I had the similar problem and fixed it through removing the nozzle at the front and cleaning it out. There were leaves and dirt stuck in there, and once cleared it worked perfectly once again. Make sure there’s not dirt or debris stuck elsewhere in the canister.
Another potential fix is to remove the air filter between the handle and the canister, shake it out (or wash, wring, and air dry it completely), and then flip it top to bottom so the tab at the opposite end is facing down (the side tab and “faucet” graphics will still face out as before). This didn’t solve my problem but might fix yours.
A third possible fix is to replace the battery. However this is a costly replacement, and my battery has lasted many years without any problems, so make sure you follow other troubleshooting tips first.
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=== Update (11/21/2018) ===
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Another helpful resource is this video guide to disassembly and cleaning of the DC56:
I had the similar problem and fixed it through removing the nozzle at the front and cleaning it out. There were leaves and dirt stuck in there, and once cleared it worked perfectly once again. Make sure there’s not dirt or debris stuck elsewhere in the canister.
Another potential fix is to remove the air filter between the handle and the canister, shake it out (or wash, wring, and air dry it completely), and then flip it top to bottom so the tab at the opposite end is facing down (the side tab and “faucet” graphics will still face out as before). This didn’t solve my problem but might fix yours.
A third possible fix is to replace the battery. However this is a costly replacement, and my battery has lasted many years without any problems, so make sure you follow other troubleshooting tips first.