Boiler-based commercial coffee machines live in heat, steam and vibration — an environment where simple, sealed mechanical thermostats still earn their place. A capillary thermostat has no electronics at the hot end: the sensing bulb sits in or on the boiler, the capillary carries the signal, and the switch body mounts where it stays cooler and drier. This guide covers the two thermostat jobs in a coffee machine — boiler control and safety limiting — and how to specify each.
Two jobs: control and protection
The control thermostat cycles the boiler element to hold steam pressure and temperature through the service day. It switches constantly, so it is specified for electrical endurance — our control family is tested to a mechanical life of 100,000 cycles. The safety limiter is a separate, independent device that does nothing unless the control fails: then it cuts power to the element before the boiler can run away. One machine, two devices, two different specifications — never let one part try to do both jobs.
Control thermostat selection
Start with range and rating. The AG16-K control covers 50–400°C at 16A / 20A (110V / 250V), far beyond boiler duty on paper — what matters is that your working point sits comfortably inside the calibrated range, because accuracy is best away from the ends of the scale, and an oversized range costs dial resolution. We configure setpoint ranges to order, so tell us the machine’s actual operating temperature rather than accepting a generic range. For contacts, SPST switches the element circuit alone; SPDT adds a second circuit for a pilot light or alarm from the same control. Where the machine’s interior leaves no room for a standard body, the AGO series offers the same 16A / 20A ratings and 50–400°C range in a compact form factor.
The safety limiter: manual reset, on the boiler
Fit a manual-reset limiter — AG16-S, TY316-8 or WQB — with its own bulb on the boiler. Manual reset is deliberate: if the limiter ever trips, the machine stays off until a technician finds out why, instead of quietly re-arming itself between services. Trip points are factory-set; on boilers the limiter is specified against the boiler’s maximum safe temperature rather than its working temperature, and we calibrate to your specification. Limiters are rated for rare trips (6,000 cycles) precisely because a trip is a fault event, not a control action.
Steam, water and tight spaces
Coffee machines leak, drip and get descaled; steam finds every panel joint. Three practical points follow. First, keep the switch body out of the wettest zone and let the capillary do the travelling — that separation is the whole point of the technology. Second, where the control itself must sit in a damp location, the TY316 is available in a waterproof version. Third, order the capillary length for the real route inside the machine, with gentle bends and slack for servicing the boiler — lengths are configured to order, and the routing rules in our installation guide apply unchanged. Bulbs belong fully seated in the boiler thermowell, in firm metal-to-metal contact, so the control reads boiler temperature rather than a lagging blend of boiler and ambient.
Certifications
Our thermostats are produced under a TÜV-certified quality system — certificate R50309054 (EN 60730-1 / EN IEC 60730-2-9), verifiable on Certipedia. Confirm the approvals carried by the specific models you select for the markets you sell into.
Building a new machine, or re-specifying the thermostats on an existing one? The same factory that makes the control and limiter also configures them for OEM supply — setpoints, capillary lengths, bulbs and private labelling are covered in our OEM and private label guide.
FAQ
Does a coffee machine need both a control thermostat and a safety limiter?
Yes. The control regulates boiler temperature in normal service; the limiter is an independent backup that cuts power only on a fault. They are separate devices with separate bulbs, and the limiter should be manual-reset so a trip forces a service check.
Can setpoints and capillary lengths be customised for my machine?
Yes. As an OEM manufacturer we configure setpoint ranges, capillary length, bulb size and knob format to your equipment — send the operating temperature and the bulb-to-panel distance and we will propose the configuration.
Is there a waterproof thermostat option for wet areas?
Yes — the TY316 control is available in a waterproof version. More often, though, the better design is to keep the switch body in a dry zone and let the capillary and bulb reach into the wet area.
Capillary Control Thermostats · Manual Reset Safety Limit Thermostats · OEM Thermostats and Private Labelling