Running an Antminer With a Hashboard Removed

Guide last verified: September 2026

Yes - an Antminer keeps hashing with one hashboard out for repair, on firmware that allows a partial set. Stock firmware stops the whole machine instead. Before you power it back up, close the empty slot. Air takes the easy path, and an open slot leaves the boards you kept with less air than they had when the set was full.

What the air does when a slot is empty

A miner is an air duct. The fan pushes air through parallel paths, one per hashboard, and the resistance in each path comes from the fins of that board's heatsink. Take a board out and you have not removed one third of the load from the cooling system — you have opened a path with almost no resistance at all.

Air divides between parallel paths in inverse proportion to their resistance, so the open slot takes a disproportionate share of everything the fan moves. This is the part that catches people out: the total volume through the machine goes up, and the amount reaching each remaining board goes down. It is not two thirds of the air for two thirds of the boards. It is worse than that.

What follows is ordinary. The boards you kept run hotter, the firmware answers by pushing the fans harder, and the machine spends the thermal headroom it used to hold in reserve. On a cool day you will never notice. In July it throttles, or it quietly ages chips until a second board is on its way to us.

Antminer S19j Pro+ stood on end with two hashboard slots empty and one board left in the middle, the fans visible straight through the open slots
Two open slots on a three-board machine, one board left in the middle. The whole cross-section of each empty path is clear of fins — you can see the fan straight through it.

If the board is still in your hands, leave it where it is

The advice you will find on the forums — do not pull the board out — is correct, and this page is not arguing with it. A board that has stopped hashing is still doing a job: its heatsink is still the resistance that keeps the air split the way the machine was designed to split it. A board reporting zero chips draws nothing worth reclaiming, so there is no power argument for removing it either.

So if the failed board is still in the machine, disconnect its data cable and its power, and leave it sitting in its slot. The duct is intact and there is nothing else to do.

That advice runs out the moment the board goes in a box. Nobody writes about what happens next, and that is what the rest of this page is for.

Closing the slot the board left behind

One rule matters more than any measurement:

Fill the full height of the slot, and run at least three quarters of the length the board used to occupy.

Get those two right and the geometry is right on any air-cooled machine, including one not listed below. Fall short on the height and you have left a bypass; fall short on the length and the air finds its way around.

Cut it from the packing foam the miner arrived in

Closed-cell polyethylene — the moulded insert that sits in every miner's shipping box. It is already the right material and the right size class, it costs nothing, and if the machine came to you boxed you already own it. Some people call the finished piece a baffle.

Moulded packing foam insert inside an Antminer shipping box with a tape measure laid across it
The moulded insert from the miner's own shipping box — this is the foam the block is cut from.

On the latest generation the box contains a single piece close to 12 3/4 x 9 x 2 inches, and it goes in as it is. On older nineteen-series boxes there is no single piece that size, so make the length up out of offcuts stacked end to end. There is no need to glue them: the airflow holds the stack together against the far end of the slot.

Two foam blocks cut from Antminer packing foam for an empty hashboard slot, a tape measure showing their length
Blocks cut for a nineteen-series slot. Where one offcut is not long enough, two are butted end to end — the top block here is made of two.

Sizes we cut, in inches, given as length along the airflow, then height, then thickness:

Machine Length Height Thickness
Nineteen series, L7, L9, Z15 Pro, and the altcoin machines 9 1/4 9 1/4 1 1/2
S21 Pro, S21 XP, S21+ 12 1/2 10 1 3/4
Z15 5 9 1/2 1 1/2

Between them these three cover every air-cooled Bitmain machine. Cut the thickness slightly generous rather than slightly shy — the foam compresses, and a piece that goes in with a little persuasion is a piece that is not going to shift.

The same Antminer S19j Pro+ with foam blocks fitted in both empty hashboard slots, the right-hand block made of offcuts stacked end to end
The same machine with both slots closed — full height, and most of the length the board used to occupy. The right-hand block is three offcuts stacked end to end; nothing glues them.

Nothing holds it in, and nothing needs to

The block is not fixed, clipped or taped. You slide it in and the airflow carries it to the far end of the slot, where it stops against the fan grille and stays there for as long as the machine is running.

That grille is the answer to the question everyone asks next. There is one behind the intake fans and another in front of the exhaust fans, and the fans themselves bolt to those grilles — a machine with its grilles cut out could not hold its fans in place at all. So the block has something solid to sit against, and the fan is on the other side of it. On the Z series there are no rear fans, and the grille is there regardless.

The one machine none of this describes is one that somebody has cut a grille out of. If that is yours, put the grille back before you put anything else in.

