Air and yet more air...

[sjashford]

I have a big problem of air (or some other gas?) in the central heating.
Need to vent radiators every day. Noise of bubbles moving around in the pipes all the time.

A bit of history:

• Problem started after the system was cleansed with an acidic cleaner (Fernox DS40)

• Has been drained, flushed and "neutralised" several times since

• New boiler installed (partly for other reasons). Also pump and main pipework replaced

Air/gas doesn't appear to be hydrogen (very small pop at start of venting, then nothing for the rest).
Cannot find anywhere it might be being sucked in - most of the system looks to be under pressure even with pump running (e.g. all radiators will vent not suck). Feed from header tank is on a single combined pipe.

No plumber I've spoken to can suggest anything (other than guesswork - gets expensive aftera while).

Any geniuses here got an idea...?

 

[Nige F]

Nowhere near a genius......and many other posters will agree but 4 wot it`s worth.is the boiler a low water content replacing a high water content ...I don`t like single combined pipes for feeds from header...separate feed and vent into a Myson airjec, or other dearator. That`s all. Br..a..i..n T..ir..ed Pump fitted wrong way round....has been known

 

[kevplumb]

read this

 

[sjashford]

OK, Some more info:
Old boiler was a Baxi (Bermuda?) back boiler
New is a Potterton Suprima 40L
Not sure about water content - both similar heat output so may be about the same?
It is a small system (5 radiators) in a top floor flat with header tank in loft
(just above ceiling level).
The original problem (with old back boiler) was excessive "kettling" noise, did not respond to mild cleansing hence use of acid cleaner (which still didn't have any effect).
Something odd I noticed before the first cleansing attempt: a load of fluffy white mouldy stuff floating on the header tank which I skimmed off before draining; and a load of slightly sticky black gunk at the bottom of the tank (about 1in depth) which I cleaned out after draining but I guess some of it might have made it's way down into the system.
Maybe some sort of bacteria in there?

Thanks in advance for any ideas...

 

[Nige F]

.
Something odd I noticed before the first cleansing attempt: a load of fluffy white mouldy stuff floating on the header tank which I skimmed off before draining;

...............Possibly old fernox solution not mixed properly......or body fluid from a dodgy plumber and a load of slightly sticky black gunk at the bottom of the tank (about 1in depth) which I cleaned out after draining............That is BAD.....could be corrosion from the system , deposited there by the water circulating through the vent.......yet another badly designed system,,Yet it`s not rocket science Not a boiler expert but pretty sure it`s lowwer water content...Needs looking @ by someone of equal brainpower to mine.....perhaps 35 years experience helps too

MOD

edited to correct quote

 

[ollski]

leak in the pump valve on the negative pressure side is a pretty tricky one to spot, my guess would be though that your rads are corroded...one they get to a stage even powerflushing is limited in its success. Also was the fresh water inhibited?, complete waste of time cleaning it all out otherwise. Don't forget that every time you bleed the air you are adding fresh oxygenated water into the system.

 

[Nige F]

Rather than re piping it properly.which it probably needs ..consider converting it to a sealed system, then it`s filled from the mains,and the air is blown out at the first filling,susequently any dissolved comes out and can be vented thru rads..........I wanna tell you a story...did a little job the other day, water had been making trickling/ gurgling noises in a large system for months.....under bedroom floor .. Myson airjec had been fitted but wrong orientation.....changed it and altered a couple of pipes...quiet as a mouse now.............as the old boy who taught me said" "There`s them as Know, and them as don`t and them as Never Will"

 

[sjashford]

Thanks for the advice.

In fact another plumber did suggest the conversion to sealed system, but for some reason I wasn't convinced. Being paranoid I worry that the increased presure might cause a big leak somewhere in the (possibly-dodgy) pipework; or alternatively that the air problem would still persist but cause over-pressure within the system...

I had considered raising the header tank as a way to increase system pressure and reduce suction points. Could probably get another 1.5 metres height on it. Plausible? Or complete waste of time...?

 

[DP]

Old boiler was a Bermuda, which (often) is fitted as a gravity system. The pump almost always is on the return. All works well until the boiler is replaced and converted to a fully pumped system. The pump gets moved and motorised valves are fitted. In all this exitement, the DIYer/ plumber forgets the three tee rule and pumpover results

Has been drained, flushed and "neutralised" several times since.

How did you manage this when the DS40 container comes with one packet only? I take it you did not dump the DS40 down the drain before adding neutraliser? The neutraliser is there to adjust the pH of the dumping water to make it safe for the drain

 

[ollski]

Old boiler was a Bermuda, which (often) is fitted as a gravity system. The pump almost always is on the return. All works well until the boiler is replaced and converted to a fully pumped system. The pump gets moved and motorised valves are fitted. In all this exitement, the DIYer/ plumber forgets the three tee rule and pumpover results

Struggling to pump over with a combined feed and vent though

 

[ChrisR]

We've read here of systems pulling air from gawd knows where, and long efforts to rectify. Moral of stories is to go to a sealed system. One didn't stop pulling air in until system pressure was 1.4 bar, then it did.
I'd go sealed, if still airy at 1 bar, add leak sealer and try at higher pressure, say 2 bar for a while.
Pipes don't leak just because they're Old. Rad valves can seep and rusty rads will fail sooner rather than later, but nothing you shouldn't be leaving anyway.

 

[sjashford]

Thanks again for all the responses - especially on a bank holiday!

Looks like sealed system is the best bet.

I guess this is probably not a DIY job...?

 

[ChrisR]

No reason why you couldn't diy.

You'd need a pressure vessel, say 12 litres. This can go in the airing cupd on the old feed pipe.
You need a pressure releif valve, which has a pipe going through the wall, a guage, and a filling loop between mains and the system somewhere where you can see the guage.
They will work anywhere on the system but there are some trad reasons for putting them on the return pipe.
You can buy kits from plumbers merchants.

Poke around a few sites like BES, plumbworld etc