Funny Noises

[Quillan]

This has me stumped and I am desperate for some ideas.

Our (Electric) hot water tank is starting to make a noise. Sometimes it two quick knocks like "knock knock" other times it can be "knock............... followed by < wait 4 second> a .................knock". It rather sounds like somebody is in the tank, under water, tapping with a hammer. It sounds like it echos along the pipes throughout the house and whilst its not loud enough to wake you immediately it is enough to wake you gently and not let you get back to sleep because it becomes annoying. I don't know if it's that we don't notice it during the day what with other 'household' noises but it appears to be mainly at night. Oh yes the tanks (we have 4) are on 24/7. If you put your hand on the side you can actually feel the knocking.

It's a bit difficult to find what it is. I thought it might be the heater so I turned it off and 'drew' about 20L from the tank to allow cold water in to cool it down. It did stop after about 30 minutes. Then it started during the night and by the time I got dressed and went down to the basement it had stopped and that was with the power on. My wife seems to think that it may be the dishwasher filling (even though it is cold fill) as it has happened when in use. I didn't work that one before so the last time I noted that the dishwasher was on but then why does it not do it with the washing machine on and why would the cold water side have an effect in the hot water tank? I have tried 'venting' it from the bottom with no success.

I guess the problem is that it appears to start and stop when it likes or could it be that I have done something to stop it (like turn it off and drain water) and it takes some time to take effect?

I thought I would isolate it but unfortunately the big stopcock, which is part of the vent unit, appears stuck and I can't turn it and there appears to be no other stop cock although the next time it starts I might turn off the house stopcock and turn on a hot water tap until the pressure in the pipes gets to zero.

The tank, I believe, is of the construction where the heater is in direct contact with the water. I say this because the connection and, what appears to be, the thermostat is in the centre of a plate about 10" in diameter with a load of bolts round the edge inserted in to the bottom of the tank.

Short of replacing the tank, which I am reluctant to do until I can prove it is faulty, I just don't have a clue. I have this suspicious feeling that this in one of those things that people either will say they have never heard of it before or it is so common that I get 20 replies all saying the same thing. Whatever the answer it is driving us potty and we need to get it sorted before we go mad.

[Gluestick]

Logically, Quillan it's either water hammer, being caused by a faulty pressure relief valve in the ballon or something else, such as the dishwasher if it's also on at the same time (the solenoid valves in diushwasher and washing machines do turn on and off pretty dramatically unlike a normal water tap!), or the element is furring and the knock is an uneven expansion of the element and calcite, which is then magnified through the stored water. A bit like an old boiler "Kettling".

(n.b. For those PC folks in our midst, I hasten to say that by this I do not mean one's female spouse hastening to make a cup of char - it is Friday! [:D] -  but the noise from a boiler when it's old and coated with sludge and calcite etc!).

One possible solution is to fit an " Anti Billy Goat" (honest translation!) valve in the feed to the ballon. This smooths out the water hammer surges.Your shut off valve (or stop-"Opposite to a female chicken"!) part of the system needs urgent attention: probably best to change the whole group de sécurité  as this is important if you need to drain down the system.

 

[Gyn_Paul]

You don't say if you live in a hard or soft water area. If the former, then my money's on what Gluestick calls 'kettling' I'm not sure what goes on at the micro level, but it cerftainly happens with kettles with exposed elements when they get furred up. The sound is quite a dramatic thumping. I can imagine on the long expanse of a chauffeau element it would reverberate. The key is if you disconnect the electricity from this chauffeau overnight, does the noise go away?

I really don't think venting will have any effect, as the volume of air trapped in the top of the chauffeau is fixed in that excess air will flow out of the hot pipe the next time you turn the tap on because the hot pipe terminates a couple of inches from the top.

Oh, and apparently you can beat the auto censor if you make 'stopcock' all one word!

p

[AnOther]

Are you sure it's not just temperature expansion..

My own heating system, which is partly steel pipe and partly copper, usually makes one or two quite loud "bangs" shortly after coming on in the morning and it's so transitory that it's impossible to track down precisely. Even if I could the pipe I know it's coming from is in a concrete floor so not sure what I would do about it anyway, breaking the steel run with a piece of copper might do it  [:(]

[Quillan]

Thanks for the ideas.

I rather like the sound of Gluestick's re the dishwasher but combined with the other two so this is what I think I will do.

I am going to turn the heating off on the tank (trip the main breaker for the tank) and although its a waste I'm going to run the hot water till it comes out cold. This should deal with any possible expansion problems I think and just to make sur wait about 30 mins. I am then going to run the dishwasher and see if I get the noise. If I do then would I be right in assuming its the dishwasher and this business with the solenoids turning the water on and off too quickly and that there is perhaps some sort of fault that's making it activate the solenoid as it washes? If I don't get the noise then perhaps I need to look at the tank. Can you replace the balloon or would it be better just to change out the whole tank (and fit a new security thing with a tap that works)?

[Dave&Olive]

hi ok

         it`s called the" Red Dwarf syndrome" you have been watching too many repeat episodes

 Dave

[Gluestick]

When dishwashers or washing machines are in their cycles, Quillan, they use various methods to measure the amount of water taken in: one is a simple tube with air at the top. As the machine fills the increasing air pressure trips a pressure-sensitive switch: which in turn enables or dis-enables the solenoid valve.

This can happen three or four times until the machine ajudges it has sufficient water.

Also with Cold Fill devices (most are these days), as the water heats up, the machine tends to keep adding to the water fill to adjust the temperature.

Thus cycling of filling water is quite normal.

Unlike a normal tap (even the ceramic disk types), which opens and closes less dramatically, the solenoid valves bang open and shut almost instantaneously.

