Slow heating radiators

Matt C

I have two radiators in my hot water system that are always slow to heat. They are fed from the same 1" lateral. All other radiators in the system work fine.

Just upstream of the radiators, the 1" lateral comes off of a 2-1/2" main. Also at this location, another, 2", lateral comes off the same 2-1/2" main. The 2" lateral services 6 or 7 radiators, all of which work well.

The circulation pump is attached to the return piping on my system.

I notice that hot water seems to get to the 2 problem radiators fairly quickly, but does not cycle through the radiators until long after the other radiators are hot and the furnace cycle kicks off.

Could it be that the 1" lateral feeding the 2 radiators is undersized for this location? Without too much destruction I could change the lateral to 1-1/4 or 1-1/2. Would balancing the rest of the system help? And if so do I just close off valves at the other radiators to adjust the flow?

Sorry for the long question(s), hope to get some help as this has frustrated me for a while!

Mark W

Can't hurt

to throttle down the radiators that are working well.

Not enough details, and I'm just guessing, but it sounds as if your system may have orginally been a coal fired gravity system, and when the boiler was replaced and the circulator added it turned the system into a 2 pipe, direct return system.

Oh such a joy to balance, but it can be done. Mess around with the valves, if it doesn't work you can always turn them back to their orginal positions. Be gentle, I wouldn't force anything. Sometimes leaks around the stem/packing nut can be taken care of with a gentle tightening of the packing nut, but it wouldn't hurt to have some packing string on hand just in case.