Loud hammering noise and irregular water flow from bath taps

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Avocet

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I wonder if anyone could help me with this one please? A month or so ago, I fitted a new bath and new taps. They're fed by 22mm copper pipes. I have those braided flexible hoses for the last foot of pipe run to each tap.

All seemed fine, but in this last week, there's been a loud hammering noise and water spurting out of the taps in time with the noise. If I open a tap gently and let a trickle of water out, all is fine. As I gradually open the tap further, the flow increases until suddenly, it hits a point where the hammering starts and the water comes out as an interrupted gush, several times per second, like a machine gun. The shockwave is transmitting along the pipes as it does so. If I open the tap still further, the knocking stops and the flow become steady again. The same thing will happen in reverse, as I close the tap. At one particular flow rate, all Hell breaks loose! Above and below that flow rate, all is fine.

It happens with the hot as well as the cold tap. We have a combi boiler, so both are at mains pressure. The pressure is pretty high - about 5.5 Bar at the tap (just under 6 Bar downstairs).

Prior to me doing this work, it was all fine with the old bath. All that has changed are the taps and the last foot of pipework. I'm just a bit puzzled why it didn't do it in the first week?
 
Issues can take time to develop. Firstly are the taps suitable for mains pressure? And secondly are the hoses kinked at all?
 
Avocet said:
It happens with the hot as well as the cold tap. We have a combi boiler, so both are at mains pressure. The pressure is pretty high - about 5.5 Bar at the tap (just under 6 Bar downstairs).
Click to expand...

You really want to get a Pressure Reducing Valve fitted just after the mains stop tap. Running your mains system at anything over 3bar can, over time, cause issue with seals and valves. Reducing the pressure may also correct your issues.
 
Thanks everyone. No, the taps aren't quarter turn, they're old fashioned (although they were brand new a month or so ago when I fitted them)! They were Bristan Colonial from Screwfix. Supposedly good for 10 Bar of static pressure and 7 Bar of dynamic pressure.

@Novice - good thought on the hoses being kinked, I had a look and they don't seem to be. Although there is certainly a bend in them.

@ Madrab, I'd prefer not to drop the pressure if I can help it, as the shower only just has enough flow as it is! The house is 25 years old and the previous bath taps had worked fine until I replaced the bath and fitted these ones!

I'll ltry to upload some videos.
 
Here are a couple of videos:


Sometimes, they knock very slowly


Here are the pipes under them. They're clipped to the wall with plastic clips. The closest is a foot or so to the left from the edge of the video. They're the original clips from the previous installation. My only changes have been to fit the shut-off valves, flexible hoses and new taps.

 
Avocet said:
I'd prefer not to drop the pressure if I can help it, as the shower only just has enough flow as it is
Click to expand...

Certainly see why if your shower has barley enough flow but at a mains pressure of 5 - 6bar then I would say you have a bigger issue. At that pressure, if it's sustainable (dynamic) regardless you should have a shower that blasts your skin off.

I'd be looking at your distribution pipework as you have an issue somewhere if your shower flow is barely enough.

5-6 bar going into your combi boiler sometimes isn't too clever either, depending on the make they may specify that the inlet pressure is reduced lower than that, especially on an older boiler.

That is aside the issue you're here about of course ....

The trouble you are having is the jumper in the taps (where the washers sits) is resonating at a certain pressure/flow rate as the tap opens and the jumper lifts up off the tap seat. The brass thread in the tap body has enough play in it allowing the pressure to move the washer up and down. It may need different taps TBH. It will probably be the high mains pressure that is causing it. The flexi's won't be helping either given the play/expansion they have and @ 6 bar they won't be very happy, I'd run that in copper or at the very least plastic. Don't let that go on too long either as the flexi's won't like it.
 
Thanks Rob, that all makes perfect sense. It feels exactly as you describe when I turn the taps, as if there's some sort of "lag" between me taking the pressure off the washer and then all of a sudden it jumps off its seat, sending a bug gush of water out, but then the pressure behind it drops just enough to let the washer sit back down, whereupon, it builds up again, and lists the washer (and so on).

The boiler is a Worcester Heatslave, oil fired and the same age as the house. I don't know whether it has any pressure-reducing measures applied. However, although it wasn't a hot tap that I measured the pressure at, the flow rate from the hot tap looks similar to the cold one, so I'm guessing there isn't? It's been OK this last 25 years though.

The shower...well... er... that was probably me as well! This whole bathroom refurbishment project started with a leak from the original tiled shower, so I got one of the fibreglass "pod" jobbies. The old shower was fed from a 15mm cold pipe with a gentle right-angle bend in it to come into the back of the shower unit. I fitted a ball valve in the 15mm pipe so I could isolate it in the future. That was probably my first mistake! The hole in the ball is nothing like the bore of the 15mm pipe, so I guess there will be a restriction in there. I've then got two 90 degree compression elbows to turn the direction of the pipe so that it faces downwards coming out of the wall, then a length of 15mm braided flexible hose going in a gentle U to take up any movement of the shower cabinet relative to the wall, then a couple more 90 degree elbows to get it on to the inlet for the shower unit. I reckon, I've probably built a fair bit of restriction into the system that wasn't there beforehand! It's a Triton thermostatic shower and I bought it because it claimed 8 litres per minute and most of the others in that price range were 3-5. I haven't tried running it into a bucket, but it doesn't feel anything LIKE 8 litres a minute!
 
Yup, that'll be why there is a pulse at a certain point when the tap opens. It'll be at a certain sweet spot where the pressure is overcoming the downwards force of the headgear

The max pressure allowed on your boiler is 2.5bar but that'll probably be a water supplier requirement rather than the boiler itself. Especially if the boiler hasn't had any issues up till now.

When you measure the water pressure, ideally you want to test it static (nothing running) and dynamically (with more than one outlet open at the same time), you can also measure that into a bucket over a min and that will give you a dynamic flow reading. Yep, there's obviously something in your shower and/or the pipework to it that is restricting the flow as @ 5-6bar you should have a kick ass shower, even with normal ISO valves.

What shower is it, as @ 8L/Min isn't very clever given your mains, it isn't an electric shower is it?
 
Yes, I've been disappointed. I'd rather hoped I'd barely be able to stand up under that shower! It's a Triton T80 Easifit Plus, which replaced a Redring Expressions 500S. I had hoped it would be better than the Redring, but is actually slightly worse. It's not "awful", but just a bit disappointing. The Redring was plumbed in to the previous pipework though, which was much less restrictive.

Haven't done anything with the bath taps yet. Concentrating on the outside of the house while the weather's good.
 
Unfortunately not, there is no electric shower that I know of, even @ 10.8kw, that you classify as skin tingling. The Mira airboost showers are probably the best 'feeling' showers I have installed but even then the flow isn't very good. That's in the summer too when the incoming water is significantly warmer in comparison to winter. In the winter an electric shower's output will drop as it has colder incoming water to heat up so slow the flow to allow it to obtain the requested temperature.
 
Yes, and of course, this is only 8.5kW and I can't really justify running a heavier wire from the consumer unit, which is about as far over the other side of the house as it is possible to get! I'd certainly noticed the difference between Summer and Winter with the previous shower and it certainly seems to be the case with this one too. However, I tried putting the shower head from the Redring one on to this one and the flow rate is definitely less. It was more of a "dribble" than a "spray"!
 
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