You can in fact watch the flexible water feed pipes jerk violently.

The problem with water is it follows the first Law of Hydraulics: viz, fluids are basically uncompressable. There is no "Cushion" in fluid systems, thus the shock wave of water flow being suddenly stopped creates a wave of energy right back through the pipework.

Water Hammer (pipes knocking loudly) is normally created by lose pipes "Banging" against their retaining clips or adjacent joists, floorboards etc.

You can only really get to the root of this problem by deduction and focusing on causal equipment: stand by the offending ballon and task someone else to turn on the dishwasher (e.g.): see if the appliance filling and then stopping: and then starting to fill again is directly connected with the knocking noise. Same with the washing machine.

Some toilet cisterns can also cause this effect, as the float valve or other can be affected by small "waves" on the surface water as the cistern fills and causes the valve to cut in and cut out slightly; which can be enough to cause water hammer. (This effect is more usually experienced with the tank of gravity fed hot water systems where the loft storage tank has significant surface area and is thus more likely to set up surface waves in the tank).

If you do conclude the problem is being caused by the dishwasher (e.g.) then probably the best solution is to install an anti-bélier in the feed to the dishwasher.

Brico Depot stock these and they are circa € 15 and simple to install in the water feed pipe.

This is a simple expansion chamber which cushions the dynamic shock and should cure the problem.

Since French cold water systems operate at far higher pressure than the UK, for example, this is bound to exacerbate any water hammer problem.

 

 

[Quillan]

Well we have done some experimenting and it appears to be the dishwasher which in turn appears to have a fault. We can hear the water going on and off, very quickly and 'hard' just like you said and the noise happens at the same time. We also noticed that all the lights on the front of the dishwasher flicker at the same time. It does not just do this occasionnally it can do it for a minute or two, then pause and do it again. Before I rush out and buy a new dishwasher (our has been repaired once with a new pump) any ideas, could it be the logic board or something more simple?

Have to say glad I asked about all this and thanks for the help otherwise I would have changed the tank, with all the hard work and re-plumbing involved, only to be tearing my hair out because I would have probably had the same problem. So once again thanks for the help guys. 

[Gyn_Paul]

Well done Gluestick: great remote diagnosis!

Quillan, how do you feel about taking the back and sides off the dishwasher? Practically without the serviceman's diagnostic manual there's not much you can do other than check out the water level sensor. I discovered to my cost that these can be buggared by transporting a dishwasher (or in my case a washing machine) on its side thus allowing the water sitting in the sump to run up the air tube into the sensor.

In your case, if it's not a logic board problem, then the only electro-mechanical thing it might be is a blockage in that rubber tube going to the sensor, restricting the water level rising in it, thus making the sensor (which is a microswitch on the back of an aluminium bellows, flexed by changing air pressure delivered by the rubber tube) deliver intermittent signals.

Good luck... rummaging around in the mucky innards of a DW is one of my least favourite jobs!

p

[Gluestick]

Glad to be able to help! [:)]

Dishwashers are in fact quite simple bits of kit.

They are based simple micro-controllers or microprocessors, which have been programmed to create the desired dishwasher programme.

Whilst it is possible that the main logic board has developed internal faults (which are normally ancillary components like switching transistors or diodes going down), it could well be the device which measures the water level, since it is this which switches the infill solenoid on and off at the beginning of a programme sequence: it might also be the thermostat which regulates the water temp.

It's quite simple to test the water level switch: just put a meter across the terminals (disconnected of course) and blow up the tube!

The big problem is sourcing device schematics and circuit data. Some is available online. I recently purchased a motor relay for our fridge-freezer in France which died whilst we were back in England! The smell was quite interesting after a few weeks had gone by................

Cost circa £15 including postage.

Depending on make, a number of web sellers do supply spare parts quite reasonably.

If there are serious problems with the logic board this can be tricky to service, without the correct analysis tools; (A laptop and dedicated software normally).

There are a number of websites offering service info: some reasonable some not so good. With patience it is possible to find lots of data on the web even full circuit diagrams and some service info.

Eureka!

For parts, these people can be quite useful:  Eureka2!

 

[Quillan]

Well I might be getting somewhere. The bit that got me thinking was the fact all the lights on the front flickered as the solenoid open and closed. I rather thought that if there a serious problem then perhaps the breaker would trip out which it hasn't. I decided to get brave and took the front apart because that's where all the buttons are so it has to be dry and therefore the logical place in my mind to put the processor board, and I was right. Went back to basics and took all the connectors off that I could find and gave them a little squirt of WD40 and replaced them. There was an 'edge connector' so  gave this a light rubbing over with a 'glass stick' to clean it up. Reassembled and tested, the lights don't flicker and the banging noise has stopped for the moment so we will see how things go. Unfortunately with our line of work a dishwasher is a very important bit of kit to go wrong. I don't want to brag by the way but there were no screws left over when I put it back together [I] . I have taken note of the other stuff you have all mentioned just in case the problem is not fixed and comes back. Once again thanks for the help.

PS. Any idea what the life expectancy of these things are? We use ours once a day during the winter but as much as three times a day between April and September and its coming up for 7 years old.. We had thought of getting a professional one but you are talking about a couple of grand and we didn't think it was justified.

[Gluestick]

Glad that seems sorted.

Using appliances every day will normally make them last longer, since pumps stay free.

Unless you need the capacity commercial dishwashers won't necessarily last any longer.

In the UK we are still using a washing machine that's now 25 years old. Main reason, mechanical programmer no clever electronics, no little umbrellas.

It's now had three programmers, two emptying pumps and one drive belt. When it goes soon it, will be replaced by an AEG machine, as these are now the only one made in Germany: even Bosch are now made in Turkey!

My philsophy with all this is if it aint broke...................................