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Question DetailsAsked on 11/27/2015

whenever the water is turned on there is a fog horn sound

What would mage a fog horn sound when any toilet is flushed or washing machine is filling with water?

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1 Answer


You notice this is happening when there is only high water demand (washer and toilet - I would bet tub at full flow will do it too. Generally caused by either a lot of air in the pipes, rarely by rapidly chattering unrestrained pipes, or a flow constriction that is causing cavitation (vortices and air bubbling) in the pipe.

Can be tough to track down alone, usually quite easy with two people - one running the water (flushing toilet in your case), the other listening for where it is coming from. Cheaper to locate cause yourself first than paying a plumber an additional half to full hour to do it. Common locations - and you can determine which are likely based on whether only happening when one flow source is used, or in your case several -

1) high flow through chattering or restricted appliance flow valve - dishwasher, washing machine, toilet, or kitchen spray nozzle inlet valves; and toilet tempering valve are very common sources.

2) flow restriction in pipe due to mineral buildup (so usually progresses with time) - can be anywhere in piping, more commonly in hot than cold, but not real commonly the cause except in quite old (40+ year old) pipes.

3) flow restriction in water heater (would occcur only when drawing quantities of hot water)

4) flow restriction in backflow preventer, pressure regulator, or inlet valve - usually at or very near where water line comes into the house, and would happen equally with hot or cold usage

5) flow restriction or blockage/breakage in circulating pump on constant hot water circulating system, heat-pump water heater, hydronic heating system - but would occur as long as system is heating/running, not just when toilet or washine machine is filling

In your case, since two sources, sounds like #1 likely out (unlikely 2 sources would start doing it at same time) - see if happens when running washing machine on cold/cold setting, as that would eliminate hot water heater if that stops it from happening. Flushing toilet tells nothing in most cases, because most have a tempering valve that mixes hot and cold water to reduce condensation on the tank, so drawing from both.

Then see if dishwasher, kitchen faucet or bathroom faucets on full flow (both temps) does it - might narrow it down to a particular part of the piping system, or might not. If they do, then try only hot or cold to try to isolate it to only hot, or when both are used. Also - try running hose bibs (hose faucets) full flow to see if that does it - might tie it down to particular segment of piping. If you have a low point drain hose bib just after the incoming falve/pressure regulator/backflow preventer, put a hose on that to drain safely and try that - if does it, would pretty much limit it to one of those devices.

One very tough one to tie doen can be a backflow preventer valve in the toilet tempering valve (also called toilet mixing valve) chattering and not seating fully - would make noise when a toilet is filling, but could also pull water through it backwards when washer or other high demand is occurring. Looks like this typically -

and generally located in basement, crawlspace, garage, etc underneath where the bathrooms are - sometimes more than one if a bathroom is significantly isolated from the others. When toilet is filling and making the noise, hold hand o ear or use a tube or some sort to listen at it to see if it is the source - if really howling you can feel it vibrating the pipe.

One other possible source - rare to hear loud indoors, but possible, especially if meter/shutoff are indoors - is a partial blockage at the main shutoff valve at the water meter, or in the water meter - again, feeel/listen to determine if that is the source. If so, depending on who "owns" the meter, might be your responsibility or the water utility's - might be worth a call to them if coming from there.

Occasionally, you will get a lot of air into the pipes because there was a water outage, or during repairs or such they emptied a water main and it filled with air that then moved down the line when they recharged the line - solution in that case if just run water (hot and cold both) at all water demand points till the air is out - till it stops spitting, spraying, splattering, or gurgling as the water comes out.

Once you tie it down but it is not air in the pipes (which you can solve yourself), or maybe not if you can't figure out the source, Plumber would be your Search the List category for a repairman.

Answered 5 years ago by LCD

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