From GT New Horizons
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A Multiblock is a machine built from more than one block. This can be as little as two for the smallest of the Railcraft Boilers, or hundreds of blocks for end game superstructures. Multiblocks almost always use more than one type of block in their construction, though there are a few exceptions such as the Water Tank. Builds have a set of design limitations; a specific size and placement in order to be a valid structure. Some are flexible or can be configured in multiple variations, while others can only be put together one way. One of the unique features of GT multiblocks is that they can Wallshare with other multis, both making use of the same blocks in their structure.


New Horizons makes heavy use of multiblock structures and has sets of tiered blocks that are common to many such machines.


GUI for the Electric Blast Furnace. The top half is a black screen with words "Running perfectly". In the middle are four buttons on the left, void mode, input separation, batch mode and lock recipe. The bottom right corner has a green power button and an empty slot.
Multiblock GUI (2.3.0+)

A Controller is the heart of a multiblock. It defines what the structure tries to form as. Controllers are named according to whatever machine they form, such as Pyrolyse Oven or Electric Air Filter (T1). Holding left-Shift while hovering over a controller in NEI or the inventory will show a list of blocks the controller expects in order to form a valid structure.[1]

Hit a controller with a Soft Mallet to turn the machine on and off. As of 2.3.0, the power button in the lower right of a controller's GUI can also toggle the multiblock on/off. Below the power button is a storage slot used in some multiblocks like the Air Filter for a consumable or swappable part. The four buttons in the middle are Void Mode, Input Separation, Batch Mode and Lock Recipe.

Some simple multiblocks do not have controllers, such as the Water Tank, Coke Oven and Railcraft Boilers.


Casing blocks fill in any spaces not occupied by the controller, hatches, busses and other specific function blocks. Some multis have their own dedicated casing block type, but most are shared between several multiblock builds. For example, Frost Proof Machine Casings are used in the Vacuum Freezer, Hydro Pump, Hydro Turbine, and Mega Vacuum Freezer. Casings have no special function outside of filling in a structure or gating the overall efficiency/capacity of a multiblock.

Heating Coils

Coils are used in a few multiblocks that use electricity to heat up. Upgrading coils allows the associated multilblock structure to be more efficient and/or access to higher tier recipes.

Input Bus

An Input Bus is for supplying solid items and setting a control circuit or ghost circuit. Fluids and gasses cannot be supplied via cells/buckets/containers in the Input Bus; these ingredients need to go in the Input Hatch. Tier of the bus determines its slot capacity, from four at LV up to sixteen at HV and beyond. Sneak-right-clicking with a Screwdriver toggles sort mode on/off.

Input Hatch

Liquids and gasses must go into the Input Hatch's tank. The Input Hatch can hold a reserve of fluid cells and will automatically empty them as it drains, capacity permitting. It cannot empty cells that have more fluid in them than it can hold at once. Fluid Pipes, Fluid Conduits or any other fluid delivery system can also be used to automatically stock an Input Hatch.

Output Bus

The Output Bus is where finished items will be deposited after processing. If a valid inventory is placed adjacent to the Output Bus's output face (dark grey square with orange triangles), it will automatically push items into the inventory, no Conveyor needed. Otherwise items will accumulate in the Output Bus until emptied. A ULV Output Bus is passive, and will not auto-output. If the Output Bus is full, the machine will stop processing if Voiding Mode: Void Nothing is active (default). The Voiding Mode can be changed to Items, Fluids, or Items & Fluids, which will cause the Multiblock to continue to process even if its output(s) are full, destroying any excess outputs in the process.

Output Hatch

An Output Hatch is the destination of any fluid or gas produced by a multiblock. Right-clicking / Shift-right-clicking with a Screwdriver cycles through various restricted options, limiting what can go into an Output hatch; this is useful when multiple hatches are on the same multiblock for automated routing. Total capacity of the Output Hatch is based on its tier. Alone, this block can serve as a tank or empty/fill other containers.

Muffler Hatch

The Muffler Hatch gives a bonus reduction to pollution output and determines the percentage of waste gas recovered for some recipes. By default an LV Muffler Hatch has no reduction or gas recovery, but is still required to successfully form the multiblock. A Portable Scanner will show the current pollution reduction afforded by the Muffler, or look at the tooltip in NEI.

Maintenance Hatch

The Maintenance Hatch is where any Maintenance issues need to be addressed. There are no tiered block sets the Maintenance Hatch, though it has several upgrades.

Energy Hatch

Energy Hatches determine what recipes a multiblock can perform, how much power it can accept, and if it will overclock or not. Each hatch accepts up to 2A of its tier. The number of Energy Hatches in a Multiblock generally determines its tier of operation; two hatches will make the multiblock attempt to run its recipes at Energy Hatch+1 tier. This may cause a power failure if one or both hatches don't get enough EU to satisfy the increased demand.


