Espresso Machine Produces Excessive Pressure
Excessive brewing pressure is the mirror of the low-pressure fault, and its causes obey the same physics from the opposite direction. Pressure builds when water meets resistance; when the resistance is too great, the machine operates above its intended range, shots choke and run in slow drips, and the safety systems of a healthy machine may begin to intervene. As with low pressure, the fault divides between the coffee preparation and the machine itself, and the preparation is again the more common source.
A grind that is too fine is the dominant cause. Espresso demands a fine grind, but fine has a ceiling: beyond it, the packed particles become nearly impermeable, water cannot pass at the machine's normal flow, and the pressure climbs while the shot barely emerges. The classic symptom is a choked extraction, drops rather than a stream, taking far beyond the usual time and tasting harsh and bitter. A one-step coarsening of the grinder usually transforms the shot.
An excessive dose and over-tamping complete the preparation causes. A basket loaded beyond its capacity leaves too little headroom and packs the water path too densely, and a tamp pressed with excessive force adds its resistance, though, as with low pressure, the machine's own pressure largely compresses the puck and moderates tamp differences. When dose and grind are both at their limits, the combined resistance exceeds what the machine was designed to brew against.
On the machine side, blockages produce genuine excessive pressure. A blocked filter basket, its holes clogged with fines and oils after many uncleaned shots, resists water exactly as an over-fine grind does. A blocked group head, where the dispersion screen and its passages are scaled or caked with coffee residue, restricts the water before it even reaches the puck. Both are corrected by cleaning: soaking the basket, scrubbing or replacing the screen, and backflushing the group with an approved detergent.
A pressure-valve problem is the most serious machine cause. Espresso machines regulate their maximum pressure with an over-pressure valve, and a valve that is jammed, scaled or misadjusted permits the pump's full output into the group. Machines with gauges display this directly, with the needle climbing past the usual range; machines without gauges betray it through chronically choked shots despite a verified, normal preparation. The expansion valve on heat-exchanger machines serves the same protective role for boiler pressure, and its failure can cause both excessive brewing pressure and related symptoms such as dripping from the relief path. Valve servicing is a technician's task, since it involves pressurised components and precise adjustment.
Distinguishing preparation from machine follows the same blank-basket logic as the low-pressure fault, reversed. If, against a blank basket, the machine reaches only its normal range, the hydraulics are sound and the resistance of the puck is the culprit, coarsen the grind, reduce the dose or ease the tamp. If the machine overshoots its normal range even with a blank basket or with no coffee at all, a valve or adjustment fault is confirmed and professional service is warranted.
Prevention includes keeping the grinder adjusted rather than drifting ever finer, replacing and cleaning the group screen as routine maintenance, backflushing on schedule, and descaling in hard-water areas so that valves and passages remain free.
Excessive pressure should not simply be worked around. A machine habitually brewing above its intended range stresses its pump, seals and boiler fittings, and if the over-pressure protection is itself the failed part, the machine is operating without its intended margin of safety. Persistent symptoms despite a correct preparation deserve inspection rather than a coarser grind as a permanent accommodation.
