Help with printer

My printer has started to print some pages out in a red colour instead of in black ink. On other pages it's totally fine and black ink comes out. This signals to me that I should probably change a cartridge, but which one? The coloured or the black one? Sorry if this question appears dumb
I can't ask at work as I'm the 'techiest geek' here

Does your printer have a test page function? If you print that it should indicate which cartridge is deficient.

Probably the black one, but if its printing red instead of black it sounds like it might be making black by mixing colors anyway, which means your black might be full and the color one might be empty. Isnt there an indicator level display? Or the option to print out a status page with the fullness of the cartridges on it? What model is it?

HP 5550. How do I do a test print?

Assuming you mean deskjet rather than laserjet there should be an on screen level indicator. You should be able to google for the instructions to print a test page or find it in the menu. I had a quick google and only found unqualified suggestions.

This may give you some indication.

I'd suggest you need cyan ink if it is printing black reddish.

To do a test page from windows, go start/settings/printers & faxes. Double click on the icon for your printer, and then select printer/properties

There should be a button to click marked 'Print Test Page'.

The windows test page wont tell you how full or empty your cartridges are though. But if you installed a utility program with the printer, that probably will.

take both cartridges out and shake em (the cartridges!) if one's still got ink in you'll hear.
to do a test print hold down the on/off button and the 'paper' button at the same time.

UA, HP 5550, lift lid, where HP logo is situated, press top button on right hand side, cartridges will move to left, you will see some pictures there, to the left of the pictures there is a small relief showing 2 dots, whichever cartridge is under the 2 dots needs replacing,
reason I know is I have the same printer on my desk (owned by the same company)if you follow my drift,

Hmm not always though, my ones at home have the ink soaked in something like cotton wool or tissue paper inside the cartridge, and dont make any noise when shaken.

works with my HP though! grr UA you have a better printer than me what that all aboutlike?

Just switch them with your neighbors when they are getting coffee

Just buy a new printer

Ok none of the above options worked, so I called the internal helpdesk. She didn't know how to print a test page either (!) and she told me to print out different coloured letters from word to check them. They passed, and the plain black text passed too - all was fine. Her next suggestion was to try taking the colourd ink out and see how it printed. 5 minutes for this 'vauable' advice from her which didn't work!

@Moonboot - tried that too but it just printed an HP welcome page, no test page.

Not too far from the truth. They undersell the printers, because they know that the money is in the ink. Black gold.

Moonboot - we got these about 1-5 yrs ago too along with our huge flatscreens

@BrokenM haha maybe if it's not solved by hometime

just change BOTH cartridges we recycle them anyway!
oy missus I was one of the first to get the Flatscreens too! cheeky chops!

@Jellyone I have no dots or HP logo there.
Edit: I was trying to save money, Moonboot

Aha, I just printed a test page and it looks like the coloured ink. The guy who helped me used Serenissima's method - I just did it wrong before when trying.

Thanks for everyone's help!