Problem with air in system

[MikeAustin]

I have just had some problems with my system fixed - and now I have different problems. When I bleed my radiators, they soon get air pockets in again. The fill pipe from my F&E tank also gets hot, so I think hot water is blowing back up it. When I bleed a radiator and go back to the fill, it is cool again.

I am confused for several reasons. How does air get into the system? Why does water expand up the fill pipe and not the expansion pipe? Should there be a NRV on the fill pipe at the tank?

 

[seco services]

check to see if the vent pipe is blocked.

what have you had done on the system ?

 

[MikeAustin]

check to see if the vent pipe is blocked.

How do I go about that? One general point that I don't understand is that the vent pipe is above the water level in the F&E tank, so it would require a higher pressure to get water into the F&E tank via the vent pipe than via the fill pipe. Should there be a non-return on the fill pipe?

what have you had done on the system ?

In a nutshell, I had a blocked system. It was flushed with FX2 and some minor pipework done to help the flow.

One peculiarity with my system is that the F&E connections are before the pump rather than after it. Does that make much difference?

 

[eeyore9]

There will more than likely be a blockage in the system most commonly where the first T is. ie if its a gravity fed sytem locate the DHW cylinder where the pump is there is an arrangement of pipes (flow and return) in to the bottom of the cylinder and 2/3rds up coming back out. get a magnet and place it on and around the copper pipes & on the brass fittings, if the magnet sticks to any area there will be magnatite(ironsludge)in that place.All you have to do then is drain the sytem, clean or replace the joints or powerflush the sytem!

 

[MikeAustin]

There will more than likely be a blockage in the system most commonly where the first T is. ie if its a gravity fed sytem locate the DHW cylinder where the pump is there is an arrangement of pipes (flow and return) in to the bottom of the cylinder and 2/3rds up coming back out. get a magnet and place it on and around the copper pipes & on the brass fittings, if the magnet sticks to any area there will be magnatite(ironsludge)in that place.All you have to do then is drain the sytem, clean or replace the joints or powerflush the sytem!

The system was flushed with FX2 only a few hours ago and the MagnaClean picked up a load of muck. Also, the problem I have is without running the HW circuit. The vent pipe is 22mm and vertical and the T joint has already been used to flush the system directly from the mains (i.e. with a flexible hose bridged to the mains supply).

 

[MikeAustin]

I have just had some problems with my system fixed - and now I have different problems. When I bleed my radiators, they soon get air pockets in again. The fill pipe from my F&E tank also gets hot, so I think hot water is blowing back up it. When I bleed a radiator and go back to the fill, it is cool again.

My installer (who just flushed the system and got it 'working' again) has just told me that sometimes one cannot stop pump over (I am running on position 2 of a Wilo Gold RS60). He suggests that I should convert from a vented system to a sealed system. I have heard they can be more problematic. What do you think?

 

[eeyore9]

The sytem must be flushed properly.I usually powerflush then take every rad off and use a hose to back flush the rads,once upright once upside down while tapping them with a rubber mallet along the top middle and bottom until no black water comes out. your system has been fushed so take off the smallest rad and try this if you still get dirt out of it its not been done properly (takes a day to flush properly).If theres dirt in rads you can guarantee that there is some in joints and connections in the sytem and as i said before a good indicator where is a magnet. p.s. i had one similar to your problem ie water coming back into cistern f&e(i could see bubbles) flushed system which made a big imrovement and also turned pump down as it was on full chat.

 

[MikeAustin]

... as i said before a good indicator where is a magnet.

I have been round the feed and vent pipes with a magnet but did not detect anything.

Untitled

• MikeAustin
• 29 Apr 2009
• 1

The flow seems to be good at the moment. It is air in the system that is the problem now. I don't know how it gets in. It seems to be generated in the rads. I get a nice torch-like flame when I hold a match to them during bleeding! Must be some FX2 still working in there.

p.s. i had one similar to your problem ie water coming back into cistern f&e(i could see bubbles) flushed system which made a big improvement and also turned pump down as it was on full chat.

I watched for some time but didn't see bubbles. Hot water backs up to the F&E via the feed. I turned the pump down to 2, and it is now on 1. The problem remains.

 

[JohnD]

It seems to be generated in the rads. I get a nice torch-like flame when I hold a match to them during bleeding!

What inhibitor was added to the system after the cleaner had been drained, rinsed and neutralised?

 

[MikeAustin]

It seems to be generated in the rads. I get a nice torch-like flame when I hold a match to them during bleeding!

What inhibitor was added to the system after the cleaner had been drained, rinsed and neutralised?

Fernox.

 

[JohnD]

but if it is still producing flammable gas, that will be a product of corrosion, so for some reason it is not working.

Maybe the cleaner was not drained and rinsed thoroughly, maybe the inhibitor was not mixed into the water into the rads, maybe it leaked out and was replaced with fresh airy water that allows corrosion, maybe it is pumping over badly in the F&E.

 

[MikeAustin]

but if it is still producing flammable gas, that will be a product of corrosion, so for some reason it is not working.

Doesn't this mean it is still working, but not finished? The corrosion is still releasing hydrogen from the acid.

Maybe the cleaner was not drained and rinsed thoroughly, maybe the inhibitor was not mixed into the water into the rads, maybe it leaked out and was replaced with fresh airy water that allows corrosion, maybe it is pumping over badly in the F&E.

I think all these may be going on, but the amount of air is so large that I wonder if something else is wrong as well. After only an hour or so, the rads can have up to 6" of air in.

 

[JohnD]

Doesn't this mean it is still working, but not finished? The corrosion is still releasing hydrogen from the acid.

all the acid should have been drained out, rinsed and neutralised at the end of the cleaning operation.

 

[MikeAustin]

Doesn't this mean it is still working, but not finished? The corrosion is still releasing hydrogen from the acid.

all the acid should have been drained out, rinsed and neutralised at the end of the cleaning operation.

Yes, it should have been. I suspect the installer drained the system down from the boiler - not from the lowest radiator drain point. He has done that before - and I emptied the lowest rad after he left. When he returned, he said it didn't matter. I need to watch him carefully! Seems like I should drain down the system properly and refill it myself.

 

[JohnD]

I'd give it a couple of drain/fill/run pump/drain cycles so you can feel confident it's all out.

some chemical makers offer a neutralising chemical after using their cleaner.

on final fill, use your inhibitor - will probably cost about £15 for a typical house.

Is yours an open system with a Feed & Expansion tank in the loft? If so, sponge it clean of any mud.