A room will not warm up
Work outward from the heat source. Each step names the observation that sends you to the next one.
- Is the radiator or register warm at all?
If it is cold across its whole face, the problem is delivery, not the room. Check the valve head and pin, or the register damper, before anything else.
Why radiators heat unevenly - Is it warm at the top only, or the bottom only?
A cold top band is trapped gas. A cold bottom band is settled sludge. These are different faults with different remedies.
Why radiators heat unevenly - Do the rooms nearest the plant run hot while this one never arrives?
That is a distribution problem across the whole system, corrected by balancing rather than by anything done in this room.
Balancing forced-air registers - Does the room behave differently with the door open?
In a ducted system that indicates the return path is blocked when the door is shut, so the supply cannot get in.
Balancing forced-air registers - Is the heat arriving but not staying?
Now it is an envelope question. Check the junctions at floor and ceiling and the openings before adding more heat.
Where air leaks hide in an old house