Almost every “my pen is broken” email we get turns out to be one of five things. Here’s how to tell which one you’re dealing with, and what the major pen makers say to do about it.
The dial won’t turn, or stops at a number
Likely cause: the cartridge is running low.
Many pens stop the dial at the amount left in the cartridge. Novo Nordisk’s NovoPen Echo Plus manual says it directly: when the cartridge is low, “the dose counter stops at the number of units left.” Other pens let you dial past it and then stop partway through the press.
Fix: check how much is left in the cartridge. If it’s nearly empty, load a fresh one. Don’t force the dial. The same manual says, “Do not force it to turn.”
The button won’t press, or stops early
Likely cause: a blocked or missing needle.
This is the most common one. Lilly’s HumaPen Luxura manual: “If the injection button is hard to push, the needle may be clogged. Attach a new needle.” Novo’s manual says the same thing if the button stops before the counter reaches zero.
Fix:
- Make sure a needle is on and screwed all the way.
- Replace it with a new one. Reused needles clog far more often.
- Press slowly. Thicker solutions need more time, especially through a 32G needle. See pen needles explained.
Never dial and press with no cartridge in the pen. Owen Mumford’s Autopen instructions specifically warn against it.
The plunger rod is sticking out after a cartridge change
Likely cause: the rod moved forward with the last cartridge and needs to go back.
When a cartridge is used up, the plunger rod (also called the piston rod or lead screw) is extended. Before the new cartridge goes in, it needs to be back at the start. Novo’s manuals: “If the piston rod sticks out, push in until it stops.” Lilly’s: “use the cartridge plunger to push the screw back.”
Fix: with the cartridge holder off, gently push the rod back in until it stops. Then load the new cartridge. If it won’t go back with gentle pressure, stop and email us. Owen Mumford warns that resetting the rod incorrectly can damage a pen, so don’t force it.
The pen drips after you stop pressing
Likely cause: air in the cartridge.
Lilly’s HumaPen manual says air in the cartridge makes the pen sputter or drip until it’s all purged. Air compresses, then keeps pushing after you let go.
Fix: purge it. Put on a needle, dial 0.10 to 0.20 mL, point the pen up and press until you see a clean drop. Our fill guide covers it step by step.
Leaking from the back of the cartridge is a different problem. That’s almost always a plunger pushed out during filling. See the fill guide’s vent needle step.
The cartridge holder won’t screw on
Likely cause: the cartridge isn’t fully seated, or the threads are crossed.
Lilly’s manual starts with the basics: make sure the cartridge is fully inserted into the holder. Then line the holder up straight with the pen body before turning. If it binds after a turn or two, back it off and start again. Forcing it can strip the threads.
On the V2 and V3, if you can’t find the holder at all, it’s under the front metal cover. See where to find the cartridge holder.
Care habits that prevent most of this
Pulled from the NovoPen, HumaPen and Autopen manuals, which agree on almost everything:
- Take the needle off after every use. Leaving it on lets air in, lets liquid out and clogs the needle.
- Wipe, don’t wash. A damp cloth with mild soap. Don’t soak, submerge or oil the pen.
- Skip harsh cleaners. Novo and Lilly both say no bleach or alcohol on the pen body or dose window.
- Don’t drop it. If you do, check the cartridge for cracks before using it again.
- Store it capped, needle off, in a case.
Still stuck? Every PepPen has a 6-month warranty. Email support@thepeppen.com and we’ll sort it out within one business day.
All PepPens products are sold for research use only.
