Cold spots on radiators are one of the most well known problems of the heating system. They can be random spots across the radiator or it could be that the bottom of the radiator is cold and the top is hot or that the top is cold and the bottom is hot. It is important to know how to treat this problem to prevent paying more costly bills and to prevent future problems.
If your radiator is hot at the bottom and cold only at the top then the solution is quite simple, the radiator needs bleeding to release the excess air in the radiator. Radiators should be bled until all of the air has escaped and a drop of water comes out. This ensures water is right to the top of the radiator which is now fully utilised and will heat across its entire surface.
However, if it is the bottom or middle of your radiator that is cold and the top is hot, then the solution is not as simple. This problem indicates that your heating system may be clogged with a thick black sludge scale. No matter how high you turn the thermostat or how long you have the heating on, the cold spot will remain cold and your heating bills will be much more costly as the rest of the radiator is working harder to heat up this thick sludge.
One solution for the cold spots is the use of chemicals. Using a non acidic cleaner added via the expansion tank whilst the radiators are on should break down sludge and scale in the radiator. If after one hour of cleaning the radiator still has the cold spot, then it may be necessary to use more cleaning chemicals. When the cleaning has finished, drain the radiators and flush out the debris. This may need to be repeated if there is a lot of sludge in your radiators.
After this, adding a central heating protector eliminates corrosion and eradicates the chance of thick black sludge; it is therefore a good preventative measure for eliminating future cold spots on the radiator once your radiator has been cleaned and flushed of all debris.