Hot water heating systems need a little maintenance, like venting the radiators and draining the boiler, to keep things running efficiently. Gravity and hot water furnaces are not often installed in new homes today, but similar systems with the old cast-iron radiators throughout the house were fixtures in homes built around 1900, and some of them are still working. Clanking, popping, and gurgling as they swing into action whenever the thermostat detects room temperatures dropping, they provide a relatively steady flow of heat without the drafts you get in forced-air furnaces.

Hot water systems are closed, meaning that the water constantly circulates through the pipes and into the boiler. Newer units have many zones with two water pipes linked to each zone: one circulating heated water to the rooms and the other returning the much cooler water back to the boiler to get reheated. In the older one-pipe series systems, hot water flowed from room to room, and then back again to the boiler in the same pipe. The last room on the circuit never got as warm as the first.

To maintain a system, you should lubricate the circulating pump motor. Use a lightweight oil such as 3-in-1, and pour it in the oil cup.

In the fall and throughout the heating season, you also need to vent or purge radiators that don’t have an automatic purge system. To vent the radiator and drain the boiler, follow these directions:

  1. Open the valves on radiators and convectors to let out air.


  2. Close the valve.

    Don’t forget to drain the boiler to get rid of rust and mineral deposits. Read the manufacturer’s instructions, and then follow these steps:

  3. Turn off the power and water.

    Instead of the old cast-iron radiators, today’s units have free-standing or baseboard convectors. They’re less bulky, more efficient, and look much nicer than their ancestors and they provide the same amount of heat to all the rooms. The disadvantage of hydronic or hot water heat is that, because there is no duct work, you can’t have central air.

  4. Stick the end of a garden hose into the boiler drain cock.

  5. Open the vent valves on a radiator located on the top floor of your house.


  6. Turn on the water supply valve so fresh water will flush through the system.


  7. When the water stops running, close the drain cock and vents.

    Even though they’re closed, the water will continue flowing into the boiler and through the system.

Systems with a pressure regulating valve automatically turn off the water when the boiler is full. With other systems, you must watch the pressure gauge. Refer to the owner’s manual to find out what level is recommended by the manufacturer, and then let out the air in each convector, if needed, until the pressure is at the operating level.