Strada AV’s heat-up expansion ceiling is printed as 13 bar and as 11–12 bar

La Marzocco’s commercial operating manuals tell installers what to do when the coffee-boiler pressure reading climbs during heat-up. On the Strada AV manual, that instruction does not settle on one number. The heat-up procedure says keep the reading from exceeding 13 bar. A later Note on the same expansion-(safety)-valve check says keep it from exceeding 11–12 bar, and treats a reading above 12 bar as the trigger to adjust the valve. Linea PB manuals print 11–12 bar in both places.

What follows is a manufacturer diagnostic acceptance criterion that disagrees with itself inside one document, set beside two Linea PB manuals that do not carry the same internal split. It is not a service procedure, not a ranking of Strada against Linea PB, and not a claim about what brew pressure should read during a shot.

What the heat-up check is measuring

In all three manuals, the relevant step sits under waiting for the machine to heat after installation fill. The coffee-boiler heating element is on; water expands; the coffee-boiler pressure indicator may climb as high as 14–15 bar. The manuals treat that climb as a reason to set the expansion (safety) valve so the heat-up reading stays under a stated ceiling.

The measurand is therefore idle heat-up coffee-boiler pressure under thermal expansion, with the heating element energised. It is not a portafilter-out flow-rate test, and it is not the pump-bypass brew-pressure setting used later when a group is brewing.

The Strada AV split

Source document: La Marzocco Strada AV Operating Manual V2.0 — 12/2016, document code MAN.16.1.02EN on the title page.

In section 2) Waiting for the Espresso Machine to Heat to Operating Temperature, the procedure says the coffee-boiler pressure pointer may reach 14–15 bar whenever the heating element is on, and that in that case the expansion valve must be adjusted so that pressure never exceeds 13 bar.

On the next page, under the water-pump section, a Note restates the same physical situation — heating element on, water expanding, expansion (safety) valve discharging drops — and says the valve should prevent pressure from exceeding 11–12 bar. It then says that if pressure exceeds 12 bar, the expansion valve must be adjusted. The same Note also maps a valve stuck open in the drain position to an inability of pressure to increase to about 8 bar.

Those are not the same acceptance line:

The parts description’s 13 bar spring figure matches the procedure’s ceiling and does not match the Note’s 11–12 / 12 band. The file does not say which line supersedes the other, and it does not mark either passage as obsolete.

This article reports the conflict. It does not reproduce the Note’s adjustment steps as instructions.

Linea PB does not carry that internal split

Two Linea PB operating manuals were checked for the same heat-up / Note pair:

In both, the heat-up procedure says adjust the expansion valve so pressure may never exceed 11–12 bar. In both, the later expansion-(safety)-valve Note says prevent pressure from exceeding 11–12 bar and treats a reading above 12 bar as the adjustment trigger. The stuck-open / about 8 bar clause appears in both Notes as well.

So the 11–12 / above 12 wording is stable across these two Linea PB revisions nearly nine years apart. What the Strada AV file uniquely shows among these three manuals is the 13 bar heat-up procedure line living beside that same 11–12 Note.

The Linea PB coffee-boiler parts sections state a factory hydraulic test at 18 bar and an operating pressure of 9 bar. They do not, in the passages relied on here, reprint Strada’s “spring adjusted to 13 bar” coffee-boiler safety-device sentence. That absence is scoped to those Linea PB pages; it is not a claim that Linea PB hardware lacks an expansion valve.

The same gauge, a different role

The conflict above is about heat-up expansion pressure. The manuals also attach a brewing claim to coffee-boiler pressure hardware:

• Linea PB V3.2 and V5.1, immediately after the heat-up 11–12 bar line, state that in normal operating conditions the coffee-boiler pressure gauge can read 0–12 bar, and that when brewing, the pressure should be set to 9 bar.
• Strada AV’s heat-up page says that in normal operating conditions the coffee-boiler pressure transducer, while brewing, can read anywhere from 0–12 bar. Separately, its coffee-boiler parts description gives an operating pressure of 9 bar.

Those brewing figures are not the heat-up expansion ceiling. A high reading while the heater is raising a closed boiler is the expansion-valve check. A 9 bar brewing setpoint is a pump / brew-path claim made under different conditions. Collapsing them into one “coffee boiler pressure should be X” diagnosis is not what these manuals support.

A related naming note appears on the Linea PB fill sequence: air trapped while the steam boiler fills can register on the steam pressure gauge as “false” pressure that must be bled by opening the steam valves. That sentence is manufacturer language for a gauge reading that is not steam operating pressure. It is cited here only as a named example of the same instrument class reporting a different physical cause; it is not used to decide the Strada 13 versus 11–12 question.

Scope and limits

On Strada AV MAN.16.1.02 EN V2.0 (12/2016), the heat-up expansion-valve check is printed once as never exceed 13 bar and once as prevent exceeding 11–12 bar / adjust above 12 bar, while the coffee-boiler safety device is described as spring-adjusted to 13 bar. On Linea PB Man.10.1 V3.2 (12/2015) and Man.10.1.04 V5.1 (12/2024), the matching heat-up procedure and Note both use 11–12 bar. Across these manuals, brewing 9 bar (and the 0–12 bar operating band) is a separate role from the heat-up expansion ceiling.

This reading does not decide whether every La Marzocco model shares Strada’s internal split, whether 13 bar is wrong and 11–12 right (or the reverse), whether the heat-up reading equals brew pressure at the puck, or whether the Note’s calcium-cleaning / cap-adjustment wording should be followed as a how-to. Only these three operating manuals are used for the ceiling comparison. Home-machine flow-rate pages already treated elsewhere on this site are not re-examined. No measurement here repeats the heat-up observation.