Water Cylinder noise issue

malexicon

Hi there... first post on a forum so excuse me if I am a bit long winded here.. I have an issue with my unvented indirect water cylinder. It is heated by a Worcester 24i system boiler and is a newish is Gledhill 150L tank installed Feb 2021. There is an issue that seems to occur, on a semi regular basis when the cylinder is heating - there is a single banging noise that occurs, usually (but not always) around 2 to 3 mins before the cycle is due to end, and sometimes the same time frame after the cylinder has stopped. I only noticed this a few months back after we changed the timings of the hot water after it was switched off when we had some work done (replacing an ensuite shower room and replacing a radiator with a towel rail - no major reconstruction was undertaken in this though). There is no loud bang noise when the central heating is on (usual clunks etc when heating / cooling) so this appears to be an issue with the cylinder - I have noticed though that if the CH and HW are on at the same time all the water from the boiler goes to the CH so I have separated the times from each other - this seemed to help a little. So far I've have BG up twice and Dyno on their plumbing side who have changed a valve (this is definately the right way round) / checked this and that and see no issues. I also had a plumber stop by who checked the expansion vessel was pressurised and had a chat about it - he suggested that the noise might be a build up of pressure or something when heating. 

The cylinder is due its (first) annual service in a couple of weeks - any ideas? I am not a plumber or gas engineer, and the noise is loud and disconcerting when it occurs so would like it sorted if I can. The flow in has a red handwheel gate valve located as it travels up the pipe to the inlet - Flow in to the cylinder seems slow, (it tinkles in) but again I dont know whats normal. Return pipe has another handwheel type valve after it. There is no auto bypass type valve. 

I wondered if the issue could be these handwheel valves not being open enough (or too much?) or that there might be air getting in somewhere, for example from the pump which is integrated into the boiler? Other that that I am pretty much baffled? I know that the boiler also has an integrated bypass valve in it? Might there be some kind of issue with this as it nears the cycle end / start. 

Any ideas gratefully received. Naturally I am not a G3 plumber and wont be making any changes myself but would be good to have some more ideas to discuss when the service takes place to see if this can be fixed..

Thanks

Bendy_House

malexicon said:

Hi there... first post on a forum so excuse me if I am a bit long winded here.. I have an issue with my unvented indirect water cylinder. It is heated by a Worcester 24i system boiler and is a newish is Gledhill 150L tank installed Feb 2021. There is an issue that seems to occur, on a semi regular basis when the cylinder is heating - there is a single banging noise that occurs, usually (but not always) around 2 to 3 mins before the cycle is due to end, and sometimes the same time frame after the cylinder has stopped. I only noticed this a few months back after we changed the timings of the hot water after it was switched off when we had some work done (replacing an ensuite shower room and replacing a radiator with a towel rail - no major reconstruction was undertaken in this though). There is no loud bang noise when the central heating is on (usual clunks etc when heating / cooling) so this appears to be an issue with the cylinder - I have noticed though that if the CH and HW are on at the same time all the water from the boiler goes to the CH so I have separated the times from each other - this seemed to help a little. So far I've have BG up twice and Dyno on their plumbing side who have changed a valve (this is definately the right way round) / checked this and that and see no issues. I also had a plumber stop by who checked the expansion vessel was pressurised and had a chat about it - he suggested that the noise might be a build up of pressure or something when heating. 

The cylinder is due its (first) annual service in a couple of weeks - any ideas? I am not a plumber or gas engineer, and the noise is loud and disconcerting when it occurs so would like it sorted if I can. The flow in has a red handwheel gate valve located as it travels up the pipe to the inlet - Flow in to the cylinder seems slow, (it tinkles in) but again I dont know whats normal. Return pipe has another handwheel type valve after it. There is no auto bypass type valve. 

I wondered if the issue could be these handwheel valves not being open enough (or too much?) or that there might be air getting in somewhere, for example from the pump which is integrated into the boiler? Other that that I am pretty much baffled? I know that the boiler also has an integrated bypass valve in it? Might there be some kind of issue with this as it nears the cycle end / start. 

Any ideas gratefully received. Naturally I am not a G3 plumber and wont be making any changes myself but would be good to have some more ideas to discuss when the service takes place to see if this can be fixed..

Thanks

The sentence in bold is the stand-out one, I think, and it's clear that's what your suspicion is too.

I, also am not G3, GS or now't, and you are right that you shouldn't touch any of this, but fully understand able that you want to explore possibilities as a few pros have looked at this and are seemingly scratching their heads.

