FAQ
TL;DR: Thermostatic heads shut when room heat is already near the dial’s setpoint; e.g., setting 4 ≈ 24°C. “Below 24 °C, it will start heating at ‘4’.” [Elektroda, marqqv, post #16837207]
Why it matters: If some radiators stay cold while one overheats and hums, you can fix comfort and noise by matching settings to actual room temperature and basic checks.
Quick Facts
- Dial guide (typical): 0=off, *=~7°C, 1≈12°C, 2≈16°C, 3≈20°C, 4≈24°C, 5≈28°C. [Elektroda, marqqv, post #16837207]
- Snowflake/“*” is anti-freeze mode (~7°C) to prevent freezing in seldom-used rooms. [Elektroda, marqqv, post #16837207]
- Home systems need a circulating pump for thermostatic heads to regulate flow. [Elektroda, Szyszkownik Kilkujadek, post #16826722]
- At 24°C room temp, a head on “4” remains closed until the room cools a bit. [Elektroda, marqqv, post #16839425]
- Cheap thermometers can read off by 1–2°C; verify before chasing faults. [Elektroda, Adam-T, post #16839450]
Why are radiators 1–4 cold while the 5th is too hot and humming?
Your rooms are likely already near or above each head’s setpoint, so the valves close. The hot, humming radiator is the one still open, taking most flow; the noise is water rushing or a closed valve “rustling.” “Start with the room temperature.” [Elektroda, marqqv, post #16837207]
How do I test if ambient temperature is making the head close immediately?
Use a quick cool-down test: 1) Close the room door and set the head to snowflake. 2) Ventilate to about 10°C. 3) Turn the dial slowly upward and note the number where heating starts. That number should match expected temperatures on the scale. [Elektroda, marqqv, post #16839466]
What temperatures do 1–5 correspond to on Ferro GT 20 heads?
Typical mapping: 1≈12°C, 2≈16°C, 3≈20°C, 4≈24°C, 5≈28°C. The snowflake holds around 7°C to prevent freezing. Use this table to set comfort targets per room. [Elektroda, marqqv, post #16837207]
Do I need a pump for thermostatic heads in a house?
Yes. In single-family homes, thermostatic heads assume a circulating pump. Without a pump, regulation fails and rooms won’t heat evenly. Confirm your pump runs and is correctly set. [Elektroda, Szyszkownik Kilkujadek, post #16826722]
Could air in the system or low pressure stop my radiators from heating?
Yes. If the installation has air or pressure is low, flow drops and radiators stay cold. Bleed the radiators and verify system pressure before blaming the heads. [Elektroda, Szyszkownik Kilkujadek, post #16826722]
Why does nothing happen on setting 4 when my room is 24°C?
Because setting 4 targets about 24°C. At that temperature, the valve stays closed until the room cools slightly. This is normal operation for comfort control. [Elektroda, marqqv, post #16839425]
My thermometer shows 26.8°C and radiators on “3” are cold—normal?
Yes. Setting 3 targets about 20°C. At 26.8°C, heads close immediately and radiators cool. Reduce heat sources or lower the boiler output to maintain comfort. [Elektroda, joan-rz, post #16837349]
Can my room thermometer be lying and cause wrong conclusions?
Yes. A basic thermometer may be off by 1–2°C. Cross-check with another meter before adjusting valves or calling service. Small errors can change how heads behave. [Elektroda, Adam-T, post #16839450]
Which gear is discussed in this thread?
Ferro GT 20 thermostatic heads were installed on radiators, and the boiler was a Defro with a feeder. Match your setup when comparing behavior. [Elektroda, joan-rz, post #16828803]
How should I set for a typical comfort range around 23–25°C?
Use setting 4. It should maintain roughly 23–25°C when the room needs heat. Fine-tune one notch if you feel too warm or cool. [Elektroda, marqqv, post #16837397]
What does the snowflake symbol do in practice?
Snowflake holds a frost-protection level near 7°C. Use it in spare rooms or during long ventilations to prevent freezing without heating the space. [Elektroda, marqqv, post #16837207]
Why do my valves hum or rustle? Is it harmful?
Noise often means the valve is closed or nearly closed while water tries to pass. It signals throttling, not damage. Reduce pump speed or slightly adjust settings. “It’s rustling because it’s closed.” [Elektroda, marqqv, post #16837207]
Could the head and valve be mismatched if it shuts off immediately?
If the valve and head came as a set, they should match. If behavior seems wrong after checks, return to the store and test or file a complaint. [Elektroda, marqqv, post #16839425]
Three heads work and five don’t—what should I try first?
Verify room temperatures and dial targets, then repeat the cool-down test for a non-working radiator. If purchased as a set, ask the seller to test a sample unit with you. [Elektroda, marqqv, post #16839425]
What’s a quick 3‑step reset for puzzling head behavior?
- Set the head to snowflake and bleed the radiator. 2. Confirm pump operation and system pressure. 3. Cool the room, then raise the dial until heat starts, noting the number. [Elektroda, Szyszkownik Kilkujadek, post #16826722]
