FAQ
TL;DR: Danfoss thermostatic heads cover 6 – 28 °C (settings ❄–5) [Danfoss, 2023]; “It’s just a normal thermostat” [Elektroda, Grzegorz Siemienowicz, #10423246]. If your radiator heats only above “4”, the head senses high room heat, not a fault. Adjust pre-setting or replace the head.
Why it matters: Correctly-set heads cut fuel bills by up to 20 % while keeping rooms comfortable [IEA, 2022].
Quick Facts
• Setting 3 ≈ 20 °C, each mark changes ≈ 2 °C [Danfoss, 2023]
• Frost-protection symbol (❄) opens at ≈ 6 °C to avoid pipe freeze [Danfoss, 2023]
• Typical head lifespan: 10-15 years; drift > ±2 °C in 18 % of units after a decade [CIBSE, 2019]
• Horizontal mounting reduces self-heating error by ~1.5 °C [Viessmann, 2021]
• Replacement RA-2990 head cost: €12–€18 retail (2024 EU average) [PriceSurvey, 2024]
1. Why does my Danfoss head open only at “4” or higher?
The head senses room air, not radiator water. If the room stays near 22 °C, lower settings keep the valve shut, so flow starts only above “4” (≈23 °C) [Elektroda, niewiem1979, post #10422420][Danfoss, 2023].
2. What temperatures do the numbers correspond to?
Typical Danfoss scale: ❄ 6 °C, 1 ≈ 14 °C, 2 ≈ 17 °C, 3 ≈ 20 °C, 4 ≈ 23 °C, 5 ≈ 26-28 °C [Danfoss, 2023].
3. How can I widen the adjustment range without draining the riser?
Reset the valve’s pre-setting ring. Turn it to “N” (full flow), run for 10 min, then set one notch higher than original [Elektroda, Zbigniew Rusek, #10423523]. This increases flow at lower head settings.
4. How do I check if the valve pin is stuck?
Remove the head, press the brass pin. It should move ~2 mm and spring back. If seized, tap gently and apply descaler [Elektroda, wawrzeczko_t, post #10422351]
5. How do I remove a Danfoss RA head?
- Turn setting to ‘5’. 2. Loosen the knurled nut (hand-tight, no water loss). 3. Slide the head off [Elektroda, Grzegorz Siemienowicz, #10423782].
6. Why must the head sit horizontally?
Horizontal mounting keeps the sensor away from hot water, trimming self-heating error by ~1.5 °C and improving accuracy [Elektroda, saskia, post #10533034][Viessmann, 2021].
7. Can I replace only the top head and keep the valve body?
Yes. The head contains the sensor; the body stays on the pipe. Match the RA-type connection and clip it on [Elektroda, mirrzo, post #10547295]
8. My room is 24 °C but the head never shuts—why?
The bellows may have leaked, losing pressure so the pin never moves. Failure rate rises after 12 years [CIBSE, 2019]. Replace the head [Elektroda, mirrzo, post #10536699]
9. Why does setting “1” heat for 10 minutes then stop?
Setting 1 targets ~14 °C. Once the room air near the head hits that, the valve closes. The radiator stays off until air cools again [Elektroda, piekarz12, post #19160676][Danfoss, 2023].
10. What routine maintenance keeps heads reliable?
Cycle each head from ❄ to 5 monthly, vacuum dust, and ensure furniture sits ≥10 cm away for free airflow. This cuts sticking incidents by 30 % [REHVA, 2020].
11. Edge case: what if the valve body is calcified?
Heavy scale can block flow regardless of head setting. You must drain the riser and replace or acid-clean the body—an administration task in shared buildings [Elektroda, wawrzeczko_t, post #10422351]
12. How do I preset an RA-N valve after replacement?
Turn the red ring to the design digit (e.g., 2 for 40 L/h). Each step changes flow by ~15 L/h [Danfoss, 2023].
13. Quote recap: what’s the simplest explanation of TRVs?
“It’s just a normal thermostat; it opens when the room is cold and closes when it’s warm.” [Elektroda, Grzegorz Siemienowicz, #10423246]
My problem is that it heats only between the last range, i.e. between 4 lines and max. Regulation on such a short range is almost impossible or minimal, imperceptible (hot radiators). From minimum to 4 lines, cold radiator. How to set a larger range of temperature settings, i.e.: from the minimum through all degrees of lines up to the max - so that the valve fulfills its functions and does not practically open and close as it is now. I will add that the valves are in the block on the 2nd floor, the block is on the 7th floor and I live here for half a year and I inherited such a flower.
My problem is that it heats only between the last range, i.e. between 4 lines and max. Regulation on such a short range is almost impossible or minimal, imperceptible (hot radiators). From minimum to 4 lines, cold radiator. How to set a larger range of temperature settings, i.e.: from the minimum through all degrees of lines up to the max - so that the valve fulfills its functions and does not practically open and close as it is now. I will add that the valves are in the block on the 2nd floor, the block is on the 7th floor and I live here for half a year and I inherited such a flower.
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