air building up in CH

[tucker]

Hi

I recently added a downstairs extension and in the process extended the central heating loop to add a new rad. I also changed a single for a double.

Prior to adding the rad I ran the system with some sentinal x4000 for 2 weeks to remove and sludge and then cleaned out the system, added inhibitor and re filled it. All the new pipework was exposed for several weeks, so I could check for leaks and all seemed well.

I've changed all but two of the rads over time now and those two are about 17 years old.

These two rads seemed fine, but over the past two months, one seems to be getting a build up of air and the other has gone cool at the botom. Both are upstairs.

I've bled the one with air about 5 times and over a 10 day period or so it has a little air in it again and the top isn't as hot as the bottom. I've also noticed the water is murky, despite me emptying it and flushing it out?

Boiler is a saunier duval Thermaclassic F30E combi and it's a closed system. The pump has a bleed valve on top which I've checked and it's open.

Any idea why I'm getting air? I've no obvious signs of any leak and can't see why any small amount of air isn't venting via the bleed on the pump.

Would replacing the two old rads be worth considering or have I not flushed it properly?

 

[newbie1]

you will never fully de sludge a system just by adding a cleaner
powerflush is the only way
did a system sunday and that took eight hours and had to clean the magnet after every rad and still didnt get it all out

 

[Cds]

This could be a few things:

1) System leak although this would seem unlikely as you have already checked.

2) When you bleed the radiators is the boiler/system running. You should always bleed systems when off. It is possible to draw air into a system fro the negative side of the pump.

3) The air could be gas (hydrogen) which is being generated as a by product of corrosion.

Air/gas will rise to the higher points of a system and thus not vent from the vent on the pump.

I would consider have the system power flushed or at least fit a Magnaclean and add a system cleaner (run the system with the cleaner for 2 to 3 weeks and clean the Magnaclean every day to start with). Corrosion often takes place under a build up of sludge so it is a good idea to ensure all of this has been removed.

 

[tucker]

Thanks for the thoughts.

I've bled it with system off, although rad was still hot.

I looked at the magnaclean while I was doing the extension and the problem was locating it. My boiler is in the kitchen and the flow and return go straight up into the ceiling with no room for one above it. Beyong that the pipework is amongst the joists, so I couldn't see where I could put one. Can I fit one horizontal?

It sounds like I could do with a proper flush out. The odd thing was this wasn't happening beforehand and it ought to be cleaner now that before?