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Discuss Mystery water hammer in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

M

maw

Problem in video link
View: https://youtu.be/efrhhYhhquk


Does it when we turn bath taps on or shower either whilst the hot water is on or recently heated. I'm not 100% sure need to figure that out. Havent heard it do it with any other taps in the property.

We have an unvented hot water cylinder. Pipe that vibrates is the one coming from the white expansion vessel and you can visibly see it.

Specialist unvented company came to service it - no issues identified. Said it could be PRV but looked fine on inspection. 2 other plumbers also said prv. Took the expensive gamble seen as 3 people said the same thing, it hasnt worked. The guy checked the white vessel to see if it had blown it hadn't.

He now doesn't know what it could be so we are back at square one and with alot lighter pockets.

This info may help:

-Had a new washing machine recently, I switch the water valve and mains off and turned taps on. Still did it.

-dishwasher has broke. Stopping mid cycle. Turned the water valve off under the sink. Did it but to a lesser degree possibly because I'd done it 30 mins before. So could be coincidental.

-recently had boiler serviced. Engineer noticed it made a drilling noise whilst he was here and said that could be a problem. Then said it wasn't as he had something on low so could have been that. I asked if it did it again what could it be he said 1 of 4 things. If there is a faulty part in the boiler can a boiler cause this other vibration/noise? The boiler has done it again since so need it looked at anyway however could this explain the hammer or likely to be unrelated?

Anyone have any ideas from this information and video? Do I need a plumber, one with a g3 qualification or a heating engineer 😅 I'm desperate and worried no one will be able to fix it
 
SJB060685

SJB060685

The very problem myself and some associates have been discussing recently. Its caused by the sudden rush of flow when you open a hot outlet propelled by the charge of the diaphragm in the vessel. Clipping the pipe might help, the length of the expansion pipe can also affect it, although myself and my associates have agreed that really there should be something in line, next to the vessel to limit the sudden flow, without affecting the vessels ability to absorb the expansion. You want fast in and slow out.
Now, having said that you are NOT to do anything about this yourself. Approach a qualified G3 engineer and explain to him/her what ive said and take it from there. This problem can be cured but must be done by someone who's qualified and understands the implications.
 
OP
M

maw

The very problem myself and some associates have been discussing recently. Its caused by the sudden rush of flow when you open a hot outlet propelled by the charge of the diaphragm in the vessel. Clipping the pipe might help, the length of the expansion pipe can also affect it, although myself and my associates have agreed that really there should be something in line, next to the vessel to limit the sudden flow, without affecting the vessels ability to absorb the expansion. You want fast in and slow out.
Now, having said that you are NOT to do anything about this yourself. Approach a qualified G3 engineer and explain to him/her what ive said and take it from there. This problem can be cured but must be done by someone who's qualified and understands the implications.

Thank you don't worry i have no intention of touching anything myself. I have a g3 engineer coming out in a week and a half and will mention it to him 🙂 why would it suddenly start to happen after 4 years of no issue?
 
SJB060685

SJB060685

You mentioned you recently had some work done, does any of this work coincide with when the problem started? One of my associates suggested this can also be caused by an outlet drawing more hot water than can be supplied to the cylinder cold fill.
 
C

Chuck

Anyone have any ideas from this information and video?
Can you provide a couple of photographs of the pipework around the expansion tank please?

Has someone competent checked the expansion tank is sound and correctly charged?

If you stop the boiler from heating the unvented tank and let it cool down does the effect still occur with cold water? I think the answer is probably 'yes' based on what you've said already.

It doesn't sound like 'water hammer' to me. More like the sort of slip-stick friction you get when central heating pipes expand due to the passage of hot water. If I'm right, one possibility is the reduction of pressure due to opening the tap is causing the pipework to move. E.g. when you pressurise an elbow it straightens slightly and when you depressurise it returns to it's correct shape. This would be more plausible with plastic pipework than with copper.

If it is due to thermal expansion, it would explain your observation that once its happened, opening taps within 30 minutes results in less of an effect.
 
OP
M

maw

You mentioned you recently had some work done, does any of this work coincide with when the problem started? One of my associates suggested this can also be caused by an outlet drawing more hot water than can be supplied to the cylinder cold fill.

There are four things that happened prior to or around the time this new noise started appearing:

1) we got a new washing machine

2) dishwasher pump started failing now doesn't work at all

2) i actually forgot we had another awful vibrating noise from about June until October. I could never work out where it was from until I found a video of the noise. It wasn't every day but got alot more frequent. It happened between 3-5am and lasted several seconds. I found a video of the same noise.

View: https://youtu.be/zZg7MDp06dI
(not my video but this happened for shorter period of time)

I bled the radiators last month and found one which was full of air and the noise has not been back for a month since I did this.

