Short & direct
If your radiator is noisy and stays cold, there is usually trapped air in the system. You can bleed a radiator yourself with a bleed key: open the thermostat fully, switch off the pump and open the top valve until water comes out instead of air. Then check the pressure and top it up to 1–2 bar if needed.
When your radiator gurgles, hisses and still stays cold, the cause is usually trapped air in the system. The good news: in most cases you can bleed a radiator yourself – with a little patience and the right tool. This guide walks you through it step by step and explains when it is time to call a professional.
Why Is the Radiator Noisy and Cold?
When air collects in the heating circuit, it rises to the top and blocks the flow of water inside the radiator. As a result, hot water no longer reaches the upper section, the radiator stays partly or completely cold, and you hear those typical gurgling sounds. Especially at the start of the heating season here in the Zurich Limmattal region, this is a very common issue.
How to Bleed a Radiator: Step by Step
With a bleed key (available at any hardware store for a few francs) you can sort this out in minutes. Here is how:
- Open the thermostat fully – set all radiator valves to maximum so the water can circulate freely.
- Switch off the circulation pump – turn the heating pump off so the air can collect at the top. Wait around 30 to 60 minutes.
- Have a container ready – hold a cloth or a small bowl under the bleed valve, as some water may escape.
- Open the top valve – fit the bleed key to the valve at the top of the radiator and turn slowly. You will hear the air hissing out.
- Wait until water comes – as soon as a steady stream of water appears instead of air, close the valve again.
- Check the pressure and top up – read the system pressure on the gauge. If it is below the target, carefully add water until it reaches 1–2 bar.
- Switch the pump back on – restart the circulation pump and check whether the radiator now heats evenly.
Tipp: Always start with the radiator furthest from the boiler and work your way towards it. This is the most reliable way to clear all the trapped air.
Pressure Keeps Dropping? Time for a Professional
If the pressure drops quickly again after topping up, or the radiator stays cold despite repeated bleeding, there is a bigger problem at play – such as a faulty expansion vessel, a defective pump or a leak in the system. In these cases only proper heating maintenance will help. Our heating engineers in the Limmattal track down the cause and fix it reliably. Learn more on our heating page.
Regular Maintenance Prevents Problems
An annual maintenance service makes sure that air, dirt and wear never become a problem in the first place – saving energy and extending the life of your system.
Heating Breakdown in Winter? We Are Here for You
If your heating fails completely in the middle of winter, do not wait too long. Our 24/7 emergency service covers the entire Limmattal – from Dietikon through Schlieren to Urdorf – arriving quickly to bring your warmth back.
Heating cold, or would you like a free quote? Call us on 044 747 06 61 – around the clock.
Need help from a professional?
Free quote or 24/7 emergency – we are here for you in the Limmattal.