Commercial pressurestat for 110~120/220~240V equipment, #P302-6. This is the part that regulates your boiler heating via a diaphragm that expands and contracts as the boiler steam pressure raises and lowers, activating the contacts and sending a signal to the heating element telling it to turn on or off. It is by far the most commonly used pressurestat.

Of course in most cases any presurestat will work, but if there is room for it go with the Sirai. It is a purely mechanical part, and so there's no micro-switch to go out. The diaphrams go bad, and the contacts get fried. But the Sirai is essentially two or three pressurestats, depending on how many wires are used in your unit. There are six connections. When the contacts on the first set of contacts go bad, simply move the two wires over to the next available unused set.

CE-SEV-ASE-UL approved ISO 228 G connection 1/4"M for pipe ø 4x6 mm adjustable scale 0.5÷1.4 bar fixed differential 0.15 (± 0.06) bar fluid temperature max: 140°C max contact load: 220V 7KW (30A)

Factory specification sheet here

Cross-references:

Part number	Manufacturer
20150	ASTORIA CMA
7433001	BEZZERA
5006010	BFC
00630.4.00.08	BRASILIA
000399	BRUGNETTI-AURORA
95.00275	CARIMALI
531-190-310	CIMBALI
00049035	ELEKTRA
558	ESPRESSO RESOURCE
60000000	EXPOBAR
60000005	EXPOBAR
2231116597	FAEMA
2231131900	FAEMA
531190310	FAEMA
5.2.000.0680	FIEMMA RST
A2100050	FIORENZATO C.S.
A2100314	FIORENZATO C.S.
FC1669	FRACINO
07935703	FUTURMAT-ARIETE
12001274	GAGGIA
WGADM0541	GAGGIA
07935703	GAGGIA SPAGNA (SPAIN)
1160800015	GRIMAC
1160800016	GRIMAC
A2100314	GRIMAC
GR814	GRIMAC
GR815	GRIMAC
GRC615	GRIMAC
V070	GRIMAC
07935703	ITALCREM
10060660	LAVAZZA
10066203	LAVAZZA
07935703	MAIRALI
L270	MARZOCCO
20150	MCE
09200006	NUOVA SIMONELLI
D20150	ORCHESTRALE
451301	PAVONI
34200110	RANCILIO
34200111	RANCILIO
9005050	RENEKA
GR814	RICAMBI GARDOSI
GR815	RICAMBI GARDOSI
GRC615	RICAMBI GARDOSI
V070	RICAMBI GARDOSI
5006010	ROYAL
SVTMP010	SAB ITALIA
1200127	SAECO
WGADM0541	SAECO
108007	SAN MARCO
10602010	SANREMO
10602010A	SANREMO
C-0455	SCALA
01101	SPAZIALE
02623	SPAZIALE
ELETPRE	VIBIEMME
09200006	VICTORIA ARDUINO
07935703	VISACREM
W10440	WEGA
WY20150	WEGA

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Appia II Boiler

Sirai P302 30A Presssurestat