intermittent plumbing knocking.

[jockskinner]

Hi Folks,
I am struggling to track down a knocking which appears to be coming from my kitchen plumbing. It is intermittent so it is difficult to track down because sometime I get a thump every hour or so , or sometimes through the night. the loud thumps are always in ones and appear to come from one end of my kitchen My mains supply enters under my double sink and travels to a washing machine next to the sink, then a dishwasher next to the washing machine and up to a combi boiler on the wall. The hot and cold then goes to a shower room in the next room and upstairs to my bathroom. I have had this problem for about a couple of years as I thought the sound was coming from my nextdoor neighbour banging a cupboard door.

 

[gigz]

Does it happen with all appliances off or is any of them on ?

 

[jockskinner]

Hi Folks,
My wife says it sometimes happens when the dishwater is on, I have heard it after someone has flushed the downstair toilet. I have heard it after I have washed something in the sink .....other times it does it for no reason, nothing on and no water turned on.....spooky.

 

[jockskinner]

Sorry, I forgot to mention that when I had my boiler serviced a couple of months ago I mentioned the bangs to the engineer and he said it was something to do with pressure valves or pressure equalising???

 

[gigz]

Do you have any quarter turn taps ? Try turning them off quickly and see if it bangs, if it does try turning your stoptap up or down see if this helps. Sounds like water hammer. Washing machines and dishwashers stop the water quickly causing this sometimes.

 

[jockskinner]

Hi again,
Yes, both the dishwasher and the washing machine have these valves and are situated under the sink and close to the mains water input....I will go and give them a turn and see if they do as you say...Thanks.

 

[jockskinner]

Hi Gigz,

Turning the valves open and shut (1/4 turn) had no effect but I have noticed that there appears to be some kind of trap fitted to one of the appliances between the valve and the appliance.

 

[gigz]

No i didn't mean turn the valves, i meant internally the WM/dishwasher have fast close valves. Have you got taps that are quick closing (quarter turn) or are they the type that you close down slowly ?

 

[jockskinner]

HI gigz,

I am not quite sure what you mean by taps? Both the washing machine and the dishwasher are integrated and would be difficult for me to get a look inside. Is there a simpler way to check this by say...Turning the supply valve off for the dishwasher for a day and the next day repeat the same procedure with the washing machine. I have no idea how the kitchen fitters installed these machines.

 

[gigz]

I mean, some taps (sink,bath,basin) can be closed quickly (quarter turn) whilst others close slowly (traditional). A lot of water hammer problems (banging pipes) are caused by the water stopping suddenly, adjusting the stop tap can (sometimes) fix this.

 

[jockskinner]

Hi gigz,
I understand what you mean now about taps, I thought you were still talking about the washing machine and the dishwasher. The hammer sound appear to come from under the sink and the sink taps are quarter turn. I will try this tomorrow morning. All the taps in the house are quarter turn and the problem appears to be related to the cold water supply.
Good night.
Jock.

 

[jockskinner]

Hi Folks,

Unfortunately turning taps on and off has had no effect. I did this last night and there was no hammer noise at the time,(11.00 pm) but there was a noise about 2.00am and again about 5 ish am. Nothing was switched on and no taps or cisterns were used.. My wife said that she heard it about 7.00 am after she flushed the downstairs toilet and I have just heard it about an hour ago whilst reading my paper.

 

[jockskinner]

Hi Jeff,

Good of you to jump in to help a disabled pensioner, every little helps. I haven't heard from gigz since Friday night when I had to go to bed due to my angina problems.
I am thinking that I may try a water hammer arrester firstly on the washing machine input hose, (its on every day) and if no change, swap it to the dishwasher hose (which is on every other day).
Whad ya think, gasman?
best regards,
Jock.

 

[jockskinner]

So Folks,

Is there no answer to the knocking problem and would one of these arrester things help ?

Jock.