Why Would a Radiator Be Cold?

Written by david robinson
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Why Would a Radiator Be Cold?
Cold radiators may often be fixed without calling a plumber. (white radiator image by Ekaterina Sidorenko from Fotolia.com)

Radiators may fail to heat up for a number of reasons. Some problems are easily rectified by a competent do-it-yourselfer. Troubleshooting your own radiators saves you money and may reduce the time you must go without heat.

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The Pump

Radiators rely on an electric pump to force hot water around the heating system. If the pump isn't working the water will not flow and the radiators will be cold. If other radiators in the house are hot, the pump is working. If none of them are hot, the problem may be the pump or the boiler.

Air Locks

If air gets into the heating pipes, it travels around the system until it settles at the top of a radiator. If enough air is trapped in a radiator, it lowers the water level and only part of the radiator will heat up. If the radiator is hot at the bottom but cool at the top, you may open the bleed valve at the top of the radiator. Hissing indicates air is escaping. Close the valve when hissing has stopped.

Thermostat Settings

Some radiators are fitted with individual thermostatic valves. They override the main thermostat and switch on and off depending on the temperature around each radiator. If the thermostat is set too low or becomes stuck from a lack of maintenance, hot water won't enter the radiator. Turning the thermostat valve to a higher setting, or removing the top and depressing the pin a few times to loosen it, may restore the proper setting.

Valve Settings

To control the flow of water through a radiator there are often two valves attached to the feed pipes. One valve is at each end of the radiator. They are usually balanced to allow some water to enter the radiator and the rest to be piped past it. If the radiator is brand new, or has been serviced, these valves may have been turned off and not turned back on again.

Sludge Build Up

A black metallic sludge may form if the heating system has not been cleaned and serviced. It settles at the bottom of radiators, where the water flow is slowest. Radiators may be removed, taken outdoors, flushed with a garden hose and reconnected.

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