Bunn coffeemaker starts before water completely in reservoir

If you're talking about the model shown in your picture, the leak is most likely between the water reservoir and the tank. Bunn uses a soft silicone seal for that connection that gets compressed over time and starts to leak water whenever you make a pot of coffee.

It's planned obsolescence. Bunn won't sell you a new seal. So you have to improvise. But it's simple enough to do.

Remove the top cover and the plastic water reservoir right below it. Don't tamper with the little valve that opens when you close the lid.

Look for the seal. It could be stuck to the bottom of the reservoir, or sitting loosely on top of the metal tank. Make sure to preserve its top-to-bottom orientation (don't put it back in upside down).

Apply a narrow bead of clear silicone into the grooved side of the seal. Press the seal gently onto the reservoir, then apply a thin layer to the smooth side.

Re-install the reservoir and reassemble the unit.

The leak is most likely between the water reservoir and the tank. Bunn uses a soft silicone seal for that connection that gets compressed over time and starts to leak water whenever you make a pot of coffee.

It's planned obsolescence. Bunn won't sell you a new seal. So you have to improvise. But it's simple enough to do.

Remove the top cover and the plastic water reservoir right below it. Don't tamper with the little valve that opens when you close the lid.

Look for the seal. It could be stuck to the bottom of the reservoir, or sitting loosely on top of the metal tank. Make sure to preserve its top-to-bottom orientation (don't put it back in upside down).

Apply a narrow bead of clear silicone into the grooved side of the seal. Press the seal gently onto the reservoir, then apply a thin layer to the smooth side.

Re-install the reservoir and reassemble the unit.

The leak is most likely between the water reservoir and the tank. Bunn uses a soft silicone seal for that connection that gets compressed over time and starts to leak water whenever you make a pot of coffee.

It's planned obsolescence. Bunn won't sell you a new seal. So you have to improvise. But it's simple enough to do.

Remove the top cover and the plastic water reservoir right below it. Don't tamper with the little valve that opens when you close the lid.

Look for the seal. It could be stuck to the bottom of the reservoir, or sitting loosely on top of the metal tank. Make sure to preserve its top-to-bottom orientation (don't put it back in upside down).

Apply a narrow bead of clear silicone into the grooved side of the seal. Press the seal gently onto the reservoir, then apply a thin layer to the smooth side.

Re-install the reservoir and reassemble the unit.

It is part of the rocker arm. If you will call customer service with the model and date code, we will be able to help you resolve this problem. The number is 800-352-2866.

Empty the water reservoir and put back on the side of the coffee maker. Put your hand in the reservoir and slide the disc that monitors the water level back toward the top and and hold in that position,the machine will think there is water. Then put a cup under the head and select a cup. The water will come out. You must hold the disc up inside the reservoir to continue to get the water out.
Here is another tutorial : http://www.ehow.com/how_5849515_drain-reservoir-bunn-coffee-maker.html

Make sure all hinges & covers are correctly on!

From the manual I found online here.
CLEANING AND MAINTENANCE COMPLETELY CLEAN AND DRY ALL PARTS AFTER EVERY USE. Always turn coffeemaker OFF and remove the plug from the electrical outlet before cleaning. Open the reservoir lid*. Remove the grinder basket lid by using the recessed area on each side of the lid. Then remove Grinder Basket. Open Filter Basket Door. Remove Filter Basket Cover, Filter Basket and Filter Basket holder. The grinder basket, grinder basket lid, filter basket and filter basket cover can be washed in warm soapy water and rinsed thoroughly, or cleaned in the upper rack of the dishwasher. Dry all parts after every use. Do not put any water in the unit once the grinder basket has been removed. Wipe the area under the grinder basket with a damp cloth. If water gets into the grinder motor, the motor may become damaged and may malfunction.
DECALCIFICATION Decalcification refers to removing the calcium deposits which form over time on the metal parts of the coffeemaker. For best performance from your coffeemaker, decalcify the base unit from time to time. The frequency depends upon the hardness of your tap water and how often you use the coffeemaker. To clean, fill the water reservoir to capacity with a mixture of 1/3 white vinegar and 2/3 water. Turn the coffeemaker on by pressing the ON button. One cycle should be sufficient to adequately clean the coffeemaker. When the cycle is completed and the five beeps sound, turn coffeemaker off. Repeat operation, this time using fresh cold water.

before plugging in place your empty filter basket in the coffee maker and place a pot under it. Slowly pour in two pots of water using the pour pitcher. Now you can plug it in. it'll take 15 min to heat up first time . when you brew your first pot leave your water level a little short,because the water will expand (only the first time)

The easiest way to empty these brewers is to turn them upside down over the sink. Turn it on it's side, always keeping the fill hole down toward the sink, and keep on going until you have the unit completely upside down. If there is a push switch under the lid to stop water from going into the pot until the lid is closed, you will have to keep this pushed in until the unit is empty

The Bunn coffee machine has an internal tank used for holding approx three potfulls of water at just below brewing temperature. When you add water for a potful, the thermostat senses cold water and starts the brew heater. The water level inside the tank comes up and goes through the sprayhead. This "surge" of water, that you call drips is normal. The hot water stratifies to the top of the tank, just like an electric water tank in a house. The internal pot heater kicks in and boils the water already in the tank, raising the water level in the siphon pipe to the sprayhead until the reservoir under the add water opening is empty.