Hydro-cooled ASIC miners — the S19 XP Hydro (BM1366), S19 Pro+ Hydro, S21 Hydro and T21 Hydro (BM1368) — live or die by their sealed coolant loop. Daily maintenance comes down to four things: keep the loop sealed and leak-free, keep the right coolant in it, never let that coolant freeze, and never let liquid meet an energized hashboard. Get those right and a hydro machine runs quieter, cooler and denser than any air-cooled equivalent. Get them wrong — especially the freeze rule — and you crack a plate or connector that is expensive or impossible to repair.
How a hydro miner moves heat
Unlike an air-cooled unit that blows air across finned heatsinks, a hydro miner clamps a water block (cold plate) directly over the ASICs on each hashboard. Coolant is pushed through those plates by an external Coolant Distribution Unit (CDU), which carries the absorbed heat to a dry cooler or heat-reuse loop. The entire wetted path — plates, hoses, quick-disconnect fittings and the CDU — is one pressurized, sealed circuit. Everything below is about protecting that circuit and the electronics it sits against.
Daily checks (five minutes per unit)
- Walk the loop for leaks. Look and feel around every fitting, quick-disconnect, hose barb and the brazed edges of each hydro plate. Any bead of moisture, crust, or discoloration on the brazing is an early warning — treat it as a fault, not cosmetic.
- Read coolant temperatures in firmware. The dashboard reports inlet/outlet or board temperatures. A rising delta or a board climbing toward its thermal cutoff usually means restricted flow, air in the loop, or a fouled dry cooler — not a dead chip.
- Confirm flow and pressure. Verify the pump is running and loop pressure sits in the CDU’s normal band. Loss of flow strands heat on the plates in seconds.
- Check the CDU reservoir level. A slowly dropping level points to a weeping fitting or micro-leak somewhere upstream.
- Listen and feel. Gurgling means trapped air; hot spots on an otherwise cool plate mean a channel is starved.
Use the right coolant — never pure or tap water in freeze-risk areas
The single most damaging mistake with hydro machines is filling the loop with pure or tap water in a climate that can freeze. Follow the manufacturer’s coolant specification: in any location with a real risk of sub-zero temperatures, use the specified anti-icing (glycol-based antifreeze) coolant, not plain water. A proper coolant does three jobs at once — it lowers the freeze point, carries corrosion inhibitor to protect the plates and fittings, and resists the scale and biological growth that plain tap water leaves behind. Tap water additionally introduces minerals that foul the narrow channels inside the cold plates. Always mix and top up with the fluid the manufacturer lists; do not guess a ratio.
The freeze failure mode (a real field case)
A returned unit showed three linked failures: leakage on the hydro plate, bulging and splitting at the brazed seams, and a cracked coolant connector. The root cause was thermal shock plus trapped water. The operator ran a room at roughly 23°C while the outdoor environment sat near -17°C, disassembled the machine, and did not drain or dry the coolant path before moving it. Residual water inside the plate froze, expanded, and forced the brazed seams and the connector apart. Water is nearly incompressible and gains volume as it freezes — a plate that is fine at operating temperature can be destroyed overnight once it is powered down in the cold with liquid still inside.
Draining before storage, transport or RMA
Any time a hydro machine will be powered off in a cold environment, shipped, or set aside for storage, purge the loop first:
- Disconnect the unit from the CDU at the quick-disconnects and let the plates drain.
- Blow the residual liquid out of the hydro plates with a low-pressure air pump until no more coolant comes through. This is the step the field-case operator skipped.
- Plug the water inlet and outlet with the supplied caps before boxing the unit. This keeps the remaining film sealed in and stops coolant from weeping into the packaging.
- Label the box so whoever opens it knows the loop was drained.
A plate with even a small trapped pocket of water can crack in transit through a cold warehouse or truck. Purge and plug, every time.
Electrical safety around a wet machine
Two rules keep hydro maintenance from becoming dangerous. First, never let coolant reach an energized or exposed hashboard. If liquid flows onto a powered board it can short and burn traces, and a scorched hashboard is often beyond economical repair. Kill power at the PSU before you open, drain, or reseat any wetted component, and dry the area before re-energizing. Second, know where the real shock hazard lives: the low-voltage DC bus feeding the boards (single-digit to low-double-digit volts) is not a shock risk, but the miner’s power supply holds mains-voltage capacitors charged to roughly 400V+ even after unplugging. Leave the PSU sealed and let it bleed down before working near it. Coolant work and PSU internals do not mix.
What voids the warranty — and when to escalate
Freeze damage, leaks from an improperly sealed or refilled loop, and coolant contact with the electronics can all void your coverage, so document your maintenance and stop before you make a failure worse. If you find bulging brazing, a cracked plate or connector, coolant that has reached a hashboard, or a leak you cannot trace and seal, take the unit offline and get it on a bench rather than running it wet. A machine that has lost its pool or network connection is not the emergency here — firmware simply idles it — but a leaking or frozen loop is.
Related: Diagnose a suspected board or thermal fault with the ASIC fault finder, review the manufacturer’s coolant and handling specs in our miner manuals library, learn the loop hardware in the Coolant Distribution Unit (CDU) glossary entry, or send a leaking or freeze-damaged unit to us via start a repair.
