22. Cold spots in radiator?

Experienced technicians will agree: only seldom is the cause in the radiator itself. Usually too little flow or insufficient water temperature cause the difficulties. Possible causes are:

• The system is not in balance.
• The conveying height of the circulation pump is too low or the pump is running at too low a power setting, which causes the flow-rate in certain circuits to be too small.
• There is too much air in the system.
• The thermostat control is covered by an item of furniture, curtains, etc. which is causing the temperature at the thermostat to be significantly higher than in the room itself, which in turn causes the valve to be completely or partially closed and the flow-rate will be decreased.
• The thermostat control is not being used correctly.
• The main thermostat is being subjected to large external sources of heat such as the sun's rays. Since the main thermostat has reached the desired temperature, the radiators in other rooms do not heat up.
• The water temperature is too low.
• The radiator is too long: if both the inflow and outflow connections are at the same end, the water might not be flowing through the entire radiator. For long radiators the connections should be at opposite corners.
• Impurities in the valve unit: when the system is filled, suspended particles can collect at the valve and decrease the flow significantly.
• The radiator is only partially warm: a phenomenon which is sometimes easy to explain. When the desired room temperature is reached, the valve will close even if the radiator is not yet completely filled.