What happened to water and gravity?

[opps]

Hi all

I am posting this question because my little brain can't get around a recent experience where I removed radiator valves after draining down a system but still had water coming out of the rad tails.

Back story- two story house on a combi. The drain off point is about 2" of the floor near the combi. I attached a hose pipe, ran it over the back door threshold (about 2" off the floor) and let the hose run down the steps at the back of the house.

I opened all of the rad valves to max, opened all of the air bleed vents throughout the house. Waited a couple of hours and went to remove a ground floor rad. The guy laying the wooden flooring wanted me to remove the nuts and olives on the rad tails.

There was no more water coming out of the drain off hose pipe.

I started to undo what I assume is the nut for the flow side of the ground floor rad. Water started coming up. Worried that the water would run under the recently laid flooring I opted to go the the nearest rad, which is in the hallway (the hallway had generous gaps around the tails that would let the water run in to the cavity under the house). I undid the tail nut on the flow side and waited for another 10 mins or so.

Both tails are about 10 to 12cm higher than the highest point of the drain off hosepipe.

Why would the water not drain off to the lowest point? At one point I did try blowing in to the tail (of the rad I removed), it stopped the flow of water (tasted awful though) and then the water started to run over the top of the tail again.

 

[RandomGrinch]

I know to my cost, there can be a good few litres of water stuck in a combi behind an airlock!

 

[CBW]

Might have been a stub/leg of pipe perhaps in the system somewhere? You did drain the said rad didn’t you?

 

[opps]

Might have been a stub/leg of pipe perhaps in the system somewhere? You did drain the said rad didn’t you?

I drained the whole system (all of the rads), including the rad in question.

 

[BlueLoo]

Perhaps a vacuum further upstream is causing a syphon-lock?

 

[opps]

Perhaps a vacuum further upstream is causing a syphon-lock?

Perhaps, but I had previously removed each of the upstairs radiators so that I could paint behind them (both had . Admittedly, I only did a partial drain down. The only other rad that I had previously removed downstairs was a rad only drain as the tails could be pulled apart- meaning that I left the valves attached to the tails.