Water Cylinder noise issue

malexicon

Grand thank you - I am hoping that it is making a bit of a difference already as the water (and air) whizzes round when the cylinder or heating is on - if not, and if the BG engineer gets called back I can ask him to have a look at that. Cheers again!

malexicon

Another update on this - tail end of last week we re-pressurised the boiler to around 1.0 cold - it has previously fallen to zero so this took a little while then I attempted to bleed the rads, unfortunately on some of them the entire fitting was moving so I couldn't do them all - but for the rest of them no air was expelled, just water. 

The re-pressurising of the boiler took away the air noise that was circulating with the water. I observed the pressure to see the effect of the bleeding and it did reduce slightly which I expected it to even through no air came out the radiators. 

On its next few runs the cylinder operated quietly, however a few mins into the cycle there was a rushing sound, a bit like flushing a toliet - the tundish was dry however and there were no drips from it. I have read elsewhere that these noises can be caused by air. Given that I figured that this would partly work its way out through the auto air valve as previously discussed, or further bleeding. I have not touched the bleed / drain valve that is on the flow pipe into the cylinder as I am a bit nervous about touching that one (and indeed don't know if I am allowed to?). 

Today on the second pass the flush noise appeared around 10 mins into the cycle (its appearance time had varied) bit sadly also we got a bit of a bang from the cylinder - as previously noted - not as violent as before but there never the less.

I had spotted on looking at the boiler pressure before this that the pressure had dropped a little after what had been a few runs of heating and water being on - perhaps thinking this was some air working its way out the system through the auto valve - so it will need topped up again next day or so and careful watching.

I think the core issue regarding no or much reduced water getting into the cylinder was the likely cause of the very loud previous banging - this has settled a bit and I was hopeful it might have gone completely until this evening. I do wonder if the 'flushing noise' is being partly driven by air which remains in the system / cylinder and that this might still be causing the cylinder to continue to make noise if its still preventing the water from fully doing its job, or, with the pressure now around 0.8 whether more water need to be introduced into the system to ensure there is enough flow going into the cylinder.

Any further thoughts would be appreciated on this. I think next course will be to re-pressurise again and see if I can get more air out somehow - I guess if the air is partly expelling itself then this process might go on for a few days - after that I'm not sure what to do as I dont understand the flushing noise, nor why I am still experiencing noise... back to BG/Dyno again probably unfortunately as clearly I cant do much more that I have.

Bendy_House

No air out the rads you tried. And you are hearing this air mainly around the hot cylinder?

Whatever air is in the system appears to be circulating mainly in the DHW loop, then, before it presumably finally gets expelled out an air vent, and results in a drop in system pressure. There's no water coming out the tundish, so presumably no water loss by that route. So the drop in pressure is either being caused by a leak elsewhere (but I don't think so, as it seems tied to the noise issue?) or is due to the air being expelled.

The only thing I can think of is the EV - the diaphragm is punctured, oozes out a stream of air into the system water, and the pressure then drops when that air is expelled.

That's all I can think of.

malexicon

Hi Bendy, that's for continuing to look at this. The rads click away on initial heating and cool down, I know this is normal but I expect it's probably not helped by whatever air is probably in the system. 

Like you, I considered a leak, but also think this is not likely. I take it you mean the EV bubble  that sits above the cylinder? Although I have not been directly in front of the cylinder when the flush noise happens (just heard it from an adjacent room) I think that if anything had been going out the tundish then there would at least have been some kind of residue still there. I dont recall the flushing noise at all before the bypass issue was sorted - would be EV be assisting here in removing air out?

I guess there's a case here for continuing to re-pressurise and bleed at least a couple of times more before I have to call back BG and ask them to check the expansion vessel etc and I am a good bit more informed (thank you again...) than I was when this whole thing started back in the autumn. For all I know (with the timings of the water previously coming on during the night) this has been going on since install.

It could be of course that the cylinder is a duffer... BG fitted as part of the Home are  agreement last year but who knows if they'd replace it again - problem being that so far they haven't been able to fix anything relating to this issue. The noise was worse when the bypass was 'stealing' the water, so it was almost as of the coil was kettling or something with a small amount of water, and probably very hot air, just going into it previously)

At the moment the flushing noise seems to be more consistent than the banging so if I can't get it to settle myself next couple of weeks and have to get them back out then they will be able to hear it. 

I know we touched on this previously but would I be correct again on saying that the new shower towel rail we put in last year couldn't be causing any of this? But as you said these are on totally different circuits from each other - I could see how this might bring some air into the wider system at install time, but not this...

Thanks again.

Bendy_House

No, for EV I mean the one on the boiler circuit, which maintains the system pressure - I imagine it's inside the BOILER casing. 
The other EV 'bubble' is - I think - to maintain a pressure reservoir in the hot cylinder, to help drive your hot taps, so completely separate. 
I can't see how the new towel rail could be causing this. It's pressurised to 1 bar-ish, so sir cannot/shouldn't get in.

malexicon

Thanks again. Like you - cant see how the new towel rail could have caused this and though my knowledge is very limited I cant see how a new shower, even if there was some kind of backflow type issue (highly unlikely as am certain there are check valves built into the new unit) would cause issues in the hot water cylinder. BG/Dyno are coming round on Thursday so will see what they say about it all - I'm not optimistic and in some respects wish they'd just tell me they'll replace the thing with a new (non Gledhill) one - but I imagine that will be down the line if it all. I will mention the EV when they are round, am hoping I get someone who knows the world of boilers and cylinders inside out this time to save me being passed around.

Bendy_House

Your DHW system is mains-pressurised (also called 'unvented'). This means that both your cold supply and hot supply are delivered at virtually identical pressures, driven by your mains. So no 'backflow' should be possible, even without check valves.

Bendy_House

Is this your boiler? https://www.worcester-bosch.ie/professional/products/boilers/greenstar-i-system-9kw-to-24kw

If so, look at the third pic on the first page showing the open casing - see the large flat silver cannister at the top-left? That's your EV.

IF that is your problem, then at least it looks quick and easy to replace.

coffeehound

My reason for asking for more photos was that there can be a situation where a section of cold pipework gets locked by the check valve and something downstream.  As the cold pipe warms up, it can become highly pressurised by 'hydraulic action'.  When the pressure does get relieved there might be a loud noise due to the pressure, but because it's only a small volume, it's a short sharp crack.  But, can't see anything and your plumber is happy with it so I drew a blank

malexicon

Hi there... thanks for both coming back. Re the boiler model...it is similar but an older version (no digital display etc) - so the expansion vessel looks a bit like a round red whoopie cushion as far as I can ascertain and is tucked away at the back of the boiler. I'll mention this when I speak to them Thursday. Pressure seems to have stabliised but I've not bled anything else out. Thanks for that re the shower - again, didn't see how it could be a problem. Although there is no 'balanced cold main' attachment to the cylinder there is a PRV under the sink on the incoming mains set at 3 bar anyway which matches settings on the cylinder.

Coffeehound - this, or something similar, still seems possible, I might have 'over positived' the comments from the plumber but he noted no issues with the install other than the issue with the bypass being fully opened.

My main questions on Thursday will surround the ongoing, but more tempered, banging - which may still relate back to some kind of air issue if its hanging around the DHW piping and the odd flush noise - I'll see where it goes this time - sadly I'm not optimistic at all. 

Thanks again.