For a suitable underfloor heating actuator, the operating voltage, valve connection or adaptor, and unpowered position must match the existing controls. NC means normally closed, NO normally open. The same connection thread or a 230 V rating alone is therefore not enough to select a replacement. The best starting point is the designation of the old actuator and the underfloor heating manifold.
What do NC and NO mean?
The abbreviations describe the intended state without electrical actuation: an NC actuator closes when unpowered, while an NO actuator opens when unpowered. The controls must support the appropriate operating action. The two versions are therefore not freely interchangeable, even if their housings look identical.
The visible position of a brand-new actuator need not yet match its later unpowered operating state. Some models have a First-Open function for commissioning. The documentation explains whether a particular actuator has this function and how the manufacturer describes it. Do not assume that a function on another model also applies.
230 V or 24 V: the existing controls determine the choice
Do not base the operating voltage on an assumption about the building. Read the rating plate and documentation for the old actuator and the controls. A 24 V actuator must not be connected to a terminal intended for 230 V. The other electrical specifications and the acceptability of the combination must also be checked.
Photos of accessible markings are enough for your enquiry. Do not open electrical connections or live housings to obtain them. Wiring, electrical testing and commissioning are carried out by a qualified electrician or an appropriately qualified installer.
Why M30 × 1.5 alone is not a complete compatibility check
The thread describes one part of the mechanical connection. However, correct valve operation also depends on the intended valve interface and the actuator's technical requirements. Some manufacturers use their own adaptors. Möhlenhoff describes its controls as a system with matched components; at Selfio, a particular actuator is explicitly assigned to a specific valve interface.
Therefore include the product designation of the manifold or valve. If an existing adaptor is to be used, include its marking in the enquiry too. A similar-looking adaptor is no evidence that the actuator will open and close the valve correctly.
These details help when replacing an actuator
| Detail | Where can you find it? |
|---|---|
| Manufacturer and article number | The rating plate of the old actuator, invoice or technical documentation. |
| Operating voltage | Actuator marking and controls documentation. |
| NC or NO | Product designation or data sheet; do not infer it solely from the current position. |
| Manifold or valve | Manufacturer, type and photo of the accessible marking. |
| Connection or adaptor | Existing designation and manufacturer approval for the combination. |
| Controls | Designation of the room thermostat or wiring centre. |
Also note the required quantity and the reason for replacement. A cold room alone does not prove an actuator is faulty: controls, flow or other system conditions can also play a part. Have the cause established before replacing several parts on suspicion.
Frequently asked selection questions
Can I replace NO with NC?
Only if the particular controls and valve combination are designed for it and the installer ensures the correct operating action. Matching voltage and design do not amount to approval.
Does every 230 V actuator fit my manifold?
No. Voltage, mechanical adaptation and controls must all match. Include the manufacturer and type details.
Do I have to replace all actuators at once?
This depends on the condition, cause of the fault and system compatibility of your installation. A single fault does not imply a blanket obligation to replace every circuit's actuator.
Enquire about suitable components
The available components are under Underfloor heating. The roles of the manifold, cabinet and fixing system are explained in our Component selection guide. Send us the markings from your system before choosing parts; details of the process are under Collection and enquiry.