Water – Is 68F too low for hot water heating thermostat? Final radiators not getting heat

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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?

Thanks

Update: picture of the boiler gauge:
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Best Answer

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.

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