A toilet that won’t flush without a clog likely has low tank water level a broken flapper chain or a malfunctioning flush valve. Check the tank water level ensuring it reaches one inch below the overflow tube. Reconnect or adjust the flapper chain allowing slight slack. A warped flapper doesn’t seal properly and needs replacement. Mineral deposits on jet holes under the bowl rim reduce flushing power. Clean rim holes with a wire or vinegar soak.