First of all, thanks Bob for all the excellent information. I did
some investigating last night, and...

[This is long, and my description are probably a bit cr&p...]

"Bob Mannix" wrote in message ...

-8- for brevity -8-

It's possible the thermostat is OK but the element has a lot of limescale on

that was my first thought, but then I understand that Edinburgh is a
particularly soft water area, and I understnad that the cylinder is
only around 3 years old, it having been installed when the loft
conversion was done.

it (causing localised "kettling"). The thermostat will look something like:

http://www.diy.com/bq/product/product.jhtml?PRODID=176966

Excellent, thanks - I couldn't see that last night (the cylinder is
accessed through a small cupboard door), but now I know where and what
I'm looking for.

at the top and the long brass tube extends to suit the heater that's fitted
(so get one the same length!). The dial on top sets the temperature.

-8- snip elictrical connection details -8-

Winding it up and down and retrying is a sensible thing to do first.

Will try this.

Another thing one could do is to insert an immersion heater timer in the
circuit - at least then you can ensure it's not on from 10.00pm to 6.00am,
for example. Remember, the last piece of cable that runs to the actual
cylinder heater should be heat-resistant flex.

Well, following my investigations of pipe routing last night, I
believe I hve worked out what's going on. I'll try to describe it as
best I can, but it's a bit of a jumble...

The boiler is a Vokera Mynute 20SE and is not, as I had been told by
the previous owner, a combi. It does, however, have the ability to
run a hot water cylinder using either a 'Y' or 'S' configuration (I
don't entirely understand these terms, but I think I have a rough idea
from the manual' layout diagrams); from the piping layout it appears
that our boiler is heating water using the 'S' configuration - at
least, there are two motorised valves in the cupboard - with the
downstairs hall radiator as the bypass. I assume from the layout
diagram in the boiler manual that this means the boiler can heat the
radiators or the hot water cylinder independantly.

There are just three pipes leading to the boiler - I assume these are
the inflow, outflow and gas.

There appear to be three pipes leading to the cylinder, although I
presume there's one more I can't see - I assume these are the mains
input, hot water output and boiler system inflow/outflow.

The pipes adjacent to the hot water cylinder appear to originate from
the boiler (at least, two disappear under the floor, roughly towards
the boiler, and were warm when I was working last night. One (I
assume boiler outflow) appears to feed the cylinder via one motorised
valve, has a pipe leading off (I assume) to the bypass and feeds what
appears to be the rest of the heating system via the other valve; it
is also connected to the mains water via a flexible hose. The other
(I assume the boiler inflow) appears to feed the cylinder and the two
heating pipes. Of course, they also appear to be connected in random
ways to each other, but the heating works, so I'll ignore that!

There were two hand taps in the cupboard: one is on what I assume is
the boiler inflow pipe, just next to where it exits the hot water
cylinder; the other was on the boiler outflow pipe, above the joint
that leads to the T-joint to which both motor valves are attached.
Opening each of these about a half turn appears to have given us hot
water this morning despite the 'hot water' switch (electrical
immersion heater) being turned off.

So I assume the electric immersion heater is a backup system to the
boiler, which now *appears* to be working.

-8- snip details of replacing immersion heater and/or hot water
cylinder -8-

I hope replacement won't be necessary, at least for the moment. Will
the kettling cause lots of damage, or is it mostly just an auditory
annoyance?

Thanks again for all the helpful advice - Adam...