"Set Square" wrote in message
...
In an earlier contribution to this discussion,
RichardS noaccess@invalid wrote:

Couple of weeks ago I got a phone call from our tenant who mentioned
that there was no hot water - the flat has electric only, and all hot
water provided by an immersion heater in a direct tank.

They'd managed to leave the immersion switched on for about a day,
and it had not only heated the 120l tank, but the large cold storage
tank above it (I estimate it must be 250 or 300l at least) to a
rather scary temperature. After that, they said it didn't do any
better than lukewarm, and then packed up altogether.

Well, after spending couple of weeks phoning him to get access to the
flat (suspect he'd been avoiding my calls, he owed us rent....) and
sorted the problem out.

I'd been idly speculating upon what the problem might have been whilst
waiting to do the job, perhaps the thermostat had packed up, etc etc.
Heater was open circuit when tested, so drained the tank down and
whacked in a replacement, no problems.

But, can anyone spot what could have been the problem with the
heater....

http://www.olifant.co.uk/Olifant/Pub...ks/RSAN-62XF2E


The immersion heater is now connected via a timer...!!!


Look like several problems to me.

1. Vent pipe dipping into water in header - thus setting up a
thermo-syphon
system which heated up the header tank
2. Immersion element over-heated and bent until it touched the thermostat.
The stat was then driven by the element rather than the water temperature,
and cut out prematurely - providing only tepid water
3. Element finally failed altogether

If I'm right about (1), you'll need to fix this, or the problem will
recur.


Hmm, thanks, I hadn't considered this. I'll check it when I'm back there
next week (there's nothing like a simple job for throwing up all sorts of
nasties that need to be put right, is there!).

I'm not entirely sure that the vent pipe is dipping into the header though
because when I drained the tank this would have surely either 1) siphoned
water out of the header, or 2) drained the header to the depth of the vent
pipe, and I didn't hear the header valve opening to replenish the level. I
had thought that in this case the header heated up simply through conduction
and convenctive currents set up within the feeder pipe to the HW tank.

Still, the timer will go a long way to preventing future occurrence, because
it's set to heat the tank in the morning, and they are unlikely to get
through an entire tank in the day (electric shower used far more than the
bath).

--
Richard Sampson

email me at
richard at olifant d-ot co do-t uk