Bleeding radiator question

Is it a sealed system? Presumably it is.

NT

Air lock in the pipe feeding it? Shut down all other radiators to try and force the flow through the problem radiator.

r.

So - air comes out and then no water? There must be some presure pushing out the air - but the presure goes when the water level get to the valve? Very odd. Is the system pressurised properly? Water should piss out.Are both valves open (not necessarily fully)?

That air is probably the gas resulting from the products of oxidation (rust) inside the rad. There is obviously a blockage to both sides of the rad, or the water pressure is inadequate.

If you have a leak you can get negative pressure in the top of the house. So a hiss as a bit of air goes _in_ then no water comes out. TW

Sealed system or vented?

Are you sure that is not air being sucked in you can hear?

Sealed. The sytem is pressurised and heating all radiators, however, I increased the bar pressure and that appears to have sorted it. The bar pressure is now half bar more than it normally is.

ss snipped-for-privacy@hotmail.com wrote in news:u_eAE.390722$ snipped-for-privacy@fx31.am:

surprised the boiler didn't shut down due to low pressure.

Thats what baffled me as the boiler always run at a lower pressure so didnt feel the need to explore that avenue. Possibly the higher pressure has dislodged something or cured an airlock.

The only time the boiler has shut off was about 3 years back when it was almost at zero, had been away on hols and it wouldnt fire up on return, it will run ok at .25 bar and I generally take it up to 1 bar when necessary, on this ocassion I took it to 1.25 and it appeared to sort the issue.

Of course bar indications assume the dial is not faulty.

Remember that if its an upstairs rad, then the pressure at the RAD could easily be half a bar (i.e. 15' of head) lower than that seen at the boiler. Many boilers will work down to 0.5 bar, which could equate to no nett pressure at all on the first floor.

That could be it, the rad in question was on 1st floor.

surely on a sealed system, the pressure will be the same throughout the system.

If the pressure gauge is low down in the system it will "see" the weight of all the water in the system above it added to whatever pressure you have as a result of the compression of the gas in the expansion vessel.

For boilers installed in lofts, you get the opposite effect - the pressure shown on the gauge there will actually be lower than what you would measure on the ground floor.

You definitely need to keep it at a pressure where the highest point in the system is comfortably above atmospheric (comfortably, to allow for when completely cold or a slight leak) or air can get in and cause corrosion. As well as some radiators not using all their area.

:-)

Yup that's inflation for you, I think the accurate conversion is 33.46' now, but I was allowing for some wiggle room with my "~"

Thats what I thought after JR's reply but googling does say height gives a drop in pressure.

A non-pressurised system will be at atmospheric pressure at the highest point (header tank) and at atmospheric pressure plus the head of water at the lowest point.

A pressurised system is no different, except that its "atmospheric" pressure is higher.

SteveW

Well thast wot it meens innit - a wiggle symbol