Dripping sound inside my domestic hot water tank

[MarkMas]

Some of you engineering / plumbing experts must know what this is about...

From time to time over the past couple of days I have been hearing a loud rapid dripping noise inside the hot water tank on my domestic system, which is a fairly new pressurized system heated by an old oil boiler. Just now (1am), the dripping was very loud, as if water was rapidly being dropped the full height of the tank, but it has gradually stopped after about 10 minutes. Definitely does not seem to be a leak outside. Should I be worried?

 

[conaero]

I am no plumber but I do understand how the hot water tank/store works.

The tank consists on a central winding which acts as a heating element and contains the 'dirty' water that's been through the boiler and circulates your radiators. Surrounding this tank heating winding is fresh/clean water from your loft tank.

This clean water is heated via conduction by the central winding containing the heated dirty water.

Clean and dirty heated water never mix and the clean heated water comes out your hot taps.

So, back to your issue. You probably either have air that needs bleeding off of the boiler heated dirty side or whatever valve supplies the clean water to the tank is sticking.

Check the ballcock in the loft tank and there is sufficient water or bleed your boiler.

Other than that, it's a heating engineer I feel.

 

[MarkMas]

Just to complete the story, the tank is now making a quiet but fast dull dripping sound, plus an occasional plashing sound as well.

 

[conaero]

Around the tank there will be several isolator valves usually with a big red turn wheel on them. They can weep and stick/block with scale. Cycle them all and make sure they are all fully open.

If the isolator valve that supplies/isolates the fresh clean water to the tank is only partially open it will cause the dripping sound you describe.

I take it someone has recently has a bath or shower and part emptied the tank and the tank is trying to refill?

 

[allandwf]

Are you sure it's not something expanding or contracting? When does it do it, constantly or at a certain point?

 

[jasst]

Ok, as I am a qualified plumber we need to correct a few things. You say it is a pressurized system, so in that case you do not have a tank in the roof to feed the cylinder, it is fed directly from the mains. Is there a separate pressure vessel in the vicinity of the cylinder? if not then yours possibly has an internal diaphragm to take up the expansion of the water. There should be a safety valve coming out of the side of the cylinder, near the top, connected to this should be a device called a tundish https://www.google.co.uk/search?q=t...h=641#imgrc=iVRkvdZyaSNTuM:&spf=1499679213870 this is designed so that you can see if the safety valve is letting by, ther should be NO water dripping from this, if there is, isolate the heating source and call a plumber. What are you using to heat the water at the moment? the boiler or the Immersion heater? does this dripping sound correspond with the time the boiler or immersion is switched on?

 

[MarkMas]

Thanks for all the info. Yes indeed, it's a pressurized system so no header tank. No separate pressure vessel as far as I can see. And yes, I have found my tundish now, and it is dripping - quite quietly and fairly fast - possibly because I fiddled with the knob at the top of that pipe. But last night it was much louder! Can't see any connection with particular amounts of water or boiler use. I will call a plumber.

 

[jasst]

Glad I was able to help, never thought I'd be able to work from home in my job! currently enduring enforced 6 week lay off, due to broken ankle, so at least I don't feel quite so useless now.

 

[midlifecrisis]

I think a few of us have learnt a few things here too...never knew what a tundish was or did. Thanks

 

[conaero]

Nope, me neither, well done Jasst.

 

[MarkMas]

Plumber says that diaphragm in 2-year-old pressure cylinder (turns out I do have one) has probably failed, and cylinder needs to be replaced. I think Jasst could build a new business around remote plumbing consultancy! Thank you!

 

[jasst]

Two years is a bit quick for that to fail, on top of the pressure vessel (or side, depending which way its been fitted) is a schraeder valve, with a tyre pressure gauge you can check the pressure, it should be 1 or 1.5 bar (should be on a label on the vessel), you can top this up with a suitable pump, if it is rapidly losing pressure then yes the diaphragm has gone.