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Yeah agreed - seen your other posts on arrestors. It depends on the time of day. Sometimes it's just one click on tap closing. Other times it's with open and closing. The lever taps in the house seem to produce the worst sounds. But then it doesn't explain why this doesn't happen when hot is...

Ok so one question, if it is a pressure spike causing the hammer you're saying it should go through the NRV and the EV takes up the shock. But what if the HW connection after the NRV is also pressurised - isn't that why we have EVs? Just trying to understand this part. There's no tundish...

Video. Opened the old tap 3 times. Then switched to hot for a brief moment. Then cold again 3 times. Notice how the hammer pattern changes

There is a blending valve. Never need 100% sure what this does. Yes hard piped.

Yeap back again this morning. But it was after I opened the hot tap the cold started doing it again

Could pipe routing have an effect on this? I only ask because with it being a new build there's other houses but the plumber has done slightly different routes to to get to ICG. Mine has a lot of sharp 90 deg bends in it. Yeah before that I'm tempted just to fit an arrestor to the balanced...

Yeap got all that. I can't see a problem either. What are the chances of two ICGs being faulty and behaving the same way? Hmmmm. Well I de-pressurised the system about 1.5 hours ago, used every tap in the house, toilets, HW heating on, even running the washing machine. No noise yet. I want to...

I waited for reheat that time. I just did the same test now without waiting for heat just to see if that makes any difference. Did the same thing. It stops hammering for a bit. Something then happens over time which makes it all come back. It seems from de-pressurising it does something that...

So it doesn't really make a difference then if a hammer arrestor is before or after the ICG...

Yeah I'll remove it at some point. I just had a theory at the time it was going from 4.5 to 3 in the ICG that it was too much hence the hammer. I waited till it reheated, Thats why the cylinder inlet was warm and the pipe leading up to the EV. Yet it didn't hammer when running a cold - no noise...

So everything is yellow is contained under the kitchen cupboard. Probably no more than 1m long. Everything in green is in the cylinder cupboard. The pipe leading to the cylinder from the kitchen is probably a good 10m long as it weaves between joists above the ceiling and up about 4-5m from...

I set it so it doesn’t spike above 3.0 bar when the kitchen tap (which comes off the mains) is closed. Dynamic pressure reads around 2.2 Bar Either way it didn’t make a difference to the noise on the ICG.

I know which taps are causing it. The problem is it only happens ever after hot water has been drawn and then if you use any cold water it clunks. If I've drained the system then repressurised or leave it overnight to settle - it's quiet - unless that's because the pressure built up in the HW...

One other thing I really don't get - last night I drained the entire system and opened the taps. Refilled it all. If you use the cold tap it didn't do the hammering. As soon as you switch to hot you hear the classic clunk noise once and then if you switch back to cold it hammers continuously...

It was spiking to 7-8 bar when the kitchen tap or dishwasher valve closed. When flowing it was reading about 4-5 bar. The ICG was seeing the full force of this.

No they tend to close slowly as the float rises up. If the taps are closed really really slowly you can avoid the hammer but it’s just not practical

Thanks that diagram really helps! I'm wondering if it's the balanced cold causing the problem then. I'm going to fit a T here and see if I can take some pressure readings.

Sure can - which bit do you want to see?

Wait isn’t the NRV between the balanced cold and the UVC EV/cylinder feed? It’s what stops hot water going back into the balanced cold?

Yeap