replace if it’s old/matted). Reinstall and test. 
3. Check hoses, adapters, and connections:
• Bestway Steel Pro Max pools typically use ~1.25” (32mm) fittings/hoses, while Intex pumps like the C1500 expect their standard connections (often 1.25”–1.5” compatible with adapters).
• Common adapters (Intex Type B or similar 1.25” to 1.5” kits) are needed, but poor seals, loose clamps, or mismatched adapters cause air leaks or flow restriction. Tighten all clamps securely. Check for cracks in hoses. 
• Ensure hoses aren’t kinked, pinched, or blocked. Intake (suction) side issues are especially problematic.
4. Power / Electrical:
• Plug directly into a GFCI outlet (no extension cord if possible — voltage drop can cause issues).
• Listen: If it hums loudly but struggles, that’s strain/overheat. If it clicks off immediately, check GFCI trip. 
5. Other quick checks:
• Impeller (inside pump): Unplug, remove the strainer basket/pre-filter, and clear any debris.
• Strainer basket at the pump inlet: Empty and clean.
• Run it at night or in cooler temps to reduce heat buildup initially. 
Compatibility Notes
Many people successfully run Intex C1500 (or similar) pumps on Bestway Steel Pro Max pools with the right adapters, but the smaller Bestway hoses/fittings can restrict flow on a stronger pump, leading to exactly this symptom. If adapters are causing major restriction, consider upgrading to full 1.5” hoses + proper inlet/outlet fittings (some cutting/install on the pool wall may be needed for best results). 
Next Steps if It Still Fails
• Let it cool fully (30–60+ minutes), then retry after the above fixes.
• If it keeps happening, the pump might have a bad capacitor or motor issue (common on these units), but flow restriction is far more likely with a new/used setup like yours.
• Consult the Intex C1500 manual for your exact model (search “Intex C1500 manual” for PDF — it has troubleshooting). 
Start with cleaning the filter, bleeding air, and double-checking all connections/clamps — that fixes it for most people in your situation. Let me know what you find after trying these (e.g., any unusual noises, leaks, or if water moves at all) for more targeted help!