The third thing to check is the flow gauge. It normally sits below a temperature gauge. You can see here at the top of the glass section L/MIN. That stands for 'litres per minute' i.e. how fast the fluid is flowing around your system when the pump is working.

When the pump is running, you should see in the window a small plastic float gently bobbing around (often a white or off white colour). When working correctly, i.e. when the fluid is flowing as it should, the bottom of the float generally sits between 3 & 5.

If the pump is running and, like here, NO float is visible then there is no flow in your system. Time to call someone to get it fixed.