I have a bunn CW series brewer. I filled the reserve with water and allowed to get hot. I then add additional water (1 glass pot) and it just starts to dispense without me hitting the "start" button. I also noticed that when I hit the "start" button I don't hear anything that would engage the machine. Could the switch be bad? What would cause the machine to just dispense water when I add that additional pot?

Sorry this brewer is usually set up for a full pot brew. I have reset this for a small (but not half) pot brew as the customer wanted to use a metal carafe (with their own logo). I also tried once to get it to half pot brew but it can get tricky if you actually brew twice to get a full pot (in the same pot).
* there is a siphon action that starts once the boiler tank gets filled to a certain point. From that point it will continue to flow until the boiler is emptied to the level that stops the siphon action and leaves enough water in boiler to reheat for the next brew. Achieving the siphon point may be a larger volume of water for 1/2 a pot but may work for 3/4ths a pot. The 1/2 way mark may be affected by the brewers "level" while placed on a table or sagging in the middle of a weak table.
* Usually if you want a smaller brew then go with a smaller brewer. Though there is a hot water tap that will give you 2-4 cups of hot water (it gets tepid after that) which you can use for the "Mug" style brew. But it does get messy.ukeboy57
* Final, If you don't mind a little more than 1/2 pot brews then ask your vendor to adjust the machine for you. Though a reminder NOT the double brew in the same pot as it will overflow.
Aloha, ukeboy57

VPS/VPR are pour over brewers. Like the 12 cup brewers you find at home, they need to be filled with 12 cups of water (a full pot), heated and then peculated over the coffee grounds and collected in a decanter.
BUT there is one main difference! The VPR and similar COMMERCIAL coffee machines are quick brewers. They usually have a pre-heated pot of water stored inside the machine.
* VPR's and similar machines REQUIRE a pre-fill and heating period prior to brewing. This means it's sitting on a level table and filled with water until water sprays from the brew head. At this point the unit is plugged in and the heater is turned on (there may be some water discharge from brew head as the water expands). Ready light will come on in about 15 mins.
* To Brew; Place coffee grounds in filter, place in funnel and brew head, clean empty decanter under funnel, slowly pour one full decanter of water (cold or hot) into brew tray. Do not overflow tray. Allow water level to sink before adding more water. Only fill with one pot as an equal amount will come out the brew head and funnel.
* Make sure the decanters are all the same size. do not mix a 12 cup pot with a 10 cup pot. One will over fill and the other will under fill. Make sure they match (in cup volume) FYI; Thermo Air pump pots are usually bigger than one pot. Typical filling only to 3/4th of the container. (I think most are in 2.5 to 3 liter sizes)
* If your not getting a full pot then the brewer was partially empty. The second brew (if done within the next hour) should come out full.
* If your still not getting a full pot then the water is leaking or is boiling off. Does it always steam from the top? Thermostat is shorted. Unplug the brewer and call vendor for service.
* Final; If your unplugging when not in use. Then follow the Pre-heat instructions mentioned above prior to plugging the brewer back in. If the tank has been emptied at night or dried up after an idle week. Then there is a chance you may over heat and blow the thermal fuse. Or at best have a half pot short brew as the water dried up.
* Note leaving the brewer plugged in without brewing daily is not a good idea. The water evaporates and eventually drys out the pot. Takes about 1-2 weeks but it does blow the fuse(s) and the unit will need service.
* Final; Follow the Bunn set up and care instructions (manuals from Bunn.com for down loading. *FREE*)
Aloha, ukeboy57

VPS are pour over brewers. Like the 12 cup brewers you find at home, they need to be filled with 12 cups of water (a full pot), heated and then peculated over the coffee grounds and collected in a decanter.
BUT there is one main difference! The VPR and similar COMMERCIAL coffee machines are quick brewers. They usually have a pre-heated pot of water stored inside the machine.
* VPR's and similar machines REQUIRE a pre-fill and heating period prior to brewing. This means it's sitting on a level table and filled with water until water sprays from the brew head. At this point the unit is plugged in and the heater is turned on. Brewer will pre-heat the water (there may be some water discharge from brew head as the water expands). Ready light will come on in about 15 mins.
* To Brew; Place coffee grounds in filter, place in funnel and brew head, clean empty decanter under funnel, slowly pour one full decanter of water (cold or hot) into brew tray. Do not overflow tray. Allow water level to sink before adding more water. Only fill with one pot as an equal amount will come out the brew head and funnel.
* You can test the VPR by following the Pre-fill instructions I've listed earlier. If the brewer heats up and does not continuously boil (shorted condition) then try a brew. If it works then your okay. Otherwise the unit will need service for a blown high limit or bad heater element.
* Call your coffee vendor anyway. Many coffee vendors will service your brewer of even replace it as long as you buy coffee from them. Ask around.

