I have a hot water heating system. It's a single loop in a ranch home. The ground floor is about 1500 square feet. When the oil furnace turns on, the first few radiators in the loop get warm, but the ending radiators barely get any heat. My thermostat is set to 68F.

If I push the heat up to 73F, then the ending radiators will get warm. I was thinking maybe there was some air trapped in the end radiators, but when I opened their bleed valve, nothing came out, not even water. This was while the hot water was circulating in the system.

I'm wondering if anyone has any ideas as to:

  1. Why the end radiator didn't spurt any water out when I opened the bleeder valve - could it just be jammed up, or is there not enough pressure in the system? My furnace says pressure is at 15 psi.

  2. Is 68F simply too low a temp to expect hot water to get to the final radiator?


Update: picture of the boiler gauge: enter image description here

  • Your wall/room/house thermostat setting is not the loop-water setting; depending on controls, your thermostat setting MAY or may not influence the loop water setting - more often not. What does the thermometer on your boiler (it's got water, it's a boiler, not a furnace) say?
    – Ecnerwal
    Feb 7, 2017 at 22:44
  • Looks like it's at ~110F, added a picture to the original post. I'm not sure if that's constant, or it 'll go higher when the boiler is running. I'll have to check back when it's running. Feb 7, 2017 at 23:14
  • Also follow up dumb question - there's a sticker on the boiler that says "thermostat should be set above room temperature" - isn't 68F room temp? Feb 7, 2017 at 23:17
  • Again, probably referring to the boiler's thermostat (setting the temperature of the water), not the one where you set the temperature you want the house to be. That's generally not something the average homeowner should be adjusting. Has this system been looked over by a pro in the past year or so? An annual tune-up visit is generally well worth the small investment.
    – Ecnerwal
    Feb 7, 2017 at 23:54

2 Answers 2


The pressure is too low. Normally when you bleed there should be air or water getting pushed out.

Find the intake valve and open it up a bit. Then go around and bleed the radiators and open the valve again for a bit. Repeat until all radiators spit out water when you crack open the bleed valve.

Then when the circulation pump kick in again it may push some air back into the radiator requiring another bleed. After that you should only need to bleed once a year or so.


Did you check the circulating pump to make sure it is working? Are the heating units radiators or baseboard units? Is it a series loop (one continuous loop of piping above the floor) or is the piping beneath the floor with each unit piped to the main pipe? If the piping is in the basement or under the floor you may have a monoflo system. Take a few pictures and post them so we can get a better idea of what is causing the problem

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