Home>Discussions>PLUMBING>Radiator needs constant rebleed.
2 posts / 0 new
Last post
Radiator needs constant rebleed.

We have an oil-fired water baseboard heating system. We have 2 zones, one for the 1st floor and most of the basement and one for the second floor. We have one pipe from the furnace that supplies hot water to the second floor. From this single pipe each radiator has a supply line and a return line. My problem is on the last radiator in the chain. This radiator needs bleeding (ie. removal of air) at least once per week. Anyone have an idea why this is happening? Also what do we have to do to fix it?

Re: Radiator needs constant rebleed.

This could be hard to find and remedy.

It's normal for any air that gets into the system to always migrate to the highest point in the system----since the problem rad is on the 2nd floor, it's a good probability that this is why that particular rad is getting the air.

There are several ways air can get into the system----if any water has been added recently by opening the water inlet valve near the boiler (house water supply water) there would be some ENTRAINED AIR (which is always present in new water) that eventually separates from the new water as it is pumped thru the system---this will of course eventually find its way to the highest point.

Sometimes there is a small leak somewhere in the piping system (loose bleed valve, small leak in the piping) this will cause a loss of water, then a replenish reaction from the automatic refill valve (if the refill valve is on automatic), then a separation of air & water in the piping, then excess air in the problem rad----check the system for any leaks---sometimes the leak is hidden behind inaccessible walls---but do a thorough search to see if you can find anything & repair any found leaks.

Also check the pressure/altitude gauge on the boiler; the system should read 12 psi (per square inch) water pressure when the system is cold (not firing), and approx 20-25 psi when the system is heating/firing----if the system reads below 12 psi when cold, add some water by opening the water inlet valve & watch the gauge till it gets to 12 psi----a low psi reading may allow additional air to circulate in the piping if you have an older type expansion tank (long 3' steel tank propped above the boiler system).

Check the air scoop/automatic bleeed valve assembly on the horizontal stretch of the main supply pipe (large pipe 3/4' or 1 1/2" to 2" pipe) near the boiler, there's usually a finger-tightened screw at the top of this air scoop/bleed valve that often clogs with crud---loosen & clean the top screw till you get air/water out of it.

If your 2nd floor rad happens to be more than 28' above the boiler (measure with a steel rule from the building exterior if necessary, or estimate) water in the piping may not be able to get up to the problem rad---thus, add more water to the boiler until the cold pressure reading on the boiler gauge is 15 psi (2.31 X 15 = 34')/(2.31 X 12=27.72').

Another possibility is that many HW boiler systems are piped with the circulator (pump) on the main RETURN piping near the boiler (especially very large, old, heavy circulators); this forces the piping water to be pumped INTO or toward the expansion tank, which can cause a negative pressure in the near-boiler pipes---this will often cause any near-boiler air eliminating valves to suck in some air whenever the boiler/circulator pump comes on when the system calls for heat---if this is found to be the problem, the remedy is to probably forget about it & live with the problem, or else go thru the expense it will cost to reposition the expansion tank or circulator so that the circ is PUMPING AWAY from the expansion tank; consider this possible cause LAST on your list of things to try to get the air out----it is much easier, less expensive & less intrusive to the system to try all the other mentioned possibilities before thinking about moving around circulators or expansion tanks.

For more info consult the sites below.


Sponsored Stories

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.