Bleed radiators, nothing happens

[Ollie24]

when i go to bleed the radiators in my house there is no hissing coming from some, the downstairs radiators bleed fine, the upstairs ones don't do anything when u turn the bleed screw, no water no hissing, the upstairs rads are all cold at the bottom, but the rads downstairs are all fine apart from one, it's all of the same central heating system so i'm lost. any help?

[alan30]

Are they upstairs ones switched on at the valves where the pipes go in and out? For water to get in and replace air the valves have to be open.

[jedimistress]

This happened to me recently. Have you checked the pressure on the boiler?

I checked mine and it was low, so I filled it using the fill valve. Next thing my dog comes running downstairs and there is a loud loud hissing sound. The water was flying across the room from the radiator.

Try adjusting the boiler pressure if you can, but don't unscrew the rad valve completely like I did first.

[stanleyman]

If you have a vented system with an expansion tank in the loft then probably the ball valve has stuck causing the system to run low on water. If it is a pressurised system then refill to one bar, vent the rads refilling as you go.

Switch off the system when you vent the rads as otherwise this can draw in air and compound the problem. Once all rads are free of air the system may need balancing to force water to rads that do not work well. Open up both valves full on the radiators furthest away from the boiler and close down the hottest radiator valves nearest, on the valve that needs a spanner. This will even up the flow through all rads.

[Ollie24]

Thanks for your replys, i checked the boiler pressure and it was a bit low so i have filled it up, so hopefully it will stay ok, so far so good, thanks for the help.