Guide · printer fix

Printer prints blank

The printer is working — the paper is the wrong way up. Thermal paper takes heat on one side only, so a roll loaded coated-side out gives you a perfectly clean slip every time. Scratch the paper with a fingernail: the side that leaves a dark mark must face the print head.

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Whatever the printer does, the sale is already saved — the register writes the bill to its own database first and queues the paper second. The full nine-symptom checklist covers the rest.

Most likely cause

The roll is in coated-side out — that is nearly always all this is.

The roll is upside down. Thermal paper has a heat-sensitive coating on one face and nothing on the other. Load it with the plain face against the print head and the printer works exactly as designed and produces nothing.
It usually happens on a reload, mid-rush. Nobody loads a roll backwards at leisure. If blank slips started the moment someone changed the paper, you have your answer without testing anything.
Occasionally the paper is simply finished. A roll that has sat in a hot kitchen for months goes faint, then blank. That one shows up as faint print first, so if the last few slips were pale, suspect the paper rather than the loading.

The fix

Do this first.

Scratch the paper with a fingernail or a coin

Drag something hard across the paper firmly. A dark line appears on the printable side. If neither side marks, the paper is dead rather than backwards — open a fresh roll and start again.

Reload the roll with the marked side facing the print head

On most counter-top thermal printers the paper feeds off the underside of the roll, not over the top — so flipping the roll over in the well is usually the whole fix. Close the cover until it clicks; most printers refuse to print with the lid a millimetre open, and say nothing about it.

Run a test print from Settings → Printers & KDS

Each printer's row has a Test print key. The slip prints the words Test print, the paper width it thinks it has — 80mm · 42 columns, or 58mm · 32 — and a row of digits as a width ruler. If the ruler runs off the edge of the paper, the width setting on that row is wrong and worth fixing while you are here.

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On the register

What the printer's row says.

Every printer you have added has a row in Settings → Printers & KDS, and the row carries its own status in words rather than a green dot. These are the exact words for this one.

While it is wrong: Connected. The register cannot see this one, and does not pretend to — a printer that accepts a job and heats a blank strip has done everything it was asked.
Once it is fixed: Connected, unchanged. The proof is the slip in your hand, not the screen.

The register does read the printer's paper sensor, so a roll that has actually run out shows as “Paper out” with printing paused and tickets held in the queue. There is no ESC/POS status for “the roll is in backwards”, so no honest register can show one.

The Counter Printer row in Settings → Printers & KDS reading Connected, with Check printer, Test print, Test connection, Edit and Remove beneath it.

The row reads Connected before, during and after a blank slip — the register has no way to see paper loaded backwards, so the words on the row never change.

Nothing is lost

Printing what was missed.

Nothing failed, so nothing is waiting. As far as the printer was concerned the job printed, so it is marked done and the print queue is empty. You are reprinting by choice, not recovering.
The last bill and the last KOT are one key each. Settings → Printers & KDS has Reprint last receipt and Reprint last KOT under Reliability. That covers the slip that just came out blank.
An older bill comes back from Orders. Open the order and press Reprint receipt. The copy keeps the original invoice number and date and carries a DUPLICATE stamp, so two slips can never be read as two sales.

Straight answers

Printer prints blank — the questions that follow.

The roll is the right way round and it is still blank — now what?

Two things are left. One: the paper itself is dead — thermal rolls fade with heat and sunlight, and a roll stored above a tandoor is finished inside a month; try a fresh one. Two: the print head is dirty — switch the printer off, open the cover, wipe the head with cotton and a little isopropyl alcohol, let it dry. Still blank after both? Run the printer's own self-test: hold its feed button while switching it on. If that slip is blank too, the fault is in the printer, not in EasyKOT.

Which way does the paper go in a thermal printer?

Printable side against the print head. On almost every counter-top receipt printer that means the paper comes off the underside of the roll and out towards you — if you are feeding it over the top of the roll, flip the roll. The scratch test settles it in two seconds: whichever face takes a dark line is the face that must touch the head.

Does a blank slip mean I lost the bill?

No. EasyKOT writes the sale to the register's own database before it queues any paper, so nothing about printing can cost you a sale. Reload the roll and reprint whenever you like — the bill has been safe the whole time.

Can EasyKOT warn me before the roll runs out?

On a printer that answers status questions, yes — the row reads “Paper running low” while the near-end sensor is tripped, and “Paper out” when it is finished. Plenty of budget printers never answer at all; those read “Can't verify — will still try to print”, which is the honest answer rather than a false green.

Every printer guide is listed on the guides hub.

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