Weird Waste Pipe Woes

[Deejay]

Morning DF

Did you try it on a cold rinse?

I've just spotted Zeddedheds earlier post about thermal issues.

I still think he may be right. Don't forget that the water pumped out of a D/W might be at 70 degrees.

In your case it probably goes in to the stack just above the underground pipework, which will most likely be rock solid. Any expansion will have to be taken up in the PVC above. What I can't see is why changing the appliance should make a difference. The only relevant things that may have changed are the flow rate and temperature of the waste, unless by coincedence the top of the stack has got blocked, as N0legs suggests. Odd, innit?

Cheers

Dave

 

[RogerS]

Does the soil pipe have an open vent or an air admittance valve?

You beat me to it. I was going to suggest that the air-admittance valve was sticky and that the volume of water expelled from the new Bosch (if at a higher rate than the previous d/w) would create a partial vacuum in the stack - alleviated by the sticky AAV opening up and going bang.

 

[doorframe]

There's a chinese hat on the top of the vent, but that doesn't prove it's clear. As a test last night I shone a torch up at the vent when running away my bath water (I do like it very hot). Enough steam/vapour in the torchlight to suggest it's clear. The hot bath water doesn't produce the banging, and there's lots of it, so that sort of rules out expansion.

But, before bed, I turned on the d/w as usual, and backed off the isolator until it was only allowing a trickle. SWIMBO is sure the noise was less. I wouldn't know. I slept through it. I'm going to order a pressure reducer and give it a go. Hopefully that will sort it, but it doesn't explain why the noise is from the stack.

Did I mention, I hate plumbing?

At the weekend I had to replace the heat exchanger on my 2 yr old Biasi condensing boiler. The dhw pressure was creeping UP on it's own, and the relief valve was letting out. After doing that, I went to run the ch and all I got was cold rads. The diverter had decided to stick! Fortunately, a dismantle, and a general jigger about got it going again.

Now, if I could just get this d/w issue sorted!

Did I mention, I HATE PLUMBING!!!!!!!!!!!

 

[Distinterior]

I still think there is a poorly clipped Cold water pipe somewhere that is VERY close to your 4" Soil pipe and it is jumping when the D/W valve closes abruptly. I have come across this situation on a few occasions during my years of fitting kitchens & Dishwashers. The problem tends to happen far more often when the mains cold water pressure is high, as yours is.

Is the Cold/Hot pipework in the house copper or plastic?

Tim.

 

[doorframe]

It's all copper, well clipped, and doesn't touch the waste. I know because I replumbed the whole house about 9 yrs ago. But, I will access the pipework where I can and have a closer gander.

 

[Distinterior]

One thing you could try.........Disconnect the Aquastop device from the Blue valve underneath the kitchen sink.
Get a spare W/M hose and connect it onto the blue tap. Get a bucket and put the other end of the hose in the bucket and turn the blue valve on and off really quickly and see if you can reproduce the banging. Alternatively, if your kitchen tap is a 1/4 turn ceramic disc tap, try turning it on and off really quickly, it should produce the same effect as the hose- in- the -bucket trick.

Tim.

PS, Where abouts in Essex are you Doorframe? If you're local to me, i'd be happy to pop round and take a look for you....!!!!

 

[doorframe]

That's worth a try Tim. I'm in Sunny Basildon, no not exactly 'just round the corner'. Thanks for the kind offer, though.

I have tried the quick on-off on the tap, but no joy there.

We did have a duff garden tap that caused banging a few years ago (as SWIMBO reminded me). Don't know why, but a new tap sorted that. I had completely forgotten about that.

I've ordered the pressure reducer, so I can set that right down to 1 bar or even less. Fingers crossed!

 

[No skills]

Probably of no use at all, do some exterior taps have a one way valve in them? Wonder if the new washer has one as well and is causing the problem.

Sorry, random thought there.

 

[doorframe]

Well. last night I backed it off to the tiniest trickle I could, and, ......NO MORE NOISE!!

You chaps were right. Definitely hammer on the cold pipe. It must be touching the stack somewhere, as Tim says, although I've absolutely no idea where. It's also strange that it doesn't do it on the first fill up, but only during the cycle. But, who cares now. I'll fit the pressure reducer at the weekend and breathe a great big sigh of relief.

Thanks for all the help and suggestions.

 

[Schoka-Cola]

Does your soil stack vent above the eaves or does it have an air admittance valve (Durgo valve) on the end. If so it might be that.

 

[doorframe]

Thanks for your thoughts Schoka-Cola, but it's been proven (much to my surprise) that it's water hammer in the cold feed that's causing the banging. This week has been blissfully quiet.