I'm struggling to understand the interplay between the pump that pumps water and how the location of the feed expansion tank affects whether radiators work. In my system most of the radiators work okay, but he two on the second floor just below the feed expansion tank do not,I'm told that because there is not enough head/height difference between them. But the boiler has a pump that pumps the hot water around, and if you put liquid in a pipe it will just fill it so I don't understand the significance of the expansion tank ( I do get it for hot water system regarding showers).

Assuming it is issue is there way to get radiators on the 2nd floor working properly without investing in a sealed system. Could I install a second pump just to pump water to these two radiators ?

  • could the two rads on the second floor be vapor locked? Bleed the air off the top of those two radiators. That will help. – Paul Logan Dec 3 '17 at 7:09
  • I have tried bleeding, no air inside them – Paul Taylor Dec 3 '17 at 7:49

The open type expansion tank system fell out of favor, in my area, years ago. I haven't seen one of these beasts in 40+ years. The tanks were usually placed near the ceiling of the top floor and usually in a cupboard. They had a drain line that ran from near the top of the expansion tank to a basement drain. The heating system was manually filled from a valve in the basement which you would turn off when water appeared from the tank"s overflow drain line that you could observe from the fill valve area. At that point, the system was filled to it's normal operating height. If your tank is piped as I have described, you could add water until you see water coming out of the overflow pipe. then vent the radiators. As far as the difference between an open and a sealed system, a sealed tank would replace the open tank. Your system is OK and probably only needs to be filled. And get another service company for the bad advice regarding the height of the tank vs the radiators.

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  • I have since read that the feed/expansion tank does have to be above the radiators (which it is), but it doesn't say the greater the distance the better. But I guess the resistance to radiators higher in the house will be greater than radiators lower down, hence perhaps the system should be balanced in favour of radiators at top ? – Paul Taylor Dec 3 '17 at 20:18

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