Shower Water Hammer

[steveoelliott]

Hi Folks,

 

I have a shower with a Mira Minilte external mixer... When initially turning the tap on there is a horrendous and continuous "bang" "bang" "bang" and you can hear it in the pipes behind the tiles... Once you turn it a little further the banging stops.

 

I had our plumber take a look and his suggestion was to replace the shower mixer but before spending ~£200 on a new mixer plus fitting just wanted to see if there were other possibilities.

 

On a separate note, I do have what I would class as "normal" water hammer elsewhere in the house on occasion when a tap is shut off quickly / aggressively.

 

Thanks...

[PeterW]

So fit a hammer arrestor on the incoming cold water. A 2 litre potable expansion vessel is change of £30, it’s less than an hour to fit. 
 

What water pressure do you have incoming to the house as whilst you’re cutting into cold supplies, a variable pressure reducer would also help somewhat and you can set it so you can retain a decent pressure. 
 

£100 should get you sorted and stop the problems across the house. 

[steveoelliott]

Thanks Peter...

 

So is that vessel a hammer arrestor in and of itself? or is something else needed in combination. Most of the specific hammer arrestors I have seen are for individual appliances rather than for the whole house but that would certainly be more practical. Do you need one on the hot water too? I have a megaflow system.

[PeterW]

No - your water hammer is because there is no expansion anywhere in the system. What I would also have checked (first...) is that the Megaflo expansion tank is at 3 bar. Very rare to get water hammer in a sealed system as there is usually a route to expansion somewhere. Has the tank and reducer been checked or serviced recently ..??

[steveoelliott]

Thanks Peter... that’s interesting actually as today I did some layman’s troubleshooting and if I run another hot tap in the house the problem is solved but if I just run a cold tap the problem still exists.

 

I asked plumber about servicing the mega flow when he did the boiler as it’s not been done since we’ve lived here ~2 years but he said he was worried as it hadn’t been done for awhile that it would leak after..

 

I have noticed also that when hot water is heating up that when opening the taps there is a sudden burst of pressure for a couple of seconds.
 

Are you a plumber by chance? 

Edited April 10, 2021 by steveoelliott

[PeterW]

Sounds like the bladder has perished on the expansion vessel. You can check it yourself if you have a tyre pressure gauge ..?

 

Top of the expansion vessel there will be a black cap - under it is a standard car tyre Schraeder valve. Just push the tyre pressure gauge onto the valve and read the pressure. It should be 3 Bar (pre-charge will be on the cylinder somewhere) and if it’s below that then get the foot pump out !! Don’t be tempted to run an air line to it - you’ll split the bladder ...
 

If it is zero then you may struggle to pump it up. Turn the water off at the mains, open a hot tap and then try again. 

[steveoelliott]

Thanks Peter. There is no visible expansion vessel on my system. I was told it’s all integral. 

[PeterW]

Eh..?? Is it a Megaflo cylinder then with that really nasty air space at the top ..??

 

wonder if the installer read this ..??

 

[steveoelliott]

This is it... 

[Nickfromwales]

If it’s a ‘bubble top’ cylinder ( which traps air in the upper 1/8th for expansion ) then all you do is completely drain the tank ( using a hose pipe to drain from the cylinder drain off cock, not by just opening the hot taps ) and then just refill the cylinder to replenish the bubble. Simple as.

 

The pipe coming out of the top just extends down inside the cylinder, referred to as a ‘dip pipe’, and that makes sure the air cannot come out with the flow of hot water. The cylinder type needs to be confirmed somehow of course, but if you had zero expansion you’d be seeing water discharged out of the pressure relief valve on every single reheat cycle. 

The higher discharge for a few seconds is usually just the volume of expansion giving up its stored energy, and then you drop back to direct mains whilst the taps are open. When shut again, the stored energy builds back up ( cold mains incoming potential ) to allow the same to occur again. That tells me that expansion is present, otherwise you wouldn’t have that notable higher initial discharge.

 

Having no water hammer on the hot fortifies that opinion, so I’d say you have an aggressive cold mains and that is being further exacerbated by poor mechanical fixing of the house cold water pipework.

