Hello,

It seems other people have had this problem, and I've been through here and tried all the remedies I have found over the last few months, however, the foghorn sound is still an affliction in our house. It started in the upstairs toilet, and now sometimes will happen in our second toilet downstairs. Not every flush either, just randomly happening at all times of the day and night.

What I've tried so far


Added dishwashing liquid in the cisterns (this worked for a time, so thought it was an old washer).
So, replaced the outlet valve washers and the wedge washers, cleaned out the cisterns of dirt as well (again, this seemed to work for a few days but it returned).
Flushed out the system by turning all taps on and flushing all the toilets in turn.
Then replaced the fill valves (fluidmaster 400UK replaced by new units of the same). Still, no improvement.
Had a plumber out, but couldn't reproduce the sound. He guessed water hammer and there was nothing anybody could do about it!


Things I have noticed


Turning on the closest tap will stop the sound, and having the tap running first when flushing will cause it not to happen at all (this has become our workaround at the moment, but is annoying).
When replacing the fill valves, I noticed that there was a small white rubber cone inside the shank. I had to remove this to fit to the toilets as the pipes leading up to it would not fit otherwise (slightly too long). The old fill valves I replaced had the cone removed, so I didn't see this as a problem when I did it -- but now am thinking it might pay to get a shorter pipe and another set of fluidmasters keeping the cone intact. As far as I can tell the cone reduces the flow of water...


Any suggestions very welcome! I think the next step will be to look at the taps on the wall leading to the toilets — perhaps looking at replacing these?

Before we get into the fix I would really benefit in knowing exactly what your water pressure it in the home. If you don't know it you can attach a pressure gauge to you garden spigot, should be in the ball park of 40 psi. Most foghorn sounds from a toilet are the diaphram in the fill valve vibrating. Could be a bad diaphram or way too much water pressure

Okay I don't have a gauge but will aim to get one in the next few days. Would it be better to measure it from the tap leading to the toilet, or is the pressure the same from all outlets?

Just supplying an update -- I had heaps of trouble finding a water pressure gauge. Finally found one but it not the right fitting end (far too small).

But... I noticed that both our outdoor taps have pressure reducing attachments on them. I'm assuming they're been on there a long time (place is 15 years old) as they are impossible to remove.

Might this be a sign of a high pressure? If so -- what would be the next step to look for a solution?

Dirt, the pressure gauge should be available at any big box or hardware store and connect to the hose bib just like a water hose would.

Are you saying that you have two pressure reducing valves? PRV's are adjustable, after you install the pressure gauge you could try to adust there. Good luck

I assume you are located in the UK. Therefore certain translations of what the normal plumbing practices are has to be done.

The fog horn sound is caused by something vibrating as the water flows, usually a loose washer in a valve. Its occurrence can vary as the flow and pressure varies.

What we call water hammer in US occurs when a fast acting valve, such as a toilet or a single leaver faucet closes quickly. The sudden stoppage of water causes the pipe to move, banging against a structural member. This creates one loud sound like a hammer blow. It is usually a single bang or sometimes two.

Yes, the static water pressure will be the same at all faucets or taps. Here we would not have a pressure reducing valve on an exterior faucet. Since these are used primarily with garden hoses, we would want all the pressure we could get. We do however use anti-siphon valves. These are to prevent contaminated water from being siphoned back up into the water system from the garden hose. Something that can only occur in extremely rare conditions. A combination of conditions so rare they only occur theoretically, but it made somebody rich.

Here, pressure gauges are readily available that fit onto the exterior faucet or tap. These gauges also fit the end of the hose.

As stated earlier, the fog horn sound is caused by vibration. If it occurs at one toilet one would suspect a vibrating washer in either the toilet fill valve or the stop valve on the supply line to the toilet. If it occurs at more than one toilet one would suspect either the fill valve, the stop valve, a valve further up the line such as the main shut off valve to the house. Do you have a pressure regulating valve where the water line comes into the house? These can also create the vibration.

Sounds can be difficult to locate. Putting your hand on the pipes when the sound occurs can help to locate the source. The closer you are, the greater the vibration.

Turning on an additional tap changes the dynamic pressure and the water flow thus creating a different frequency of vibration which you might not hear or might not cause the loose washer to vibrate.

Next time the sound occurs start feeling the pipes to locate the source. Since you have changed out the fill valves, I think you have eliminated those as a possibility. That leaves the stop valves and the main shut off valve and possibility a pressure reducing valve.

The cone shaped rubber device in a FluidMaster kit is not a pressure or volume reducing device. It is seal for a certain type of connection.