Now I have to bleed the towel rail.....

[mjnelson]

Hello again,

Right, I have a GlowWorm 18sxi condensing boiler, pressurised system, 7 radiators and a towel rail (the top of which is the highest point of the system). About a month ago, we had our boiler serviced by GlowWorm and they drained the system and reressurised the expansion vessel. At the same time we added an inhibitor to the system.

The system now holds pressure brilliantly, but every week I need to bleed the towel rail - something I never had to do before. Strangely, it's as if for the first 5 days of the week the top rail is red hot, and then days 6 and 7 air fills the top rail (as if it's not steady, it's a sudden change.....maybe I'm wrong though, since it's subjective).

When I bleed the air out, the system pressure hardly changes and I haven't had to top up yet. It takes approx. 2 seconds to bleed it.

So.....is this kinda normal, having added inhibitor? Could it be due to repressurising the expansion vessel? Is it just because the system was drained and refilled? Just seems weird that this happens now

Thanks for any wise words,

Matt

 

[wingcoax]

I'm not a plumber but it sounds like the service caused a leak and you should get the firm back to cure it.

 

[Hugh Jaleak]

Possible for the small amount of air you describe, there is still some trapped in the system, its slowly making its way to the high point. Only when its had 4-5 days to build up before its noticeable. Or possibly a slight leak somewhere, water is not escaping but slight amount of air drawn in.

 

[mickyg]

I haven't had to top up yet.t

there's no leak. just a bit of air in the system. What inhibitor did you add and how much? I've known inhibitors to bubble a little for a short time if its overdosed.

 

[mjnelson]

Thanks for the replies. MickyG - I used HPS's General Heating Inhibitor - 500ml bottle and i added the lot. Perhaps Fernox would have been a better purchase?

 

[Diyisfun]

Had my system flushed 2 weeks ago & re fernoxed.
I am bleeding 2 rads daily, I was told it my take a week to get all the air out. Im amazed at the amount of air, considering its such a small system (7 rads)

 

[mjnelson]

Well.....it's now a good couple of months later, and I'm still getting air in the top rung of my towel rail.

I'm bleeding it every couple of weeks.

I have gone over the whole system and not found any leaks whatsoever.

The top rung will remain red hot for several days, and then quite quickly go progressively cooler.

So.....what's the deal? Is it still just air "in" the system and I need to keep bleeding and eventually it'll all disappear (since it was totally drained and then refilled), is it related to pump speed (not aware that this was altered during the boiler service), is it related to boiler temperature (it's currently about halfway)? Something that I have noticed is that the rads seem very, very hot - but I may just be becoming almost paranoid about anything central-heating related

I'm really struggling with the notion that I never ever had to bleed this towel rad, and now, purely after having an expansion vessel refilled + inhibitor added to the system, I have a noticeable build-up of air every few weeks, but absolutely no signs of any leaks (not even 'ickle ones).

I have even put a balloon over the pressure relief pipe's end, to see if anything is dripping (no signs at all) and even wondered if it could be "sucking" air in here, but.....

Also, as a side-note, I have an auto-air vent in my airing cupboard, near the filling loop....red cap.....should this be loose, tight, in-between?

Thanks ever so much for any useful info,

Matt

 

[Adrian80]

This site may be handy

http://www.fernox.com/?cccpage=air_in_CHS&sub=3

if it is gassing i dont think holding a match to lots of venting hydrogen is a good idea!

I would suggest collecting a bit in a upturned test tube (cup or something) and then lighting it.

Hydrogen gives a very characteristic squeak when lit in this fashion.

I have two towel rails, and tall column radiator, i also bleed a fair bit of air every couple of weeks.

The CH pipes are all new, absolutely no leaks, the system was tested for a month with all the boards up. I think the micro leak is probably the cause, i think it will be most likely on the radiators valves.

Strangely i had trouble sealing the rad valves on all the column / towel radiators. I think the reason was it only had 1 cm of thread for the valve to go into the radiator, whereas a normal rad has 2 or 3 cm of thread, which imo is likely to make a much better seal if jointing tape is used.

just my thoughts.

 

[mjnelson]

Cheers for the reply - I've stumbled across that fernox site before.....in fact, that's what made me thoroughly check for leaks (when hot and cold) even though nothing (apparently) had changed with the rest of my system.

D'oh! It's so frustrating!

 

[stiler]

If you are sure there are no leaks then it does sound like you still have some containments in the system. You could try fitting one of these
http://www.nlbengineering.co.uk/ £5 from PTS
They obviously don't solve the question as to why it's happening but it does deal with the end result.

 

[mjnelson]

Nice one, thanks for that. I thought the old Aladdin autovents were a bit ugly, but these ones look fine - even for the top of a towel rail.

My only reservation with fitting one of these is....well, I will lose any idea of how much air is (potentially) building up. At least at the moment I know that a rung's worth of air is present after a couple of weeks. Man, it'd be great if I bled it tonight and it never returned.....and I knew it was all ok..... :-S

Maybe a rung's worth of air every few weeks is still just the air that was present in the whole system when filled from empty? Perhaps this much air spread around all the rads wouldn't seem so odd - but since I have TRVs on most of the others, I don't really notice whether they are continually red hot at the top.....(if that makes sense).....so I only notice when it works its way to the top of the towel rail.....?!

Matt

 

[mjnelson]

Thought: could a microleak on the pressure relief valve cause air to be drawn in? I'm pretty sure that during the boiler service last year the engineer "cleaned and refitted" it - no real noticeable water is leaking from it, but...