The cable and the power bars of the board you removed

Leave the data cable hanging where it is; there is nothing to do with it. The power bars stay in place too and are not in the way of anything. Taping is only needed in one situation, described next.

If you no longer have the box

Plenty of second-hand machines arrive without one. What matters is the shape, not the material: something that holds its form, fills the height, runs most of the length, and puts nothing conductive against the boards that are still working.

  • Kraft cardboard cut to size and taped or glued together. Everyone has a delivery box somewhere.
  • A piece of board or timber cut to the same dimensions.
  • Another dead hashboard of the right size — this is the one case where you do tape up: insulate it from the power bars, and leave its data connector unplugged.

Why nothing on your screen will look wrong

This is the reason the mistake survives so long. The miner keeps hashing. The boards you kept report exactly the hashrate you would expect from them. No counter turns red, nothing warns you, and the machine gives you no reason to go and look. Owners find out in a heatwave, or they never find out and a second board arrives at the lab six months later.

You do not need to open anything to check it for yourself. Note two numbers before you fit the block and the same two after the machine has settled: the chip temperatures on the boards that are still working, and the fan speed. Watch the fan speed as closely as the temperature — a machine holding the same temperature by spinning its fans harder has still spent the margin it used to have.

Antminer S19j Pro+ dashboard with the empty hashboard slots left open: board at 63 to 85 C, all four fans at 6000 RPM, 33.69 TH/s, 116 of 120 chips healthy
Slots open — the one board left reads 63 to 85 °C, all four fans at 6000 RPM at 100 % duty, 33.69 TH/s, and 4 of 120 chips already flagged.
Antminer S19j Pro+ dashboard with the empty hashboard slots closed with foam: board at 53 to 65 C, fans at 3270 to 3570 RPM, 40.75 TH/s, all 120 chips good
Same machine, same board, slots closed — 53 to 65 °C, fans at 3270 to 3570 RPM at 46 % duty, 40.75 TH/s, all 120 chips good. The only change is the foam.

The number on your screen is not the temperature of the metal

Worth knowing before any of those readings alarm you. The sensors sit on the hashboard, not on the heatsink, so what the interface reports is the board. The metal is considerably cooler. On our own bench, air entering at 25 C and leaving at 50 C goes with board sensors reading 70 to 75 C, while the heatsink itself rarely goes past 50 to 60 C.

That spread is also the answer to whether the foam minds sitting in there. It does not sit in room air — it runs the length of the slot and the side facing the boards comes up to heatsink temperature, which is the lower of those figures. The blocks we cut years ago are still in those machines and still the shape we cut them.

What not to do

  • Do not put anything conductive against the boards that are still working.
  • Do not restrict the intake or the exhaust. You are closing a path that no longer has a board in it, not narrowing the ones that do.
  • Do not remove a fan grille to make fitting easier. The grille is what the fan is mounted on and what the block rests against.
  • Do not expect a partial set to run on stock firmware. It will not; see below.
  • Do not pull boards out to make a machine quieter or cooler. It does the opposite — the boards left behind lose part of their air. Lower frequency and voltage is what brings heat and noise down.

Air-cooled machines only

Everything above applies to air-cooled miners. On hydro and immersion machines the boards sit in a sealed coolant loop, and taking one out opens that loop — a different job with different risks, and not one to improvise. Talk to us first if that is what you are dealing with.

None of this happens without firmware that allows a partial set

Stock firmware treats a chain that fails to report as a reason to stop the machine — not one board's share of the hashrate, all of it. That is why the question "can I run with two boards" has the answer "not as the machine ships". Firmware that lets you switch off the failed board and tell the miner how many chains are working is what turns a dead board into a temporary loss instead of a stopped machine.

The honest limit: a dead chip cannot be worked around. Only a whole board can be switched off, and that board still has to come to the lab. But it can travel while the rest of the machine keeps earning. Our firmware hub lists which models this covers and what it changes.

When the board does travel, our shipping guide covers packing it properly for the trip to our lab in the USA — and it is worth reading before you cut anything out of the packaging, so you keep what you need for the box and take the foam from what is left.

All repairs are performed personally by Aleksandr Muranov, with years of ASIC repair experience. See credentials →

Sent a board in and want the machine earning while it is with us? Contact our repair team and we will tell you what your model can run on.