'Bangs' from a boiler or its associated system are usually down to one of two things; One is overheated water in some part of the boiler (and it usually is in the boiler itself, and not outside of it - but the shock can travel), and the other is a sticking valve that releases suddenly.

For the first, the most common cause of overheating water is that it isn't being dispersed quickly enough by the 'pump' and valves. This can happen, for example, if a valve restricts flow before the boiler has disposed of the last bit of heated water. For instance, if a flow or diverter valve has closed, restricting flow, and the main exchanger in the boiler is still super-hot and then makes the surrounding water near-boil as it cannot escape. I guess it can also be caused by a faulty overheat 'stat inside the boiler, but this will usually be obvious on a more continuous basis. And a faulty by-pass valve (if an auto type is fitted) could also cause this.

For the sticking valve option, I guess this could be a diverter valve (as in a combi - which yours ain't) or perhaps an auto by-pass valve, but I don't know. 'Bangs' at/near the end of a cycle are usually caused by the first of these - the water flow from the boiler is somehow restricted after the boiler (and pump) has shut off, but it still has a hot exchanger in there trying to lose its heat to the water.

When you consider that a CH system has a much greater resistance to flow compared to a short coil in a DHW cylinder, it should seem obvious that - if left to their own devices - the DHW side would receive much more flow than the CH, hence the red-wheeled valves which are used to restrict the flow to the DHW so that the boiler can get a fair share. These, I guess, should be set to give an even-handed balance betwixt the two.

That's about all I can say, and none of it points to anything specific. I would suggest, tho', that in exactly the way that all your individual radiators are balanced to each other so's they all get roughly the same flow, the flow to the DHW cylinder should also be balanced to the CH system so it, too, gets a fair share. From what you describe, this does seem to be far less balanced than it should be.

But obviously no-one but a G3 will be touching this!

Q - can you recall times when both the CH and DHW were running at the same time, and the DHW was timed to go off before the CH? If so, any 'bangs'?

These red wheels - are they part of the cylinder? Ie, does the setup appear to have come pre-plumbed? Or are they obviously 'away' from the cylinder, so added separately by the installer? If the latter, I'd take a photo and send it to Gledhill and ask their advice. I'd do that anyway - tell them what's going on, describe your full system, and see if they have any ideas. Tell them your G3 is scratching his head...

malexicon

Hi there - thanks for coming back - you are right - my main suspicion here is around the flow and return somehow - I find it perplexing that the issue is not uniform - let say it happens in 25/30% of cylinder heating instances - which kind of made me wonder if this was an issue with the cylinder itself or the piperwork/boiler/pump - on balance perhaps its the later, but the noise is loud and 'plasticy/metalicy' which make me wonder if there was some kind of pressure forcing its way into the cylinder itself - its hard to trace where the noise is really coming from.

I am struggling a bit to recall when the system was running both CH and HW at the same time - I do think it was a bit worse then - which suggests perhaps not enough water getting into and out the flow and return to the cylinder (and ties with the issue with the CH taking all the water. I guess in this instance the motorised valve for the HW is open, but sitting there getting nothing but hot air. I also meant to say earlier than the cylinder stat is set to around 60 degrees or so (as is recommended) - but the cylinder never really seems to get there - it switches off when you click i manually etc - which again suggests that the flow in might nit be sufficient to heat to full temp - a modern UV cylinder should surely get up to full temp (at 60) by 30 mins or so. 

I run the HW in the morning for 45 mins and 30 mins later afternoon/early evening - morning seems to be worse for the banging, but in both instances, when it occurs its around switch off time.

The red wheels have always been there as far as I know. there is on one the flow pipe before it gets to the cylinder - the one on the return is after the drop back on the pipe as it (I assume?) returns back to the boiler.

Very much appreciate your helpful and considered reply.

Bendy_House

30-odd minutes should get an already 'nicely-warm' cylinder up to temp, yes, but not a cold one.

The reason I asked about whether the issue occurred when BOTH CH & DHW were on is that if the DHW was turned off before the CH, then I wouldn't expect the bang as the CH was nicely taking care of the boiler flow, so no issues.

Something you can try; with the DHW on for at least a half hour, turn the cylinder 'stat up and down and see where in the middle it 'clicks'. I'd hope this would be pretty close to the 60oC it's set at? If it's significantly below, then your cylinder would seem to be slow in heating up, which would - as you say - suggest a limited coil flow.

malexicon

That's an interesting thought about the CH/HW being on together - though it doesnt work back if my recollection is correct about how often this happened in the past when they were on together. I can see how the flow then fully moving to CH would work if the HW was getting flow at the same time, though this doesn't seem to be the case.