3) boiler vibrated for the 1st time around the time this new mystery vibration noise started appearing. Again I don't have a video of it as it is completely random and very infrequent. It has done it now 3 times in two months or as far as I am aware. Had a boiler service 2 weeks ago everything seemed fine with it but it did make the noise. Engineer said it could be 1 of 4 things, tested it bit more and it didn't do it again. It has done it once since so going to get the heating engineer to have another look at it.

View: https://youtu.be/IUT8aNDXExs
again not my boiler but same thing. It has done it 3 times in 2 months and I'm at home all the time so unless it does it when I'm sleeping I'm confident its not frequent.

Does this give any more insight into the problem?

Are we just really unlucky to have separate issues or are they all somehow related?
Post automatically merged:

Can you provide a couple of photographs of the pipework around the expansion tank please?

Has someone competent checked the expansion tank is sound and correctly charged?

If you stop the boiler from heating the unvented tank and let it cool down does the effect still occur with cold water? I think the answer is probably 'yes' based on what you've said already.

It doesn't sound like 'water hammer' to me. More like the sort of slip-stick friction you get when central heating pipes expand due to the passage of hot water. If I'm right, one possibility is the reduction of pressure due to opening the tap is causing the pipework to move. E.g. when you pressurise an elbow it straightens slightly and when you depressurise it returns to it's correct shape. This would be more plausible with plastic pipework than with copper.

If it is due to thermal expansion, it would explain your observation that once its happened, opening taps within 30 minutes results in less of an effect.
Yes I got it all serviced last week by a company who only deals with unvented systems
Can you provide a couple of photographs of the pipework around the expansion tank please?

Has someone competent checked the expansion tank is sound and correctly charged?

If you stop the boiler from heating the unvented tank and let it cool down does the effect still occur with cold water? I think the answer is probably 'yes' based on what you've said already.

It doesn't sound like 'water hammer' to me. More like the sort of slip-stick friction you get when central heating pipes expand due to the passage of hot water. If I'm right, one possibility is the reduction of pressure due to opening the tap is causing the pipework to move. E.g. when you pressurise an elbow it straightens slightly and when you depressurise it returns to it's correct shape. This would be more plausible with plastic pipework than with copper.

If it is due to thermal expansion, it would explain your observation that once its happened, opening taps within 30 minutes results in less of an effect.
Yes it had a full service last week no issues found. Prv was replaced this week even though it looked fine - made no difference.

So I only heat my water twice a day morning and evening for a hour. It will do it regardless of whether it is heating up or has been off 5 hours. We don't notice the noise again after the first instance until the water has been heated in the evening. I tested it with the kitchen hot tap yesterday as normally it would be the bath or shower ran first so we thought it was only related to the bathroom. The noise occurred with the kitchen tap as well so seems like any hot water tap.

If it was a water hammer do they occur everytime a tap is opened or can it be infrequent? If it was to do with thermal expansion is this problem able to be fixed?

I've provided more info above about another two issues which could be related? One seemed to resolve when I bled the radiators. The other has occurred infrequently 3 times over the past 2 months.
Can you provide a couple of photographs of the pipework around the expansion tank please?

Has someone competent checked the expansion tank is sound and correctly charged?

If you stop the boiler from heating the unvented tank and let it cool down does the effect still occur with cold water? I think the answer is probably 'yes' based on what you've said already.

It doesn't sound like 'water hammer' to me. More like the sort of slip-stick friction you get when central heating pipes expand due to the passage of hot water. If I'm right, one possibility is the reduction of pressure due to opening the tap is causing the pipework to move. E.g. when you pressurise an elbow it straightens slightly and when you depressurise it returns to it's correct shape. This would be more plausible with plastic pipework than with copper.

If it is due to thermal expansion, it would explain your observation that once its happened, opening taps within 30 minutes results in less of an effect.
Yes specialist company dealing with unvented cylinders has serviced it last week. No issues identified. Replaced PRV even though no visible faults but didn't work.

Yes it will happen if the water is cold. I only heat twice a day for an hour atm. So if I turn tap on after its been heated but isn't actually on it will do it. After that it either won't do it or to a lesser degree more times than not I don't hear it again until I've heated the water for a 2nd time and then put the hot water tap on. I thought it was just the bathroom taps but its not as it did it with the kitchen hot water tap last night too.

I have added couple bits of extra info/videos about other issues that could be related in the post above. I'd actually forgotten about the noise earlier in the year as not heard it since I bled the radiators a month ago.
Post automatically merged:

After saying the boiler vibration was infrequent it just happened as we stood in the kitchen. Boiler had just fired up as the hot water programme had literally come on when it happened. The video doesn't show how loud it is and unfortunately only caught a little bit of it as it was over in seconds again. No fault code on the boiler. Vibration from white vessel occurred as normal when hot water tap turned on.
 

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