Re: Weird radiator filling - or rather non-filling

[charles]

an air lock in the sustem?

[Tim]

Hi everybody..

> A bit of a puzzler that I'm racking my brains over.... > > I'll set the scene: > My mums heating system (gravity fed with a header tank in the roof > space) has three or four rads upstairs , 3 normal and 1 slightly taller > towel rad in the bathroom not hugely taller , 4 ft perhaps? > > Anyway: It only gets hot at the bottom 1/3 - the usual problem you'd > think , bleed it ? > So I open the screw let out a tiny bit of pressurised air, heat rises a > bit up the rad (one bar) but no further air (or water) > > So I remove the complete nut that houses the bleed screw at top of rad, > No sign of water or air 'rush'? > > Soooo thinking laterally, I start to fill the rad with a kettle!, > several kettles and although the rad is now getting hot close to top , > the water never reaches to top of rad ??? > > and then I hear running water _outside_ the house, on inspection the > roof space overflow pipe is letting water out , if I stop with the > kettle filling the roofspace overflow eventually stops , so this is > kettle water leaving the building!! > > What's wrong ? > > and how the heck is the rad not filling up when the overflow is > obviously above the rad in question? > > >

Just a thought, we're you doing it with the pump running? Could I theory (depending on positioning) have been drawing water and air down into the rad with bleed valve open. Try again with pump off.

Tim

[Alan]

In message , Zaphod2 wrote

Airlock in the pipes supplying the radiator? Turn off all radiators except the one that has problems to force a water flow through the problem pipes.

[Zaphod2]

Thanks for the suggestions so far, I can't re-check any of it 'til next weekend , but will try the suggestions made.

The pump and boiler had almost certainly been running but idle when I first opened the bleed, but I did go and set the 'stat on cos I thought it might bring on some pressure to get some more air at the bleed but it didn't. The pump was running when I had the whole nut removed!.

And for information, the pump and boiler are on the ground floor , (this rad is upstairs).

Thanks in advance for any more ideas

I just don't understand how water can defy gravity and be pushed out in the roof space overflow rather than coming up to the top in the actual rad when it was open to the air ??

[Toby]

I think Tim has supplied the only plausible answer, that the pump was managing to suck water out of the radiator, so if you turn off the boiler (and wait until the pump stop if there is an over-run), then try bleeding the radiator (but don't just remove the bleed valve assembly and assume it won't gush!)

If this results in the radiator filling up, then that solves that question.

If this is the case, I would be mindful to check to see if the system is pumping over, and also if the expansion pipe that should be over the expansion tank is above the water line, or under the water (it should not be in the water, so should be above the overflow outlet).

Your filler valve should also be set to not fill the expansion tank to just under the overflow, and to keep a reasonable gap to allow for expansion (Mine is just over half full)