Air in Baseboard Radiators

stonebm

Hi There- I posted this in Fine Homebuilding's Breaktime and was referred over to here. Hope someone has some good advice...

This winter I noticed a faint noise from the baseboard heat in our house (gas-fired boiler with two zones- one for upstairs and one for downstairs). I suspected air in the lines so I bled them out. I've done this quite a bit since we moved in because we've rearranged the locations of the baseboards to facilitate a kitchen remodel. Sure enough, there was air in the pipes. After bleeding the pipes, the faint noise was gone but now when the heat kicks on, I hear water gurgling through the pipes. Again, I figure there's still air in the system so I bleed it again but it doesn't seem to improve the situation. The gugrling goes away about 10 minutes after the heat comes on but the initial noise is pretty anoying.

I've repeated this procedure probably a dozen times over the last week to no avail. I've not noticed any leaks in the system either. Everytime I open the spigots to bleed the system, there's a lot of air. I guess my question is this: is there something basic I should be checking on the system that may be malfunctioning and allowing air into the pipes? Since we've lived in this house, I've completely drained the system and refilled it several times and have never had this much trouble with air in the lines. The system is set up with an automatic fill valve from the city water supply if that makes any difference. I'd appreciate any suggestions. Thanks.

Big Ed

Test

Shut off the auto feed valve and take note of the boiler pressure. If the pressure drops then you have a leak .My first suspect would be a leak under a slab floor if I'am rebleeding a system over and over .With a leak, air can be pulled into the heating system when the circulator runs.

What type of radiation in your home? The kitchen was redone ?

Bill Nye

Do You

Do you have an automatic air eliminator, hy-vent ? Is it open ? Where is you circualor located in relationship to thew expansion tank? What is your static fill pressure? Do you have a fast fill lever on your auto-feeder?

All of the fresh water you introduce when you purge or refill your system has dissolved oxygen in it . If you really want to solve this problem you may need to do some repiping.

Check this book in books and more. http://www.heatinghelp.com/shopcart/product.cfm?category=2-16

stonebm

Thanks for the replies. Both pumps are on the infeed side of the boiler. There is an expansion tank on the outfeed side. It has one of those gadgets that's supposed to let air bleed out of the system (looks like a pill bottle- sorry don't know the name of this thing). I've not tried shutting off the fill valve and monitoring boiler pressure but will try that. The fill valve does have a fast fill position but it is not currently in that position.

The house has fintube radiation everywhere except the kitchen, which now has a kickspace heater. The kitchen previously had fintubes with cabinets built over them (real butcher job). The kickspace heater has been in operation for two years with no problems. I've never had this much trouble with air in the system before (even after the kitchen work).

Couple of other things: I noticed last night that there is a wet area on the floor by the boiler near the pressure relief valve and the valve outlet seems to be wet. Could this be stuck open slightly and admitting air? I'm tempted to drain the system and replace that just to see. Also, we're noticing that the second floor is overheating (up to 80 last night with a set point of 73). The second floor recirc pump isn't running so I assume the thermostat is working correctly. I've also noticed that even with the 2nd floor pump off, the radiators are putting out a lot of residual heat. I'm wondering if there might be a connection between these symptons. Maybe a slug of air in the first floor loop that is redirecting hot water intended for the first floor into the second floor loop. Crazy thought? Thanks again for the suggestions.