If a multiblock isn't working, the first thing to do is look at its controller. If it says HAS PROBLEMS, the multi requires Maintenance. Newly built multiblocks always require a full set of maintenance repairs. If the controller says INCOMPLETE STRUCTURE, it's missing one or more parts, parts are in the wrong place, and/or there are too many or not enough of a part to be a valid structure. The controller can take several seconds to update its status, so be patient after changing part of a multiblock. If all else fails, sometimes it's easiest to completely disassemble a multi and start again, verifying each block placed.

Diagnosing Problems
  • Needs Maintenance
    • Use tools inside Maintenance Hatch GUI
  • Right-click with Tool Box on Maintenance Hatch
    • Must have full complement of tools
    • Soldering Iron must be charged
    • Needs soldering material (consumable)
  • Volcanus with no Pyrotheum
    • Causes voiding & maintenance issues
  • Cryogenic Freezer with no Cryotheum
    • Causes voiding & maintenance issues
  • Multiblock built incorrectly
    • Missing parts - left-Shift over controller in NEI[1]
    • Parts are in the wrong position
    • Exceeds maximums or does not meet minimums
    • Wrong casings - Some blocks are visually similar
    • Energy Hatch is insufficient tier
    • Mixed coils or casing types
    • Controller is facing the interior of the multiblock
    • Something inside a multi that should be hollow
  • Structure not recognized
    • Not built in one chunk or fully chunkloaded
    • Break and replace Controller
Won't Turn On Turns On then Voids / Shuts Down
  • No power
    • Power line has breaks / not connected
    • A cover is blocking power transmission somewhere
    • Transformers are not oriented properly
    • Energy Hatch input (╬) isn't facing power
    • Generator(s) aren't turned on and connected
    • Generators(s) out of fuel
    • Battery Buffer has no batteries
    • Batteries are not charged
    • Battery and Buffer tier don't match
  • Incorrect recipe
    • Liquids aren't in Input Hatch
    • Items aren't in Input Bus
    • Circuit not set in Input Bus / Controller
    • Wrong ingredients, verify by metadata
    • Coils/Casings/Energy Hatch insufficient tier for recipe
    • Blocked by unusable recipe items in busses/hatches
  • Disabled
    • Hit with Soft Mallet
    • Press power button in controller
  • No Energy Hatch
    • Add at least one Energy Hatch to accept power
  • Structure insufficient
    • Multiblock configuration doesn't meet recipe's needs
    • Gas/liquid needs an output in a different location
  • Insufficient power
    • Not enough power generation - check recipe
    • Too much power being used by other machines
    • Not enough power delivered due to cable loss
    • Over-limited by diode or transformer
    • Battery Buffers only output 1A per battery
    • Recipe is overclocking, consuming more power than expected
    • Not all Energy Hatches are connected to power
    • Not enough Energy Hatches to accept power (2A max each)
  • Muffler Hatch blocked
    • Muffler is not pointing out
    • Muffler does not have an air block above it
    • Advanced Muffler Hatches need air filters
  • Missing Consumables
    • Turbine item for Air Filters and Turbines
    • Cryotheum for Cryogenic Freezer
    • Pyrotheum for Volcanus
Wrong Output Voids at Random / Runs Intermittently
  • Incorrect circuit set
  • Input separation not enabled on a multi-bus setup
  • Water/Lava conditions not met for Rock Breaker
  • Power loss
    • Another machine is competing for amps
    • Power production is inconsistent
  • Job Done
    • No ingredients left to process
    • No pollution in chunks for Air Filter
"Needs more power" "<X> overflowed"
  • Insufficient Energy Hatch tier
  • Insufficient casing/hull tier for recipe
  • Coil / heat casings mismatch
"Not enough output space" "No valid recipe found"
  • Output doesn't have enough slots for the recipe.
  • Output is full/missing
  • Missing an output for directional products
    • EBF needs one on top for gas, one bottom for items
  • No combination of valid items / wrong item
  • Missing input hatch/bus
  1. 1.0 1.1 While controller tooltips are almost always reliable, sometimes bugs do slip in. This Github issue lists most mistakes.


  • A full Output Bus will not void any extra items produced unless the Voiding Mode of the Controller is changed.
  • Insufficient energy supply will destroy the currently processed material.
  • Do not allow a multiblock to be only partially chunk loaded. Doing so can lead to unpredictable behavior.
  • Before using a multiblock for the first time, Maintenance must be performed.
  • To activate or deactivate a multiblock, hit its control block with a Soft Mallet, or press the Power button in the Controller GUI.
  • Filled large fluid cells (search for large*cell in NEI) can be used in the Input Hatches as buffers.
  • To reduce Pollution production, keep mufflers upgraded to the highest tier available.
  • Busses and Hatches are redstone transparent, they cannot pass redstone signals.