Buy a 8L potable expansion vessel and install

it on the cold mains as close to the stopcock as possible. Do that first, before touching anything. To commission it you need to know the static cold pressure at the stopcock so you can set the 8L EV back charge pressure accordingly. 

[steveoelliott]

Thanks for this Nick.

 

I "do" have water hammer on the hot. I actually solved the issue with the shower banging when turning it on by opening up another hot tap elsewhere on the system. Also If i aggressively shut a hot tap off upstairs then I get water hammer... cold I do not.

 

Either way, I think i'll get the Megaflow looked at and also look at getting one of those expansion vessels on the cold main.

 

Finally, does water hammer actually cause any real issues besides the irritation factor? I've read that it can blow joints etc but then I know folks that have just lived with it for years without incident.

[Nickfromwales]

14 hours ago, steveoelliott said:

Thanks for this Nick.

 

I "do" have water hammer on the hot. I actually solved the issue with the shower banging when turning it on by opening up another hot tap elsewhere on the system. Also If i aggressively shut a hot tap off upstairs then I get water hammer... cold I do not.

 

Either way, I think i'll get the Megaflow looked at and also look at getting one of those expansion vessels on the cold main.

 

Finally, does water hammer actually cause any real issues besides the irritation factor? I've read that it can blow joints etc but then I know folks that have just lived with it for years without incident.

It can cause old joints to give up, but only in extreme situations really. The pipe is physically moving during generation of the hammer noise so it is something to address if possible.
The UVC is a cold mains dependant device so hot and cold are married, hence the issue sometimes resides on both supplies, but giving the system some expansion at source ( stopcock ) should wipe the issue out systemwide.

[steveoelliott]

Thanks Nick...

 

I take your point re securing the pipes and certainly something I'd look to have checked when refurbishing bathrooms etc in future. Just don't fancy smashing the tiles and ripping the plaster board off the wall to get to them

 

I think having a EV on the supply will be my first port of call... The arrestors I had seen prior to this discussion were just single appliance and not system wide.

 

 

[Nickfromwales]

I doubt if the offending pipes are in the bathroom, more like the long straight runs under the floors to get there. Usually it’s caused by the long runs between the joists which never get clipped in or are just rested on noggins, with the pipes free to bounce around a lot or just slide in one direction when the waters flowing and then ‘bang’ back to their original resting place when it stops ( hence the term “hammer” ). 

The noise may seem to come from the bathroom, but if you go elsewhere and ask someone to knock the tap on/off you’ll likely hear it further away.

The cheap / quick fix is to install the EV. 8L is a lot bigger than I anticipate you’d need, but to diagnose this remotely means I err on the side of caution. Plus, you can never have too much expansion only too little. The cost difference is a round of drinks, so better off do it once and go a little overboard.

[steveoelliott]

Thanks Nick... I'll give that a go out of interest.

 

Yes agree with you... Thanks for all your help.

[steveoelliott]

On 12/04/2021 at 11:00, Nickfromwales said:

I doubt if the offending pipes are in the bathroom, more like the long straight runs under the floors to get there. Usually it’s caused by the long runs between the joists which never get clipped in or are just rested on noggins, with the pipes free to bounce around a lot or just slide in one direction when the waters flowing and then ‘bang’ back to their original resting place when it stops ( hence the term “hammer” ). 

The noise may seem to come from the bathroom, but if you go elsewhere and ask someone to knock the tap on/off you’ll likely hear it further away.

The cheap / quick fix is to install the EV. 8L is a lot bigger than I anticipate you’d need, but to diagnose this remotely means I err on the side of caution. Plus, you can never have too much expansion only too little. The cost difference is a round of drinks, so better off do it once and go a little overboard.

 

Coming back to this after some time... I have been advised today by my plumber that as my Megaflo doesn't have a balanced cold supply (we inherited this system), we can't install the 8L expansion vessel.

[Nickfromwales]

1 hour ago, steveoelliott said:

 

Coming back to this after some time... I have been advised today by my plumber that as my Megaflo doesn't have a balanced cold supply (we inherited this system), we can't install the 8L expansion vessel.

