Water tank level indicator sinks to the bottom when water tank is full.

Check the float in the tank, if it is not floating up from the bottom then jam something plastic underneath it to activate the water level sensor. You can either continue to use it like that ans check water level before you brew or buy a new tank, there is no repair for a float.

Check the float in the tank that indicates the water level to the sensor. They often fail to float, solution is to either replace the tank or jam something plastic under the float to lift it to the top of its slot.

The sending unit is located in the fuel tank of the car. It consists of a float, usually made of foam, connected to a thin, metal rod. The end of the rod is mounted to a variable resistor. A resistor is an electrical device that resists the flow of electricity. The more resistance there is, the less current will flow. In a fuel tank, the variable resistor consists of a strip of resistive material connected on one side to the ground. A wiper connected to the gauge slides along this strip of material, conducting the current from the gauge to the resistor. If the wiper is close to the grounded side of the strip, there is less resistive material in the path of the current, so the resistance is small. If the wiper is at the other end of the strip, there is more resistive material in the current's path, so the resistance is large When the float is near the top of the tank, the wiper on the variable resistor rests close to the grounded (negative) side, which means that the resistance is small and a relatively large amount of current passes through the sending unit back to the fuel gauge. As the level in the tank drops, the float sinks, the wiper moves, the resistance increases and the amount of current sent back to the gauge decreases. This mechanism is one reason for the inaccuracy of fuel gauges. You may have noticed how your gauge tends to stay on full for quite a while after filling up. When your tank is full, the float is at its maximum raised position -- its upward movement is limited either by the rod it's connected to or by the top of the tank. This means that the float is submerged, and it won't start to sink until the fuel level drops to almost the bottom of the float. The needle on the gauge won't start to move until the float starts to sink.

Something similar can happen when the float nears the bottom of the tank. Often, the range of motion does not extend to the very bottom, so the float can reach the bottom of its travel while there is still fuel in the tank. This is why, on most cars, the needle goes below empty and eventually stops moving while there is still gas left in the tank.

Inside the water tank there is a magnetic float which is causing the problem. This float is moving always on the top of the water tank as you fill it with water and in reverse as the water level goes down then the float is moving down to bottom also. So as the magnetic float is moving up and down is giving the signal for the water level if it is full or empty.
So possibly now the float is stuck in the bottom and even if you have refill the tank this is still on the bottom of the tank. This can happen from many reasons. First could be that the plastic column that the float is moving is full of scale and it can not move up and down freely any more so you can clean it from scale by decaling it and even clean it with a wire brush.
A second possibility could be that float have a tiny hole and some water enter in the float and this make it to stay on the bottom of the tank. You can visually inspect it and if possible you can dry out the water and weld with a super glue the hole if possible, if it can not be fixed then you need a new float.
If you wand to fix it temporary until you find a new float you can a plastic clip or similar to secure it always on the top however you when the tank is empty it doesn't register so you would really have to keep an eye on the water level to avoid any other problems with the machine.
Good luck

http://www.shop.partsguru.com/145500859-Saeco-level-float-Sold-with-cover-145500859.htm?categoryId=-1

Open the hot water valve, and run about a cup of water, this will engage the pump and fill the circuit.

The problem is with the sensor inside the gas tank since the method of indication used is by passing an electric current & the resistance to that current is a measure of level of liquid in the tank , i.e. the gauge consists of two parts:

• The sensing unit
• The indicator

The sensing unit usually uses a float connected to a potentiometer. As the tank empties, the float drops and slides a moving contact along the resistor, increasing its resistance. In addition, when the resistance is at a certain point, it will also turn on a "low fuel" light on some vehicles.
However if this float gets stuck to the bottom of the tank or a leak fills up the float making it sink to the bottom of the tank, thus always indicating 'E' for empty.........................sodeep

OK, first of all, I do not recommend my solution if you are forgetful or do not check your water level manually daily.

However, I found a super easy solution.

The way the unit works is to use a float in the water chamber with a magnet on the bottom. When their is enough water in the tank, the float rises and the magnet on the bottom floats to the top of the magnet chamber. When it floats up, it aligns with a sensor in the machine that allows the machine to operate. When the the water level lowers, so does the magnet and drops below the internal sensor disabling the machine with a "Fill Water Tank" error message.

To eliminate this error and allow the machine to operate, I simply popped off the lid to the magnet chamber with a butter knife and turned the water chamber up side down to let the magnet float fall out. Remember to empty the water first.

Here comes the highly technical part. Turn the magnet float upside down and slide it back into the float chamber. Since the actual magnet is on the bottom of the float it now is at the top allowing the internal sensor to turn off. No more error message!

The reason I do recommend this is because this completely defeats the purpose of the sensor and will most likely damage your machine if you run it without water. Keep you tank filled however and you will eliminate the frustration of a "float gone bad" keeping you from your morning caffeine.

Inside the water tank there is a magnetic float which is causing the problem. This float is moving always on the top of the water tank as you fill it with water and in reverse as the water level goes down then the float is moving down to bottom also. So as the magnetic float is moving up and down is giving the signal for the water level if it is full or empty.
So possibly now the float is stuck in the bottom and even if you have refill the tank this is still on the bottom of the tank. This can happen from many reasons. First could be that the plastic column that the float is moving is full of scale and it can not move up and down freely any more so you can clean it from scale by decaling it and even clean it with a wire brush.
A second possibility could be that float have a tiny hole and some water enter in the float and this make it to stay on the bottom of the tank. You can visually inspect it and if possible you can dry out the water and weld with a super glue the hole if possible, if it can not be fixed then you need a new float.
If you wand to fix it temporary until you find a new float you can a plastic clip or similar to secure it always on the top however you when the tank is empty it doesn't register so you would really have to keep an eye on the water level to avoid any other problems with the machine.
Good luck