Banging pipes dishwasher

[stender]

recently moved in to a new house and facing a few issues. The main one being whit our dishwasher. When ut’s On we regularly get a loud banging noise which I believe is coming from the pipes somewhere. It doesn’t happen straight away and only does it for a few seconds at a time intermittently. I’ve tried pinpointing where the sound is coming from but it usually stops by the time I get to it. It only happens with the dishwasher. We have also noticed some rusty marks on cutlery from dishwasher but I don’t know if related? It’s a integrated neff dishwasher. We have a valiant combo boiler and an immersion heater and water pump and water tank. That takes me to another thread as to why I have a combo and immersion!

 

[terryplumb]

Could be water hammer . when d/washer takes water in ,the solenoid closes instantly when no more water is needed. The sudden arrest of flowing water causes the knocking sound. You could try closing down the isolator on the dishwater water supply ,it MAY stop it. If not an arrestor /accumulator should. Do you have the same sound when washing machine is used ?

 

[stender]

Only the dishwasher. The heating makes a few noises but nothing like when the dishwasher is on. It’s not a one off bang like I would expect with a valve closing, it’s usually 2 or so bangs grouped together over a few seconds.

 

[terryplumb]

If the sound happens only when dishwasher is working ,and particularly when it STOPS taking water in ,its likely water hammer.

 

[stender]

Where does an arrest or need to be fitted? It’s integrated so would have to take it out to get to the pipes and would it be the cold supply?

 

[terryplumb]

Can you find the isolator for dishwasher ,where the flexi hose from it joins pipework ? Sometimes in cupboard next to dishwasher. If you can ,try closing it half way. See if it makes a difference ,sometimes it will ,but not always. The pipework needs checking ,for adequate support , which can also exacerbate water hammer. An arrestor would usually be fitted close to the problem. Dishwashers only take cold water in ,not hot.