Cold radiators after switching on: what to do

If you’re wondering “cold radiators what to do” after switching on the heating, start with simple checks: air in the radiators, boiler pressure, radiator valves and the thermostat. In Milan this often happens at the first autumn switch-on after months of the system being idle. Below are safe steps to follow without attempting risky fixes.

Cold radiators: what to do in the first minutes

Before assuming a fault, check whether the issue affects a single radiator or the whole apartment.

• Make sure the heating thermostat is on and set above room temperature.
• Open the radiator valve fully and, if present, the thermostatic valve.
• Wait at least 20–30 minutes: after switching on the system it can take time for heat to circulate.
• If only the top stays cold, there is probably air that needs to be bled out.

Air in radiators and boiler pressure

When radiators don’t heat evenly, you often need to bleed them. Turn the system off, wait until the radiators are warm but not hot, and open the bleed valve slowly with a bowl underneath. Close it as soon as a steady stream of water comes out.

After bleeding, check the gauge: low boiler pressure can prevent proper circulation. If you don’t know how to restore pressure or it drops again, it’s better to book an hourly plumber for a check.

Stuck valves and the thermostat: signs not to ignore

After months of inactivity, stuck radiator valves can remain closed even if the knob turns. Don’t force them with pliers or hammering: you risk causing leaks.

If all radiators stay cold, check the boiler, the programmer/chronothermostat and the power supply. A switched-off thermostat, dead batteries or faulty connections can prevent the system from starting. For electrical doubts it’s safer to book an electrician, while leaks or valve issues require an plumber. For local context, also read when to call a plumber in Milan.

When to call a professional

Call a technician if you hear unusual noises, find water near the radiator, the pressure frequently drops, or no radiator heats up. Avoid opening the boiler or working on gas yourself. A radiator plumber can safely check bleed valves, radiator valves, circulation and minor leaks.

Frequently asked questions

Why is the radiator warm at the bottom and cold at the top?

That usually means there is air trapped in the radiator. You can try bleeding it with the system off and the radiator not scalding hot. If it recurs often, there may be a pressure or circulation issue.

What pressure should the boiler have?

The correct value depends on the boiler model and the heating system. Check the boiler manual. If the pressure is too low or falls quickly after topping up, have a technician inspect the system.

Can I free a stuck radiator valve myself?

You can check that the knob is open, but avoid forcing it. If the valve is stiff, leaking or not allowing water through, it’s better to call a plumber to avoid damaging the radiator.

With the Cura24h app (App Store and Google Play) you can quickly book a professional to check radiators, valves and the heating system. App Store · Google Play