Groaning/banging from water cylinder?

[Mike Smith]

Hi,

my daughter lives in a purpose built first floor flat (1980's)

She's been there 3 years. Recently, she has complained about alarmingly loud "bangs" and "groans" when she runs the hot tap to fill a bath. I've not heard the noises myself (yet).

She has a combination hot and cold water cylinder (Fortec is the name that comes to mind?) -- the small cold tank sits on top of the larger hot water tank - heating by immersion heater.

She is in a very hard water area and when she moved in I removed handfulls of limescale deposits from the cold water tank.

Mains pressure was good last time I checked (thumb over kitchen tap test...)

The immersion heater is on a timer and she says it is most likely switched on when the noises occur (not 100% certain though)

So, before I go and experience the noises myself, can anyone suggest what might be happening here and how I can determine, and hopefully fix, the cause of the noise?

Many thanks

p.s just found this link to a similar sort of cylinder:

[John Stumbles]

First off I'd check that the immersion thermostat is actually shutting off and not letting the heater boil the water. Asking her if the water is scalding would be a reasonable indication that that might be the problem.

If that seems OK I'd suspect air getting into the system which might be caused by the ball-float filling valve not filling the small header cistern properly.

[Mike Smith]

John,

thanks for the reply. |t looks as if you have pretty much hit the nail on the head. When I got there I found the water in the cold tank was warm to the touch and I could hear the immersion heater was active.

The element thermostat was set to 70 -- it was probably set that high to help in getting a full bath out of a small hot tank.

But my guess is the water was actually much hotter than 70, it certainly was scalding. So, I removed the thermostat and tested it in a jug of water from the kettle. An ohm-meter showed it was switching when placed in/taken out of the water from the kettle.

So, perhaps the thermostat is tempermental and "sticky"?

I've now switched it down to 55 degrees, and heard it switch off after a bit. I've left daughter with insturctions to keep a log of bangs and whistles to verify they only occur when the heating is on. (She also has instructions to switch the thing of at the isolator switch if it becomes too alarming).

Is this failure mode typical of immersion thermostats, or could the problem be that the immersion element is all scaled up, and "insulating" the thermostat from the real water temperature?

If the water continues to come out scalding, I guess the next logical steps are a new thermostat and, if that doesn't work, a new immersion element? (I hope not, as I have a pretty poor record of removing the damn things from corroded tanks...)

Thanks again

--Mike

[John]

Wouldn't it be great if we used CopperSlip on the threads of immersion heaters. After all, the thread is not the seal - the flange does the sealing. The trouble is that when they are fitted it is usually assumed they will be a permanent fit.