Technical FAQ

Q: Can I run my Antminer with one hashboard removed?
A: Yes, on firmware that lets the miner run with fewer chains. Stock firmware treats a chain that does not report as a reason to stop the whole machine, so it will not mine at all. There is a second condition people miss: the slot the board came out of has to be closed off, or the boards that are left get less air than they had with a full set.
Q: Is it safe to run an Antminer with 2 hashboards instead of 3?
A: It is, for as long as the third board is away, provided the empty slot is blocked. The miner is an air duct. Air divides between the boards according to how much resistance each one puts up, and an empty slot puts up almost none, so it takes a disproportionate share of the flow. Close the gap and the air goes back to the boards that need it.
Q: Should I remove the dead hashboard or leave it in the miner?
A: If the board is staying with you, leave it in the slot and disconnect its data cable and power. The duct stays intact and there is nothing else to do. You only need to close the slot once the board physically leaves the machine, which in practice means the day you ship it for repair.
Q: Is the dead hashboard still drawing power?
A: A board reporting zero chips is not consuming anything worth removing it for. Pulling it out to save power is not a reason. Pulling it out to send it for repair is.
Q: What happens if I just leave the hashboard slot open?
A: The machine keeps hashing and the dashboard looks normal, which is exactly why this gets missed. The remaining boards run hotter than they did before, the firmware answers by pushing the fans harder, and the machine spends the thermal headroom it used to have. On a cool day nothing happens. In July it throttles, or it quietly ages chips until a second board comes back to us.
Q: What can I use to block off an empty hashboard slot?
A: The packing foam the miner shipped in. On the latest generation there is a single piece in the box that is already close to the size you need; on older boxes you make it up out of the offcuts, stacked end to end along the slot — there is no need to glue anything. Two things decide whether it works: it has to fill the full height of the slot, and it has to run at least three quarters of the length the board used to occupy.
Q: How do I know blocking the slot actually did anything?
A: Read your own dashboard. Note the chip temperatures on the remaining boards and the fan speed with the slot open, fit the foam, and read the same two numbers again once the machine has settled. You do not have to open anything or measure anything to see the difference. Watch the fan speed as closely as the temperature — a machine that holds the same temperature by spinning its fans harder has still lost the headroom it had.
Q: The temperature my miner reports looks high. Is that the temperature of the metal?
A: No, and this is worth knowing before you panic about any number on that screen. The sensors sit on the board, not on the heatsink, so the figure you read is the board, and the metal is a good deal cooler. On our own bench, air going in at 25 C and coming out at 50 C goes with board sensors reading 70 to 75 C, and the heatsink itself rarely goes past 50 to 60 C.
Q: Can I pull a hashboard out to make the miner run cooler or quieter?
A: No, and it does the opposite of what you want. The boards you leave in get less air than they had before, not more, so they run hotter. What actually brings the heat and the noise down is running the machine at a lower frequency and voltage, which is a firmware job, not a screwdriver job. Take a board out when it is going away for repair, not to cool the machine down.
Q: Will the foam get pulled into the fan?
A: It cannot reach the fan. There is a grille behind the intake fans and another in front of the exhaust fans, and the fans themselves bolt to those grilles — a machine missing them could not hold its fans in place. Airflow pushes the foam block up against that grille and it stays there. The one machine this does not describe is one somebody has cut the grille out of.
Q: What do I do with the ribbon cable and the power bars of the board I took out?
A: Leave the ribbon cable hanging where it is; there is nothing to do with it. The power bars stay in place too and are not in the way. The only time you need to tape anything off is when you fill the slot with another board instead of foam.
Q: Does the foam not overheat sitting in there?
A: It gets warm, and the numbers are measured rather than assumed. The foam block runs the length of the slot, so it is not sitting in room air: the side facing the boards comes up to heatsink temperature. On our own bench, air entering at 25 C and leaving at 50 C goes with board sensors reading 70 to 75 C, while the heatsink the foam block is actually next to rarely goes past 50 to 60 C. The blocks we cut years ago are still in those machines and still the shape we cut them.
Q: I do not have the box the miner came in. What else can I use?
A: Kraft cardboard cut to size and taped together works, and everybody has a delivery box. So does a piece of wood, or another dead hashboard of the right size — tape it clear of the power bars and leave its data connector unplugged. The material matters less than the shape: full slot height, at least three quarters of the board length, nothing conductive touching the boards that are still working.
Q: Does it matter which slot is empty, or how many?
A: No. Edge slot or middle slot behaves the same. If two boards are out, you can put the one you have left at the edge and fill the other two slots, or put it in the middle and fill both sides — it makes no difference to the air.
Q: Does this apply to hydro or immersion miners?
A: No. Those boards sit in a sealed coolant loop and taking one out opens the loop, which is a different job with different risks. Contact us before you take anything apart on a hydro or immersion machine.
Q: My board is at your lab. Do I have to leave the miner switched off until it comes back?
A: No, and that is the point of this page. On the models our firmware supports you switch off the failed board, close the slot it left behind, and the machine keeps hashing on what is left. A dead chip cannot be bypassed, so the board itself still has to come in.