Last Updated on 15 July 2025 by Maelle
In a wet central heating system, a boiler heats the water before it is pumped through a circuit of pipes to the radiators installed throughout the house. Each radiator is equipped with valves that control the water flow, which regulates the time the water spends in the radiator and the amount of heat it releases. When the water leaves the radiator, it is returned to the boiler to be reheated.
Some heat is lost through the pipes as the water circulates through the system, but this loss is minimized thanks to the narrowness of the pipes and the speed at which the water circulates. A well-designed system may have several short circuits leading from the pump, rather than a single large circuit, to ensure that the last radiator in each circuit heats as efficiently as the first. Today, tout-reparer.fr offers you its guide: How to repair your apartment radiator? How to Bleed a Radiator
Keeping your radiators well maintained will save energy as they run more efficiently. If your radiator is cold at the top but hot at the bottom, it means there is air in the system and you need to bleed your radiators.
Before you start
Never bleed your radiators when they are hot, as scalding water could escape.
You will need:
A radiator bleeder key or a flathead screwdriver
- A cloth
- Step One
Turn off your central heating and allow the radiators to cool. Start with the ground floor radiators, starting with the first radiator in the circuit.
Step Two
All radiators are equipped with a vent valve in a top corner to allow trapped air to escape. It’s a square shaft inside a threaded cap (a round hole with a square inside). Use a radiator vent key (or in some cases a flathead screwdriver) to turn the shaft counterclockwise to open the valve. This should be between a quarter and a half turn—do not unscrew it more than a full turn.
Step Three
You will hear the hiss of trapped air escaping. Hold a cloth under the valve to catch the water, and as soon as the first trickle appears, close the valve by turning the vent key clockwise.
Check all your radiators, as you may need to bleed more than one. Start with the ground floor radiators, then move on to the upstairs radiators and bleed them one by one if necessary.
Turn your system back on and re-pressurize the boiler if necessary. The manufacturer’s manual should explain how to do this. Your radiators should now be working more efficiently. If you need to bleed your radiators frequently, have the system checked by a heating engineer such as milton-habitat-solutions.com, as there is likely a fault somewhere allowing air to enter the system.
How to Fix a Noisy Central Heating System Controls vary between boiler makes and models, so be sure to keep your boiler’s operating instructions in a handy place in case of a problem. Many faults have simple solutions, which you should be able to fix yourself—but if in doubt, call an engineer. How to Fix Squeaky PipesPossible Cause: Hot pipes expand and rub against the floor, walls, or other pipes.
What’s the solution? Widen the pipe notches in the joists (but don’t deepen them, as this will weaken the joists), clip unsupported pipes, or place insulation around and between the pipes.
How to fix buzzing noises in pipes Possible cause: The pump speed may be too high or your pipes may be too narrow for the system’s flow rate. What’s the solution? Call an engineer. How to fix flowing noises in pipes Possible cause: Air or gas bubbles in the system.
What’s the solution? Bleed the radiators (see
How to Bleed a Radiator ) and if the problem persists, call an engineer. How to fix whistling and/or knocking noises?
Possible cause 1: Faulty boiler thermostat. What’s the solution? Call an engineer to check. Possible cause 2: Limescale buildup. In areas with hard water, limescale can build up in the system and cause the noise. What’s the solution?
Call an engineer to clean it. They may decide to install a hard water filter to prevent this from happening again.
Tip: Protect your system
For long-term protection against corrosion and limescale buildup, we recommend cleaning your system with a central heating cleaner and then protecting it with a central heating protector.
How to fix a cold radiator?
If your boiler is still working properly but you’re experiencing cold radiators, there could be several reasons.
How to fix your radiators when they’re all cold? Possible cause 1: Your pump isn’t working.What’s the solution? See Whistling and/or popping noises.
Possible cause 2: Your pump’s thermostat or timer is incorrectly set or faulty.
What’s the solution? Check and reset if necessary. If the thermostat or timer is set correctly, turn off the power and check the wiring connections, making sure to follow the operating instructions. If the problem persists, call a technician.
How to fix your radiators when some of them are cold?
Possible cause 1: The thermostat or timer on your zone valve is incorrectly set or faulty.
What’s the solution? Reset it. If it is set correctly, turn off the power and check the connections, referring to the operating instructions. If the problem persists, call a technician.
Possible cause 2: The system may be unbalanced and needs to be balanced. Balancing involves adjusting all the radiator valves to ensure that all the radiators heat at the same time.
What’s the solution? Call an engineer to balance the system. Possible Cause 3: The zone valve itself may be defective. What is the solution? Replace the zone valve with a new one.
How to Fix a Cold Radiator
Possible Cause 1: The manual radiator control valve is closed.
What is the solution? Open/reactivate the valve.
Possible Cause 2: The thermostatic radiator valve (TRV) may be incorrectly adjusted.
What is the solution? Reset it.
Possible Cause 3: The thermostatic radiator valve may be defective.
What is the solution? Replace the TRV with a new one.
The entire team at the blog
tout-reparer.fr
is available to help you in the blog’s comments section.
