If you have a Bissell carpet cleaner that won’t spray, the heater core might be clogged up. Start removing screws and parts (you can probably find a video on YouTube for your model) until you find a rectangular metal part with wires and hoses connected. For this model it turned out I didn’t need to take the handle pieces apart.
After you remove the wires and hoses, you should be able to pull the heater core out.
Then you can pop off the cover and clean out the inside. I should have taken a picture of the junk that was caked in the channels, but this is what it looked like after I did a quick cleaning.
Then comes the fun part of trying to fit everything back together. 🙂 I had to do it twice because I didn’t route some of the hoses properly. The unit works again though!