FAQ
TL;DR: Most thermostatic heads have a 16°C anti‑frost stop; as one pro notes, "does not close below 16 degrees." To remove a radiator mid‑season you need the system drained or pipe freezing, even with a return shut‑off. [Elektroda, stanislaw1954, post #18497252]
Why it matters: Apartment residents on central heating need safe, compliant ways to isolate or replace radiators without flooding or breaking co‑op rules.
Quick Facts
- Many thermostatic valves won’t fully close; some stop at about 16°C to prevent freezing. [Elektroda, Zbigniew Rusek, #18493662]
- Without a return (outlet) shut‑off valve, you can’t remove a radiator from a filled system. [Elektroda, Zbigniew Rusek, #18493662]
- Closing only the supply? Expect water to “flow in from behind” via the return. [Elektroda, stanislaw1954, post #18493562]
- Co‑ops often ban pre‑radiator shut‑offs to protect heat‑metering and stop radiator swaps; wait for the seasonal drain. [Elektroda, Wojewoda82, post #18496639]
- Rooms can exceed 16°C from sun or neighbor heat, so a 16°C‑limited head may still shut. [Elektroda, Zbigniew Rusek, #18498270]
Can a thermostatic valve fully shut off my radiator?
Yes, on the supply (hot) side, if the model allows full closure. Some heads limit closure to about 16°C for anti‑frost protection. That limit prevents total shutoff in cooler rooms. You still need a return shut‑off to isolate the radiator for removal. [Elektroda, Zbigniew Rusek, #18493662]
How do I close a thermostatic head—do I just set it to 0?
Yes. Turn the thermostatic head to 0 to close the supply side for that radiator. This is the normal user operation. For service isolation, also close a return shut‑off if fitted. If no return shut‑off exists, the radiator remains connected to the system. [Elektroda, stanislaw1954, post #18493607]
If I close only the supply valve, will the radiator empty by itself?
No. Water will still enter from the return side. “Water will flow in from behind.” You must also close a return shut‑off to stop flow. Without it, the radiator stays pressurized by the return line. This is why two valves are used for safe isolation. [Elektroda, stanislaw1954, post #18493562]
Can I put a thermostatic valve on the return (outlet)?
No. “There are no thermostatic valves on the return (it makes no sense).” Install the thermostatic valve on the supply. Use a simple shut‑off (service valve) on the return if your building rules allow it. That combination supports control and maintenance. [Elektroda, stanislaw1954, post #18494628]
What valve do I need on the return to remove a radiator?
A return shut‑off valve. Without it, you cannot remove the radiator while the installation is filled. The return remains under pressure, so closing only the supply is insufficient. Fit a return service valve if permitted, or plan for a system drain. [Elektroda, Zbigniew Rusek, #18493662]
How do I isolate a radiator for replacement (3 steps)?
- Turn the thermostatic head on the supply to 0.
- Close the return shut‑off valve.
- Drain the radiator locally, then loosen the unions and remove it.
These steps assume both valves exist and are functional. Otherwise, wait for a system drain. [Elektroda, stanislaw1954, post #18493607]
Why does my cooperative forbid shut‑off valves before radiators?
To protect heat‑metering and prevent radiator swaps during the heating season. Some people might keep a second radiator without a divider to game costs. Buildings then require you to wait until the system is drained at season’s end for changes. [Elektroda, Wojewoda82, post #18496639]
I only want to paint behind the radiator—can I remove it mid‑season?
Usually no. If only thermostatic heads are allowed, many “do not close below 16°C.” Even with a return shut‑off, you still need the system drained or to freeze the pipes to remove it safely. Plan work for the off‑season when possible. [Elektroda, stanislaw1954, post #18497252]
My room is warm from sun and neighbors. Can a 16°C‑limited head still close?
Yes. If the room stays above 16°C, the thermostatic head can close the supply even in winter. “This may even occur in winter.” Solar gains or adjacent heated flats can raise ambient temperature above the anti‑frost threshold. [Elektroda, Zbigniew Rusek, #18498270]
Are return valves for balancing or just isolation?
They primarily isolate radiators for leak repairs or replacement. Balancing is typically handled at the supply via thermostatic valves. Cast iron radiators have low leak risk; panel radiators are more vulnerable. “Return valves are intended to enable the radiator to be isolated.” [Elektroda, Zbigniew Rusek, #18495954]
Is there pressure on the return line too?
Yes. “Remember that the pressure is not only on the supply, but also on the return.” Closing only the supply will not depressurize the radiator. This is why a return shut‑off is essential for safe isolation. [Elektroda, Zbigniew Rusek, #18493662]
What’s the risk of swapping radiators without draining the system?
Flooding. As one expert warns, “maybe he will flood his apartment.” Cooperatives empty the central heating at season’s end; plan work then. Attempting mid‑season work without isolation risks water damage and violations of building rules. [Elektroda, Wojewoda82, post #18496639]
Can I install a thermostatic valve on the outlet and cap it to bypass rules?
That attempts to bypass the stated regulation. “If you install a thermostatic valve on the drain (outlet) ... you will bypass their regulation.” Confirm any changes with your cooperative in writing before proceeding to avoid penalties. [Elektroda, palmus, post #18494783]
and close if necessary.