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Hi all

A few months into a new rental within a large modernish development. We are fully electric and have a Redring immersion system for all hot water. I attach a picture of the overall setup 'Setup.jpg'.
Setup.jpg (92.88KiB)Viewed 3538 times
Since moving in, we've heard an appalling foghorn noise when flushing a toilet or using taps at certain times. Here's the pattern:
  • Far more likely first thing in the morning.
  • More likely after a period of not using water for a chunk of the day.
  • If I open any cold tap at start of day, it runs cold for 10s, fully hot for 30s, noise sometimes occurs, and then slowly it abates to cold again. I have been told the hot coming through the cold tap is likely a different issue, but no-one has adequately explained why (they've just claimed it's probably a back flow through a mixer tap valve or something).
Here are two videos of the issue occurring. is a flush, is a tap. Both were taken early morning.

We've had multiple visits from engineers from a respectable and professional outfit. Two interventions have occured so far:
  • Replacement of cold water inlet valve.
  • Reduction of pressure vessel from 3 bar to 2 bar.
Both together have reduced incidence of the noise but not enough. When the noise occurs, it is still as loud as previously, though length of sound tends to vary.

Has anyone had any experience with this kind of issue before? What are the engineers missing? They've seen the flush video, but I don't feel they really grasp (1) that any water flow sets it off, and (2) that the hot water flowing through the cold tap first thing in morning seems like not a coincidence.

One other thing - see 'Return Bung.jpg' and compare it to the (further away) shot from 'Setup.jpg'. The bung (or whatever it is) looks to have 'come out' over time, with the rubber seal now proud from the tank itself. If the issue above is pressure related, could this be another symptom? Maybe not, but worth also checking with the community from a safety point of view.
Return Bung.JPG
Return Bung.JPG (213.71KiB)Viewed 3538 times
Reading around, it seems even a fault at the appliance end (could be any of them) might still cause the noise from the cupboard where the cold supply comes in. Is that right too? The sound is definitely originating from the cupboard with the cylinder and cold supply.

When I've observed and touched during a long vibrate, the pipe immediately above the tank (and connected to it at the top) as well as the one with the cold supply vibrates. I can't say for certain if it's just that pipe or I'm just feeling the vibration there but those are the only ones I've checked. Difficult to discern which is the 'source' vibration pipe.

One other thing - It does seem that opening a tap really slowly, letting water draw out, and then flushing simultaneously, stops likelihood of flush causing the noise. But with caveat that sometimes even just using taps causes the noise. Flushing (either of two toilets, one ensuite, one just off hallway) causes the worst incidences as water is pulled to refill cistern.

Appreciate any help.
Keefy wrote:
February 25th, 2021, 9:32 pm
101% of the time I've found replacing the ... e&ie=UTF-8 in the toilet cistern cures the 'foghorn' noise.
yup, going to be the fill valve diaphragm or a tap washer somewhere, simple as that.
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