OSO unvented cylinder, air gap.

[krnlg]

Hi,

I have an OSO Direct 20 RD unvented cylinder and am trying to recharge the air gap.
I know this is a simple procedure but I've followed the instructions and am starting to think either I'm doing something stupid or my lowest hot tap is not low enough.
I'll try to explain, bear with me!

Untitled

• krnlg
• 4 Feb 2012
• 1

I've numbered everything so that you can tell me if I'm opening the wrong valves etc. as the instructions are very badly printed and it was difficult to read which valve was the commissioning cock, etc.

Following the instructions, I turn off the mains valve and turn on the hot tap.
Then I open valve (1) which I believe is the commissioning cock.
Then I hold open valve (2) and lots of water flows, gradually decreasing.

The instructions say to keep going 'until water flow stops from the commissioning cock'. The problem is, I can stand there for probably almost an hour holding the bloody valve and water still comes out, gradually slower and slower. I did also try holding valve (3) open because I thought I might have the wrong valve. I hope that didn't cause any problems?

Anyway, within a few weeks the air gap has gone again (discharge from tundish when heating, drop in hot water pressure)

Because I've tried this a few times now with no lasting success, the last time I did it I figured I'd follow the commissioning instruction of filling the cylinder until water comes out of the commissioning cock, figuring that the amount of air inside the cylinder at that point would have to be correct. So, after holding valve (2) for some time until only very very slow drips came out of valve (1) and hardly anything from the hot tap, I turned on the mains valve and slowly filled the tank.
Water started dribbling slightly from valve (1) but I kept going until there was a sudden increase, then I closed the valve and let it all fill up normally.

My question is:
1. Did I do anything stupid?
2. Should I have just closed (1) as soon as ANY water came out?
or 3. Should I try draining from valve (4) which is nearer the bottom of the tank?
The lowest hot water tap is about half way between the heights of valve (1) and (4) on my photo.

Sorry for such an overly detailed post but this cylinder is really irritating me and I want to get it sorted. I had the EXACT same problem with the same model of cylinder at my previous flat and never got it sorted. This should not be a difficult procedure after all!

Cheers for any help!

Josh

 

[oldbuffer]

I've had this problem with these cylinders. Usually down to the commissioning cock being jammed, so that although you open it, little or no water comes out. This results in the cylinder not clearing down sufficiently for the air gap to be re-established.

Solution is to turn off cold feed to cylinder, remove hot water outlet at top, and drain entire cylinder by syphoning though hot water outlet hole. Takes ages.

When empty, remove and replace commissioning tap. There is a downward pipe inside the cylinder from the commissioning cock, so be absolutely sure the tank is empty to below that level before removing. Can't remember the size buts its standard and you can get it from any decent plumbers merchant.

Then reconnect hot outlet, commission per instructions.

Don't forget these are meant to be serviced annually by someone with a "G3" ticket. None of the above has anything to do with the safety aspects of the cylinder.

 

[gasbanni]

For speed .water off .all hot taps open .drain from both drain offs at once.

Using gaffer tape and a weight at the end hold the blow off open ( I use a perfectly sized pair of stillsons which under their own weight keep it open)

when drained fit two new drain off washers to the drain offs fill with commissioning cock open every thing else closed.
When water comes out of commisiong cock hose pipe close it .....done ............

Turn power off to the elements whilst doing this !