Bosch dishwasher series 4 knocking noises when water stops filling.

GillyLucy

We recently had a new Bosch series 4 dishwasher installed to replace a 15 year old Lamona machine.

From day 1 there has been a knocking noise when the water cuts off - sometimes the sound is minimal & other times can be heard above the TV in the next room.

Contacted Bosch who send an engineer who tested the machine and has reported : 

'On test through two test cycles filling from heat exchanger and inlet valve no unusual noises observed

Customer made fully aware that no fault has been found with appliance but the position of the isolation tap would benefit from being adjusted as this appliance is fitted with an aqua stop safety device '


Typically there were no  really  loud knocks when he tested but the normal cycle is well over 2 hours so not a real world cycle as such.

Before I contact a plumber to move the position of the isolation valve (not really sure what this will
achieve anyway)  has anyone else had this issue & if so how did they resolve?
Many thanks.

ThisIsWeird

Can you replicate this knock every time, reliably? If so, try it with a cold tap partially running - say a quarter on - in another area - a bathroom or similar.

Does it still knock?

Trying to see if it's a 'fault' in your plumbing and not the machine - ie a pipe that 'hammers' when the water is turned off quickly. The valves on WMs do shut off pretty much instantaneously, so a slightly loose pipe can 'shudder' with the change in pressure.

Can you tell where the sound is coming from?

And could you post photos of the current isolating valve, so we can suss what the guy was talking about there?

GillyLucy

The thing is we never had this with the old dishwasher , it has only started to knock with the new one.
I will try the cold tap running when back at home .
It is an integrated machine so reluctant to take out again!!

Keep_pedalling

GillyLucy said:

The thing is we never had this with the old dishwasher , it has only started to knock with the new one.
I will try the cold tap running when back at home .
It is an integrated machine so reluctant to take out again!!

You previous DW probably did not have a valve that shuts of the water flow instantly. This could simply be poorly secured pipework reacting to the shock wave caused by the rapid stop in flow created by the new DW.

GillyLucy

Keep_pedalling said:

GillyLucy said:

The thing is we never had this with the old dishwasher , it has only started to knock with the new one.
I will try the cold tap running when back at home .
It is an integrated machine so reluctant to take out again!!

You previous DW probably did not have a valve that shuts of the water flow instantly. This could simply be poorly secured pipework reacting to the shock wave caused by the rapid stop in flow created by the new DW.

That could be the case , the old one was very basic (even so - it lasted 15 years!) . It may be the Aquastop is not working well with the old pipework.

Keep_pedalling

GillyLucy said:

Keep_pedalling said:

GillyLucy said:

The thing is we never had this with the old dishwasher , it has only started to knock with the new one.
I will try the cold tap running when back at home .
It is an integrated machine so reluctant to take out again!!

You previous DW probably did not have a valve that shuts of the water flow instantly. This could simply be poorly secured pipework reacting to the shock wave caused by the rapid stop in flow created by the new DW.

That could be the case , the old one was very basic (even so - it lasted 15 years!) . It may be the Aquastop is not working well with the old pipework.

More like the other way round 😄 Try reducing the flow by moving the isolation valve to half way open. 

Lorian

My Bosch dishwasher has a very aggressive aquastop valve and caused water hammer. I fitted a Sioux chief water hammer arrestor and that sorted it  you can get them at DIY/Screwfix/amazon.

GillyLucy

Lorian said:

My Bosch dishwasher has a very aggressive aquastop valve and caused water hammer. I fitted a Sioux chief water hammer arrestor and that sorted it  you can get them at DIY/Screwfix/amazon.

Have now looked at these & sounds like low cost fix , so thank you,  will source and find someone to install .