Radiators are designed to heat evenly from top to bottom, so it can be frustrating when the top stays cold while the bottom feels hot. This is a fairly common issue in homes across Bedford and Milton Keynes, and while it often has a simple fix, it can also be a sign that your heating system needs maintenance. Addressing it promptly can improve efficiency, reduce energy use, and prevent further wear on your boiler.
Why Radiators Go Cold at the Top and How to Resolve It
Trapped Air in the Radiator
Over time, small amounts of air can enter a central heating system through pipe joints, during water refills, or as a natural by-product of corrosion. Because air is lighter than water, it rises to the highest point within the radiator, which is the top section. This trapped air acts as a barrier, preventing hot water from fully circulating, leaving the top cold while the bottom remains hot.
The most effective way to deal with trapped air is to bleed the radiator. You’ll need a radiator bleed key to do this. With the heating turned off, place a cloth or small container beneath the bleed valve to catch any water. Slowly turn the valve until you hear a hissing sound, that’s the air escaping. Once water begins to flow steadily, close the valve. After bleeding, check your boiler pressure, as releasing air can sometimes lower it.
Sludge or Corrosion Inside the Radiator
If bleeding doesn’t resolve the problem, internal sludge could be the cause. Sludge is a thick, dark mixture of rust, dirt, and limescale that forms when metal inside the system corrodes and particles settle at the bottom. While sludge tends to collect at the base, it can also build up in certain areas, disrupting water flow and creating cold patches in unexpected places. This issue can worsen over time, leading to reduced heating efficiency and even damaging the boiler.
Removing sludge requires a professional power flush, where high-pressure water mixed with cleaning chemicals is pumped through the system to break up and remove the build-up. This is a specialist job, and it’s best carried out by experienced heating engineers in Bedford or Milton Keynes who can ensure the system is cleaned thoroughly without causing leaks or damage.
Heating System Imbalance
If you notice that some radiators heat up very quickly while others lag, your system may be out of balance. This happens when the flow of hot water is uneven across the heating network, often because the lockshield valves, which control water flow, aren’t correctly adjusted. Without balance, radiators closer to the boiler can take most of the heat, leaving those further away cooler.
Balancing involves making careful adjustments to the lockshield valves on each radiator to control the flow rate and ensure heat is distributed evenly. While this can be done yourself with patience and a thermometer, it’s often quicker and more accurate to have a heating engineer perform the balancing, especially if you have a large system.
Low Boiler Pressure
Boiler pressure plays a crucial role in moving hot water through your heating system. If the pressure drops too low, the reduced flow rate can prevent radiators from heating fully, and the top sections are often the first to be affected. Low pressure may be caused by small leaks, recent bleeding of radiators, or problems with the boiler’s pressure vessel.
First, check your boiler’s pressure gauge. Most systems should read between 1 and 1.5 bar when cold. If the pressure is low, you can top it up using the filling loop according to the manufacturer’s instructions. However, if the pressure keeps dropping, it’s important to have a heating engineer investigate, as this can be a sign of a hidden leak or a faulty boiler component.
Preventing the Problem
The most reliable way to prevent uneven heating is through regular boiler servicing. Annual checks allow engineers to remove trapped air, detect and clear sludge early, maintain correct pressure, and balance the system if needed. This helps ensure your heating runs efficiently and avoids unnecessary breakdowns.
Boiler and Radiator Support in Bedford and Milton Keynes
FixBot provides radiator repairs, boiler installations, servicing, and maintenance for homes in Bedford and Milton Keynes. Our experienced heating engineers can identify the cause of uneven radiator heating and resolve it efficiently. Call us on 01234 815101 or complete our contact form to arrange a service.
