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.
--
Cheers,
Set Square
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