Aloha, ukeboy57

* If this is a pour over (VPR, VPS, etc.) then you must pre fill it then pour in one pot of water to get one pot of brewing hot water out of it.
* If this has an external tank of water then it must be filled and make sure the float sensor works and pops up to indicate a filled tank.
* But most likely this is a CWTF, CW, or larger commercial brewer that has a plumbed in water line. If this is the case then the tank must be pre-filled and heater turned on. usually done by the vendor or installer. It should have been tested and brewed to check water level of brew. Follow the brewing instructions.
* Still not working? Call vendor for service. It could be timer, brew switch, water level board, water fill valve,brew valve. all need check and service to replace as needed. Many larger units have high voltages so call the tech to be safe.
Aloha, ukboy57

Have you cleaned lately, put in an empty filter and fill with cold water with a tablespoon of white/clear vinegar. Run the brew cycle, empty pot and while still worm fill with cold water again with out vinegar. Than check filter to see how much hard water chunks are in the filter. Repeat with and without vinegar tell filter is clean. One question though is there a lot of steam coming out of the top during the brewing cycle if so inside there is a tube that may be cracked, broken or came loose, have to look inside. requires opening or disassembling unit to check. REMEMBER when taking apart UNPLUG unit first.

Sounds like the switch is stuck in the operate position. Therefor once the machine hits temperature it just brews. Your local Bunn distributor should be able to recommend an engineer to replace the switch or supply the correct t,hope of switch if your confident enought Tom replace it yourself.

The A10 has a semi-sealed tank that keeps +1 pot of water heated and ready to brew. Pouring in a full pot of cold water will fill the top tray and allow a slow trickle of cold water into the top which forces hot water to over flow into the brew basket. This continues until all the cold water drains into the heater tank. So the brew is matched volume per volume. UNLESS the tank was empty or not filled prior to brewing. Follow the brewing instructions from Bunn (on line for *FREE* download at Bunn.com)
* If it leaks (from the bottom) only when you pour in water. Then your pouring it too fast and over flowing the fill tray. slowdown, watch the level in the tray. do not fill past the lid.
* If it leaks just sitting (not brewing) then there is a hole in the tank. Call for service.
* If it leaks after filling the tray half way. then the top of the tank has a leak, loose, cracked, or missing gasket. There is quite a few gaskets on the lid. Call for service.
* Final; Leaks are always bad around electrical equip. Best to unplug and call for service to be safe.
Aloha, ukeboy57

PS. Check your using the correct size decanter for this brewer. If it's a 10 cup brewer then make sure all the decanters in the office is also 10 cup. Pouring a 12 cup pot into brewer will have 12 cups of coffee come out (over flowing the 10 cup pot.) Note that not all decanters are made the same size. Other brands may be different. Test by filling a pot with water (from faucet) then pouring directly into pot in question. It should match and not under fill nor over fill.

* Check bunn.com for a free download of manual for this brewer.
* If this is a pour over (VPR, VPS, etc.) then you must pre fill it then pour in one pot of water to get one pot of brewing hot water out of it.
* If this has an external tank of water then it must be filled and make sure the float sensor works and pops up to indicate a filled tank.
* But most likely this is a CWTF, CW, or larger commercial brewer that has a plumbed in water line. If this is the case then the tank must be pre-filled and heater turned on. (a switch in the back) Installation is usually done by the vendor or service tech. It should have been tested and brewed to check water level of brew. Follow the brewing instructions.
* Still not working? Call vendor for service. It could be timer, brew switch, water level board, water fill valve,brew valve. all need check and service to replace as needed. Many larger units have high voltages so call the tech to be safe.
Aloha, ukboy57

VPR is a pour over "Volume Displacement" brewer. Required to completely fill the inner tank and heat prior to using brewer. BEFORE plugging in unit, water must be poured into upper tray and with brew funnel and empty pot in place. Keep pouring water into top fill tray until water drips out of brew funnel. Plug in VPR and allow it 15-20 mins to heat up. leave the pot as there may be additional water dripping. Remove power if there is any water spilling out from other places like the top pan cover or bottom of machine. With the initial heating done, take a full pot of water and slowly pour into the top filling tray. HOT steaming water should come out of the brew funnel to fill the (empty) pot. Prep is done and the machine can be used to brew a pot after 10-15mins of reheat time.
*** the machine you have needs to be checked for leaks in areas mentioned above. Water should only come out of brew funnel (if not present then the brew head or if that is missing then the brew pipe. All will need to be replaced prior to brewing.) Leaking under machine is an indication of leak(s) in pour tray,tank,tank cover, gasket, probe gasket. This machine like any used equipment should be checked out by qualified tech prior to use. Be aware that coffee vendors sometimes rent or loan brewers to customers.

The procedure for setup of this coffee maker can be found here -

http://www.bunn.com/pdfs/commercial/manuals/10613.0000.pdf

Please email if you have additional questions.