On the temp front again, its an interesting one. We dont use the full amount of hot water or anything like it as sometimes we shower at gym etc. The temp, today, was close to 60 when I clicked down, but the cylinder would have had, by my reckoning around 2 hours of being on (with no 'opposition' from the CH) by the end of this mornings cycle.

Would think, after reading your post again that this might be a limited flow in and then out of the coil. Though there was no significant work done as part of last years remodel (there was a new shower put in - sometimes we get a valve closing noise from that, but cant see how that is directly linked to the HW Cylinder as there is no direct correlation) I suppose the team who fitted it could have turned the red wheels, thus restricting flow. Would I be right in thinking that the pace of the flow of the return can only match that of the flow in given that its a pressurised system - provided of course - both the red wheelgates on the flow and return pipes are at the same level - I'll not even be touching these, best left to someone who knows what they are doing.

Hopefully the G3 plumber who'll be servicing will be able to decipher what I, along with your help, have come up with to make the right changes. BG have been ok - but you don't seem to get a gas service engineer who is also G3 anymore which is why Dyno came and, although they are sister companies, they dont seem to work together/share notes etc which is not great.

Thanks again.

Bendy_House

As you say, the 'system' water - what's in the boiler, the rads, and the cylinder's heating coil, the pump, the motorised valves, etc. - is completely separate from the actual DHW inside the cylinder wot comes out of your tap. They should have no effect on each other.

It's strange that there would be a red-wheeled valve on both the flow into and return out of the cylinder coil. What you do often get is a valve on the flow, and a second valve across the F&R to act as a by-pass; not a very sophisticated by-pass, but hey. So, are you certain that these two red-wheeled valves are on the pipes you say?

If they are, then - yes - the flow through the heating coil will be at the minimum set by the most closed of these valves. If either one is near fully closed, then opening the other one full should barely have any effect; the near-closed one will be doing the restricting. (Hence me wondering why there's two...)

Any chance of a nice wide photo to show the cylinder and all the 'bits' around it?

malexicon

I cant get it all in sensibly but here you go - the below is the return from the cylinder - here you can see the wheel valve close to this, but not directly on the pipe

malexicon

..and here is a pic of the wheel valve which is on the pipe itself that enters the flow on the cylinder... 

Rodders53

Bendy_House said:

30-odd minutes should get an already 'nicely-warm' cylinder up to temp, yes, but not a cold one.

A Gledhill 150 litres has a heat up time of 25 minutes according to the manufacturer  https://www.gledhill.net/uploads/Gledhill-StainlessLite-Installer-brochure-MARCH2019-v19.2-WEB.pdf  with the correct flow rate through the coil and heat input from the boiler.

I think we may need some pics of this plumbing install to attempt to understand the plumbing?  Especially these handwheel isolator / flow restriction valves?
Unusual to have  any such devices in most CH installs.

That BG plumbers have visited and declared all well seems odd, too.

malexicon

Thanks for this Rodders - please see pics above. 

The BG guys either cant see whats up or say its plumbing, the Dyno (BG) guys say its the boiler pressure or something else - to be a bit more fair to them allI could tell then was that there was banging from the cylinder - which of course didnt happen when they were there... I am probably a bit more informed now (hopefully) with more knowledge as to how the flow is going to CH (not HW) when on together and also that the heat up time is clearly slow - along with what appears to be a slower tinkling sound of the flow into the cylinder coil. Hope this helps - I think, though not sure that the plumbing (that is under the cylinder anyway and not directly attached to it) is the same as it has been since the house was built 20 odd years ago with the exception of a new valve installed on the motorised valve to the HW (changing this made no difference)

There are no gate wheels attached to the CH piping - this seems to run up, enter through the open motorised valve then head down the piping system with no real restraint. Heating comes on ok - heats up fine for a house with older radiators - any noise from CH is pretty much at heat up / cool down after it switches on and off so could be entirely down to this - there may be some air in the system as it sounds a little bit like a slap noise from time to time.

One other thing that did happen fairly recently was that we had an issue with mains water pressure due to a local blockage (a stone) in the stop as it enters the house under the sink - this was fixed - water pressure is much better now (though not outstanding) - might this be a factor? 

Boiler pressure hangs about one - just about in the green - its gets topped up from time to time.

Thanks again.

Bendy_House

Mains pressure doesn't affect the 'system' pressure - they are separated - and having it at ~1bar is ideal for most circumstances.

The needle doesn't flicker or move much as the system heats up?

The mains pressure could affect the stored hot water, but usually in the opposite way - ie if the mains pressure increased somewhat.