Worcester Heatslave 20/25 oil boiler expansion vessel

[Terrywookfit]

The only problem doing tis is , a blocked communication hose or pipe will give the same symptoms and the only way to ensure they are not blocked is to do it with the vessel connected and make sure the water from the vessel is expelled

If the hose is blocked then removing vessel will mean boiler pressure gauge does not drop to zero.
Surely if you removed E/V and system pressure stayed at whatever !!! Alarm bells would tinkle !!

 

[ianmcd]

Trust me , you can drain the system pressure and the pressure guage can go to zero , then disconnect the expansion vessel communication and if that had a blockage you wont do it again

 

[Burnerman]

That's interesting? I assumed that there was a "rubber ball" inside the vessel, with a Schrader valve attached to it (like a bike inner tube, all in one piece), so the only possible way you could get water out of the Schrader valve would be if the "ball" was punctured somewhere. The existing expansion vessel is welded, so there's no possibility of taking it apart to inspect the "ball".

That’s always been my understanding too - if there’s water at the schrader valve, surely the diaphragm is passing?
John

 

[ianmcd]

That’s always been my understanding too - if there’s water at the schrader valve, surely the diaphragm is passing?
John

Nope

 

[Burnerman]

Would you mind explaining, Ian? Where’s the water coming from (unless the diaphragms do let some water through?)
Thanks
John

 

[Avocet]

Would you mind explaining, Ian? Where’s the water coming from (unless the diaphragms do let some water through?)
Thanks
John

Yes, I'd be keen to know more too! Are there any cutaway drawings of the innards of an expansion vessel that you could post up, please?

 

[Terrywookfit]

Trust me , you can drain the system pressure and the pressure guage can go to zero , then disconnect the expansion vessel communication and if that had a blockage you wont do it again

Obviously if you disconnect without thought you will fook up.

My method especially on the Worser Green star 1 which kinks the hose for fookin fun!! Is to sit the vessel over a large 25 l bucket (Which I use for Turbolator cleaning) I then Crack the nut open and gently wiggle the flexy until water starts to drip and gradually undo it depending on flow and pressure gauge reading. PRV is always available if needed. I carry spares so no worries.
I have never been sprayed by sludge or water yet .The hose is left dripping into the bucket whilst I deal with the vessel. Which is left off until the last to preserve the flexy

 

[Terrywookfit]

Yes, I'd be keen to know more too! Are there any cutaway drawings of the innards of an expansion vessel that you could post up, please?

Condensation on the metal.

 

[Avocet]

Condensation on the metal.

There's a lot of it! I could easily get a pint out - probably a lot more!

 

[Terrywookfit]

Recharge it properly and leave for an hour. Then check pressure again.

 

[Avocet]

I found this online. That's more or less what I thought would be in there, except I thought the air would be in the bladder and the water would be in the tank. Actually, they seem to work the other way round, with the water in the bladder and the air in the tank. Either way, the two are supposed to be separate, so I shouldn't be getting water out of the schrader valve.

 

[Burnerman]

I guess it all depends on the permeability of the diaphragm membrane, Avo.....whatever it’s made of.
My own Heatslave (12/14, 1999) gave me an eyeful of rusty water when I pressed the schrader and there was rust and streaking around the seam so out it went. The airside chamber was full of water but I’ve no idea how long it had been there.
Anyway, I pressurised the new one and connected it up - assuming the diaphragm was in the lowest position so there would be minimum air on the water side.
Since then I’ve replaced the flexy connection pipe and the pressure gauge which had blocked.
I suppose we should really repressurise with nitrogen but that’s hardly feasible.
John

 

[Avocet]

I'll maybe try cutting it open afterwards, to see whether the bladder has burst or not. It's had a good innings! My main problem though, is the fact that it's an obsolete part and the one that is supposedly the replacement for it, doesn't fit in the bleedin' boiler! I am, however, encouraged that the expansion vessel can be sited anywhere in the system and that there's no problem with having a hole in the boiler casing for the pipe to pass through. My only other alternative would be to try and find another pressure vessel of a different design that DOES fit - but it might mean going down to 10 litres. I'm not sure that would be sufficient.

 

[oilhead]

There are 2 designs of expansion vessels, one for primary heating water, as in your worcester, and one for potable hot water, as comes out of your taps.
The diagram you have posted is the latter, and the bladder is held into the vessel by a flange. Water expands into the bladder.
On your boiler, you just have a diaphragm held in the welded seam. One side is air, the other water. If you get a stream ofwater out of the schrader valve, then the diaphragm is split. It is rusty because i thas always been in contact with steel.

 

[Avocet]

There are 2 designs of expansion vessels, one for primary heating water, as in your worcester, and one for potable hot water, as comes out of your taps.
The diagram you have posted is the latter, and the bladder is held into the vessel by a flange. Water expands into the bladder.
On your boiler, you just have a diaphragm held in the welded seam. One side is air, the other water. If you get a stream ofwater out of the schrader valve, then the diaphragm is split. It is rusty because i thas always been in contact with steel.

Thanks. That makes perfect sense to me. Like you, I'm pretty certain that the flexible element (be it a bladder or a diaphragm) has failed. I can't quite picture how they would trap a diaphragm into a welded seam though. In fact, I'm curious as to how on earth they do any welding on the vessel without knackering the flexible bits inside! However, that's just curiosity.