Not sure what this noise is....

[AK87]

Its a vibration from the cold pipe to the water heater (Gledhill Economy 7 water cyclinder). You can be running the hot or cold tap when this happens.

Sounds like someone is drilling into a wall. All I can seem to find online is that its water hammer, but the only example I can find is on this clip at 20seconds http://youtu.be/7qn_5Y_xKRE?t=19s, and a comment on their said its not water hammer.

I'm confused, anyone like to help me out here?

 

[Johnmelad]

That is water hammer. Water hammer can not happen when water is flowing, but in that video something is stopping the water from flowing intermittently.

Can't help you with your problem, even being on site seeing and hearing the effect can be difficult to diagnose and can be time consuming.

 

[footprints]

Like Johnmelad says you can spend hours scratching your head even when you are on site.
I'll have one pop at it, the video looks like something in the tap is loose and viabrating like the reed in a musical instrument, in your case the first port of call would be any stopcocks on the main comeing in from the road to the appliance. Many have a "floating" washer/jumper, so it can rotate as it is scewed down on to the seating to reduce wear, changing it or fixing the loose part can often sort it even altering how much it's turned on may help.

Good luck
footprints

 

[Elkato531]

My first thought would be that the washer in ball cock feeding your cold water tank is vibrating. This can happen as the washer gets old and stiffens up. This can set up a loud drilling type noise in the rest of the pipework if it coincides with the resonant frequency. You may be able to make the noise on cue by holding the ballcock slightly open. Easy fix, just replace the washer or the whole ballcock.

 

[AK87]

My first thought would be that the washer in ball cock feeding your cold water tank is vibrating. This can happen as the washer gets old and stiffens up. This can set up a loud drilling type noise in the rest of the pipework if it coincides with the resonant frequency. You may be able to make the noise on cue by holding the ballcock slightly open. Easy fix, just replace the washer or the whole ballcock.

From what you've described it sounds like you might be right. Happened again today, seems like its loudest at the top of the cylinder so i'm assuming that the washer/ballcock that needs replacing will be in there.
Not so easy though, the cylinder is in a stupidly tight cupboard!

Will let you know how I get on

 

[Elkato531]

The ballcock will be on the tank which feeds the cylinder. If you have a combination cylinder, it will have a small cold water store on top of it. If its a normal cylinder, the cold water store will be a separate tank somewhere above, usually in the loft.