Expert: Dana Bostick - 6/10/2009

Question
QUESTION: After a shower upstairs in 1 bathroom but not the other -when I turm the kitchen sink or bathroom sink on(not off) downstairs the pipes make a bang/rattle sound-seems to come from around the hot water tank-after a 2-3 seconds it is fine and will not do it again-will go 2,3,4, days before it happens again,had son help and it seemed,after he turned off the water, that it kept running for @ 30 seconds - this just started last week - water tank is 5 1/2 yrs old - pressure regulator was replaced in Oct 2008
Any ideas? One other thing - seemed like air came though the faucet one time -like I was bleeding the system.

ANSWER: Hello Mike,
This sounds like the water heater is making noise.  When you draw off hot water, cold water replaces it and needs to be heated again. If the water heater has a lot of mineral build up in the bottom it will bang and clunk.  This sound gets transmitted though the pipes.

If you read the installation manual for the heater, you will find that the unit needs yearly service which consists of "flushing" about 1/3 of the water out of the bottom of the tank via the drain valve at the bottom.  This valve is sometimes called a "boiler cock".  If this is not done regularly, a build up of minerals forms into a cake and this causes the water at the bottom, under the cake to boil since it is sort of trapped.  The cake rumbles and bangs around inside the metal tank, making noise.

At this point, you might be able to still flush it out but maybe not.

Good Luck,
Dana

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QUESTION: About twice a year I draw off about 5-6 gallons of water and it is crystal clear - so I stop at 5-6 gallons.
If I take a shower in bathroom 1 - there is no problem or if the dishwasher is on - the problem only occurs when a shower is taken in bathroom 2. Why would it be so intermitent, plus it only clunks when I turn on the downstairs faucet (hot or cold) - which could be 10-15 minutes later and then the noise is gone.

ANSWER: Hi Mike,
First, well done for actually doing what most do not do and servicing the heater.

If it is not the water heater then there are loose or rubbing pipes somewhere. Possibly some strapping came loose. Water moving inside pipes has a lot of kinetic energy. Starting or stopping the water flow can transfer this energy to the piping system causing it to move. This mostly occurs on a quick shut down like a solenoid of a dish washer, clothes washer or the fill valve on a toilet when it shuts off. It can occur on start up as well.

Another possibility is expansion of the actual piping as it is heated or contraction as it cools. The pipe physically "grows" in length a bit as it heats and this can cause it to rub on the structure, creating noise.

These conditions can be hard and time consuming to pin down and fix. Try to duplicate the condition and have someone else stationed in different spots to try to isolate the noise.

Water is a great conductor of sound.  It moves 7 times faster in water versus air. This can mask the actual source, making it hard to find.

It seems that your problem is isolated to the one shower and that will reduce the area to "sleuth out".

If the problem is water hammer rather than thermal creep, you can install water hammer arrestors on the piping to reduce or eliminate it.

Hope this helps.
Dana

---------- FOLLOW-UP ----------

QUESTION: Just ran shower and looked for problem.  Seems to be tank.  Hooked hose up to tank drain and opened up - banging and popping - water spurted out and then the banging stopped and water was an even flow -- opened up anthoer turn --same thing bang/pop - water spits out then all calms down another turn same thing all noise comes from bottom of tank near drain-- however water is clear the whole time - pipes do not seem to bang or move - is it tank or presure or the new regulator or air (need expansion tank)- this is a 5-6 yr old AO Smith gas heater

Answer
Hi Mike,

A couple of things could be happening.
1. The sediment build up is one big chunk now so it won't flush out.
2. When you draw off water, new water enters the heater via the dip tube which injects the water towards the bottom of the tank. This cools the water in the bottom enough so that it stops "boiling" and the banging stops.

Try this; Turn off the burner. (turn it down to "vacation") so it does not come on when hot water is drawn out. The banging should not occur anymore. If so, the deposits have hardened into one chunk.

You might be able to get it out by draining the tank completely, removing the drain cock and inserting a long screwdriver in the tank and breaking it up. Keep flushing and crunching till you are pretty sure you got all or most of it.  BTW, the drain cock is 3/4 inch pipe threads so a nipple can be use in its place for draining. A nipple has a bigger opening as well and will allow more junk to drain out.

I know it's a PITA to do this but it's about the only way I know of other than replacing the heater. For this to have happened in a short even with you servicing it, your water must be wicked hard. Maybe a water softener is in order.

Good Luck,
Dana