The Caleffi 203502 is a self-powered thermostatic control head with a remote contact probe on a 78 in (2 m) capillary, adjustable from 68 to 122°F (20 to 50°C). The sensing element is placed in contact with, or immersed in, the medium so the head holds the fluid temperature at the dial setting rather than sensing room air. It needs no wiring, power supply or controller.
Best for fixed-point temperature limiting on a circuit, such as capping the feed to a radiant panel injection circuit or a domestic hot water preparation circuit.
Specifications from Caleffi datasheet 01034/23 NA (replaces 01034/19 NA) and installation instructions 28009.02. Reviewed August 2026.
Key Features
Senses Fluid Temperature, Not Room Air
The sensing element reads the temperature of the medium it is placed in, not room air. This is a fixed-point regulator for a circuit, not a room thermostat.
Self-Powered Operation
A liquid-filled element expands as the sensed fluid warms and throttles the valve closed. No wiring, transformer or controller is required.
68 to 122°F Setting Range
Graduated dial marked 68, 75, 85, 95, 105, 110 and 122°F, with restriction and locking so a commissioned setpoint cannot be disturbed.
78 in Capillary
The 2 m capillary lets the sensing element sit at the measuring point while the adjusting head stays accessible on the valve.
Mounting Accessories, Ordered Separately
Caleffi lists the 475001 contact support (L = 167 mm) and the 475002 sensor well (1/2 in connection, 13 mm diameter, L = 187 mm) for use with the 203502. Neither is supplied with the head.
Couples to Caleffi Valve Bodies
Listed by Caleffi as a control head option for the 220 and 221 series thermostatic radiator valve bodies, using the documented M30 x 1.5 head connection.
Technical Specifications
| Product Type | Thermostatic Control Head |
| Series | 203 Series |
| Head Type | Contact probe |
| Element type | Liquid-filled |
| Setting temperature range | 68 to 122°F (20 to 50°C) |
| Max. sensor temperature | 212°F (100°C) |
| Max. pocket pressure | 150 psi (10 bar) |
| Max. differential pressure | Determined by the valve body |
| Length of capillary | 78 in (2 m) |
| Valve connection | M30 x 1.5 |
| Overall height | 3-1/8 in |
| Diameter | 2 in |
| Probe diameter | 7/16 in |
| Probe length | 6-1/4 in |
Documentation
Related Products
- Caleffi 200000 : Control Head, Built-in Sensor
- Caleffi 201000 : Control Head, Remote Sensor
- Caleffi 472000 : Control Head, Remote Knob
- Caleffi 449010 : Manual Knob
Frequently Asked Questions
What does the Caleffi 203502 do?
It is a self-powered thermostatic control head fitted with a remote contact probe. The sensing element reads the temperature of the medium it is placed in and the head throttles the valve to hold that temperature at the dial setting. It does not sense room air.
Is the Caleffi 203502 a room thermostat?
No. The 200, 201 and 472 series heads sense room air and control comfort. The 203502 senses medium temperature at the pipe and works as a fixed-point regulator to cap or control the temperature delivered to a circuit.
What temperature range does the Caleffi 203502 cover?
The setting range is 68 to 122°F (20 to 50°C). Maximum sensor temperature is 212°F (100°C) and maximum pocket pressure is 150 psi (10 bar).
Which valve bodies does the Caleffi 203502 fit?
Caleffi lists it as a control head option for the 220 and 221 series valve bodies, using the M30 x 1.5 head connection given in its dimension table.
How is the probe on the Caleffi 203502 mounted?
The sensing element is placed in contact with, or immersed in, the medium. Caleffi lists the 475001 contact support and the 475002 sensor well for this head; both are ordered separately.
- Product Type:
- Thermostatic Control Head
- Product Family:
- Thermostatic Control Heads
- Series:
- 203 Series
- Head Type:
- Contact Probe
- Setting Temperature Range:
- 68 to 122 deg F (20 to 50 deg C)
- Capillary Length:
- 78 in (2 m)
- Valve Connection:
- M30 x 1.5
- Element Type:
- Liquid-Filled
