My inkjet printer won't print blue

I'm not 100% sure about this particular model, but Canon and Epson printers (unlike many HP models) do not have the printhead integrated into the cartridge, opting instead to use a long-life printhead built into the printer (or a removable, but separate piece on higher-end printers) Printheads sometimes clog badly. Cleaning and "deep cleaning" works by forcing ink through them, in an attempt to dislodge the clog. This doesn't always work, and uses a ton of ink. The fact that it happened after changing the cartridge is likely a coincidence (or the first cartridge you used could have indeed been somehow bad and damaged the printhead). Summary: You may need a new printer.

http://www.metafilter.com/user/49429, the MP150 cartridges have an integrated print head, unlike most of the higher-spec Pixma printers. It keeps the price of the printer down on the budget models.

How old is your replacement cartridge? If you've had it sitting around for a few years it may have dried out.

doctor_negative: It's brand new - just delivered yesterday. The company I bought it from will happily replace it, but obviously I want to try to figure out what the problem is (and whether it's something at my end) before sending it back to them. le morte de bea arthur : I've checked carefully and there doesn't seem to be any extra sticker or anything like that. You're right that the logical conclusion is that it's the new cartridges. I guess that's most probably my answer; perhaps I got sent two from a faulty batch or something like that!

Make sure that you are using a CLI-8C cartridge, not a CLI-8PC, which is the "photo" version. It's the same size and looks the same, but won't work with the MP510 - believe me, I tried! :)

Oops, just realized you are using an MP150, not MP510, so ignore that last post. But do double check that you have the right model cartridge, as they can be very tricky.

One of the many tricks I learned in the digital print reproduction trade... Printers print heads, be they integrated into the ink cartridge or into the cartridge carriage (as mentioned by SCMOD) dock into a resting place when the printer is inactive. This resting place typically has a soft, foam-like pad that the print heads sit on. Ink tends to dry out here and in turn dries out the print heads. Tell your printer that you are going to change an ink cartridge so that the carriage comes away from it's resting place. Then locate the foam pad (you may have to use a flashlight, you will see the ink in it) and squirt a squirt or two of mild solvent like Mr. Clean in there. Re-dock the carriage and let it sit for five minutes, then execute a cleaning from your printer properties dialog. Do this a few times if necessary. In extremely dry climates, during off hours when the printer is not being used, print shops will do such things as moisten a paper towel with water and stuff it into the printer case near the print heads. A plastic baggie stuffed around it then creates a humid environment so the print heads don't dry out. This saves the waste of using ink in cleaning cycles.

What No Shmoobles said. Or if not a foam pad, it may be a rubber boot or seal. There is often a rubber or mylar wiper (think very small, very flexible squeegee) adjacent to the seal meant to wipe the print head clean. Both of these can get gummed up with ink. Also, as a good practice, when finished with the printer, properly power it down. A lot of users have those surge protectors with multiple power switches; killing the power to the printer in this way often does not properly "park" the print head, letting things dry out rather quickly. Make sure you're using the CL-41 cartridge, and you might want to check/clean the contacts in the carriage. On your print cartridge, you should notice some copper contact pads, and corresponding copper contact points on the printer's carriage where the print cartridge snaps in. Try cleaning both sets of contacts. Lastly, I've never been much impressed with aftermarket inkjet supplies, especially on pigmented inks. (Can't remember if the MP150 uses the Lucia inkset or what). Third-party inks tend to be very inconsistent, and I've seen some that are so bad, the pigments are not fully suspended in the ink and are mostly a layer of muck in the bottom of the ink cartridge. Poor quality inks will also gum up your cleaning station (where the wiper and the seal are) too, which can contaminate even a brand new OEM Canon cartridge.