Sounds like a lame response without a solution  

To ‘balance’ the system retrospectively requires two things. 
1) add a secondary pressure reducing valve at the cold mains stopcock. 
2) fit a 22mm non return ( single check ) valve on the hot water outlet of the UVC. 
That’s what he should have said to you…….and then he could happily have fitted the chuffing EV to resolve all issues in one morning. 

[steveoelliott]

19 minutes ago, Nickfromwales said:

Sounds like a lame response without a solution  

To ‘balance’ the system retrospectively requires two things. 
1) add a secondary pressure reducing valve at the cold mains stopcock. 
2) fit a 22mm non return ( single check ) valve on the hot water outlet of the UVC. 
That’s what he should have said to you…….and then he could happily have fitted the chuffing EV to resolve all issues in one morning. 

 

Thank you... what is the need / purpose of both of these when there isn't a balanced cold supply. Just so I can steer them

[steveoelliott]

I presume the additional secondary PRV is to make sure that both the pressure of source for cold into supply and into the cylinder are the same; thus both hot and cold same pressure. What does the non return valve on the hot water outlet?

[Nickfromwales]

16 hours ago, steveoelliott said:

I presume the additional secondary PRV is to make sure that both the pressure of source for cold into supply and into the cylinder are the same; thus both hot and cold same pressure

Exacta-mundo, squire. Both PRedV's need to be the same bar value ( eg 3bar a piece / 3.5bar a piece etc ).

16 hours ago, steveoelliott said:

What does the non return valve on the hot water outlet.....do?

That makes a retrospectively balanced UVC installation G3 compliant by preventing back-pressurisation of the cylinder in the event of the secondary PRedV ever failing. A lot of plumbers don't have much of a clue of these solutions and just read instruction books on the day. If it doesn't look like the instructions, then it's an automatic 'fail'....  There's always a solution, you just have to get off your arse and go look for it.   

Edited June 10, 2021 by Nickfromwales

[steveoelliott]

1 hour ago, Nickfromwales said:

Exacta-mundo, squire. Both PRedV's need to be the same bar value ( eg 3bar a piece / 3.5bar a piece etc ).

That makes a retrospectively balanced UVC installation G3 compliant by preventing back-pressurisation of the cylinder in the event of the secondary PRedV ever failing. A lot of plumbers don't have much of a clue of these solutions and just read instruction books on the day. If it doesn't look like the instructions, then it's an automatic 'fail'....  There's always a solution, you just have to get off your arse and go look for it.   

Thank you...

 

Well for now, i'll leave the EV... Sounds like I need to first find a plumber who really understands unvented and G3 beyond the text book.

Edited June 10, 2021 by steveoelliott

[Nickfromwales]

For completeness, on a previous project, the above information was sense checked with Telford UK, which I then executed. Subsequently, I then employed one of Telford's appointed G3 representatives to inspect and commission for G3 sign  off, which was instantly granted upon inspection and with flying colours.

Edited June 10, 2021 by Nickfromwales

[steveoelliott]

The plumber has now installed a white Zilmet 18L potable EV on the cold inlet to the Megaflow having deduced that the internal baffle on the cyclinder had broken down. This has reduced significantly the water hammer on the hot to the point that unless I shut off the taps like a "ninja" there is no hammer and even then less than before.

 

One thing I have noticed and will question him on when he returns is the noise that comes from the EV. When the cyclinder is heating you can hear sounds that I can only describe as similar to a whoopee cushion or squeaking. Should the EV be silent in operation or is some noise expected?

 

Edited June 17, 2021 by steveoelliott

[Nickfromwales]

12 minutes ago, steveoelliott said:

having deduced that the internal baffle on the cyclinder had broken down

Explain more please. Baffle? Where?

[steveoelliott]

5 minutes ago, Nickfromwales said:

Explain more please. Baffle? Where?

Sorry, so the Megaflow HE has an internal expansion baffle / vessel. It is apparently common for these to breakdown.