Water hammer/noise from pipework at night?

[Illuminate]

I attended a Job where the customers complained about noisy pipes more often late at night bur sometimes in the day. While I was there, there was no issue but the combi boiler was set to preheat and they said they usually put the washing machine on late at night.

With their permission I turned off preheat to the boiler and added a mini shock arrestor on the cold feed to the boiler near to where they were hearing the sounds. I also added a mini shock arrestor to the washing machine and I also replaced a stop that on cold feed to boiler with full bore lever but two weeks later they have said they have heard the noise often.

On this visit, I checked the water pressure and it is quite high, over 4 bar and this was at 3pm and so will most likely be higher at night.

They have now said the noise if from the upstairs bathroom and they think it is from the pipework to the basin which is on flexi tap connectors and the pipework goes into a void in copper and does not appear to be clipped.
I want reassurance on what to do next time. I'm thinking to quote to put a reducing valve after mains stop tap and hard pipe the basin taps instead of flexi connections and get shock arrestors on the supply to the basin taps. They had said the noise goes when opening the basin taps but they were not sure which, hot or cold..

I also had a sort to install 2 litre potable expansion vessel but not sure this will be needed and want to keep cost down, considering I failed to fix the first time round..
There is also a basic inline scale reducer 22mm after stop tap that may need replacing. The mains stop is mainly opened and I adjusted it.

Any advice really appreciated,

Many thanks

 

[Chuck]

If the pipework isn't supported and clipped properly that's an issue that should be attended to and doing so may well improve or cure the hammer problem.

Shock arrestors work best if they are positioned close to the source of the shock wave, which is not necessary where the hammering is noisiest. From your description, the washing machine is the most likely trigger (they typically have cheap snap-action fill valves that create a shock when they close.)

Toilet float valves, particularly if they are low-quality or worn out can trigger hammer, particularly if the supply pressure is high.

A PRV on the supply to limit the pressure to 3 bar should help but TBH, a supply pressure is only 4 bar isn't that high so the effect may not be that dramatic.

Hammer problems need to be tackled systematically. Pay close attention to how the householder describes the noise and when and what triggers it.

 

[Illuminate]

If the pipework isn't supported and clipped properly that's an issue that should be attended to and doing so may well improve or cure the hammer problem.

Shock arrestors work best if they are positioned close to the source of the shock wave, which is not necessary where the hammering is noisiest. From your description, the washing machine is the most likely trigger (they typically have cheap snap-action fill valves that create a shock when they close.)

Toilet float valves, particularly if they are low-quality or worn out can trigger hammer, particularly if the supply pressure is high.

A PRV on the supply to limit the pressure to 3 bar should help but TBH, a supply pressure is only 4 bar isn't that high so the effect may not be that dramatic.

Hammer problems need to be tackled systematically. Pay close attention to how the householder describes the noise and when and what triggers it.

I would of clipped the pipework but it is inaccessible as goes into a void downstairs behind a kitchen worktop and up a void to the basin. I plan to put a clip up by the basin but the pipework in the void is most likely not clipped as I can move the pipework a bit.
I added a shock arrestor to the washing machine but no luck. Apparently the fill valve had been replaced recently and it is not letting by.
I was thinking that the water pressure would be quite a bit higher at night when there is less demand and thst is when they are more often hearing it about 12 and 3am.
They said they hear it from the upstairs bathroom and they said they think it is coming from the basin pipework (that is going into the void I mentioned) which would make sense. They also said that they manage to stop the noise by opening the basin taps but they could not say which one if it is one or both effected. They just open and close both simultaneously and after a bit the noise stops but sometimes starts again a few hours later. This does not happen every night and sometimes but more rarely happens in the day..