Air building up in Central Heating system

Tucker

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 as the majority of the new plastic pipe is accessible under the upstairs flooring bar one or two areas. I've checked what I can see and it's fine and there are no signs of water loss where it's plasterboarded over.

I heard that plastic pipe can draw air in? I used barrier pipe and all the fittings etc matched the pipe manufacturers.

Any thoughts??

roger196

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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. Rad hot at top but cool at bottom is a sign of sludge build up. When you cleaned the system did you connect a hose to the system to pressure clean it or did you just drain it. Sounds like you just dislodged sludge which has appeared at this rad. Easiest way to clean is to remove rad and flush thru with hose in garden.


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. . Normally the bleed valve on the pump ( in the centre at the end of the pump shaft) is closed after the air is removed. Also there is usually an automatic air vent ( bleed valve) somewhere on the boiler. This has a small black cap the size of a car tyre valve which is usually left open. Most important to check manufacturers instructions first.

Tucker

Thanks.

I'll check the manual.

I drained it. Then isolated the boiler return, attached hose to a downstairs drain to release water, closed all but one rad at a time and used the filling point on the boiler flush each rad through until it ran clear and repeated for each rad.

Tucker

The manual says the valve on the pump is opened and left opened. It doesn't confirm it should be closed at any point. Mind it's been like that for 3 years and didn't have the air issue prior to recently adding to the system.

One thing the manual does say is after filling the system should be run to max temp, then emptied out. Refilled and run to max temp again to allow the vent to release any air and then rads bled.

Since I refilled, it's not been on beyond half way, so perhaps I ought to do that procedure to purge it as recommended and then run it and test.

roger196

Tucker wrote: »

I drained it. Then isolated the boiler return, attached hose to a downstairs drain to release water, closed all but one rad at a time and used the filling point on the boiler flush each rad through until it ran clear and repeated for each rad.

This normally works fine if you attach one hose to the flow and another to the return at the boiler, or attach hoses to either side of the pump valves ( external pump, you will need to make up some one and a half BSP adaptors) or attach hoses to the flow and return of a removed radiator. Somehow I think you have managed to leave a loop somewhere for the sludge to remain. Another possibility is there is a branch in the flow pipes allowing the pressured water to find an easier route than the sludged one. These are quite common in bungalows. Sometimes the system will be designed for two zones which has the same effect.

Tucker

Yes, looks like it's not been flushed well enough.

Once it's warmed up, I'll drop the water out and do it again. The fact the water is murky says it's not all been cleaned out as well as I had thought.

I'm praying there's no small leak in the roof of my extension causing it, as it's all skimmed now!
I checked the pipework under pressure beforehand, but then had to screw a further 25mm insulation to the underside of the rafters and then the plasterboard. I marked out where the pipes ran and made sure I stayed well clear with the screws, but you start to doubt it when somethings suggesting a possible leak!

It might not show so quick as it's behind the insulation and foil backed board......

roger196

Tucker wrote: »

It might not show so quick as it's behind the insulation and foil backed board......

Get a cheap damp meter form B&Q or www.screwfix.com about £20. Use this to detect early stages of leaks. A pressured system will have a pressure gauge which can be monitored. Remember the pressure rises when the temperature rises so compare at the same temperature each time.
Are you able to isolate flow and return pipes to the extension as this will highlight if the problem is there or elsewhere.

Tucker

Thanks for the thoughts.

I used the superseal inserts with every pushfit joint and I tested all the joints before any were boarded over, so I think I can rule out those. Most of what I've done is accessible via the upstairs floor and I've checked all of it and it's fine.

I could quite easily replace the 2 old radiators, which would mean they are all recent.

qoute: fresh water is oxygenated, gradually released and eventually bled out

That might well be the issue. In the past, I've only ever drained the upstairs and isolated other areas. The air was bled out on refilling and then I repeated it after running the system for a few days and that was enough to remove it all.

This was the first time I've emptied the whole lot and increased it in size with new additions. Whilst I refilled and bled the system, I am wondering if all the air bubbles and bits of air that entered when refilling in full, our in fact slowly finding their way to the highest rad and over time it will all come out and setle down?? Would it seem probable that it could take 5 or 6 extra mini bleeds to remove all the air?

I've monitored the system pressure on the boiler. It's only dropped a tad once or twice after I've bled this rad of the air (max of 0.1 bar and not every time), which would seem logical regardless of whether any water is escaping, as the released air will impact on the pressure?? It's certainly not losing water at any pace, which would be aparent by now.

I can access the pipes where I've branched them off to the extension, so in essence, I could isolate it with some modification. such as stop taps on both, which might be worth doing in any event, but would require me draining the upstairs, so might be something to add when I do a further flush through.

roger196

Tucker wrote: »

. such as stop taps on both, .

make sure these allow uninterupted flow when on, usually use isolation valves rather than gate valves

makemdano

Had a similar problem which was down to sludge. End 2 rads in system not working probably. Tried pressurising boiler to relief valve but rads still only had pressure on one side. Water was BLACK

Plumber suggested powerflush but didn't have equipment, checked qaround and was quoted £500+
Managed to hire one from HISS from around £80 and it worked a treat, system is now fully opertional, house is warm and pressure maintained. There's lots of info on google about how to do and the HISS instruction was good. Just need to have basic plumbing skills (need to isolate the combi). I can't recommend this highly enough.

Apparantly the sludge in my system was settling and sealing pipes. When system was charged from filler loop, it reached optimum pressure but the sludge had caused an airlock. Overnight the sludge moved thus lowering the pressure again.

The only alternative to this powerflush was to rip up flooring to examine pipework internals. All of this started when I knocked 2 rooms into one, had a new kitchen installed so the system was of for about 6 weeks, apparantly causing the sediment settlement.