"DIYSOS" wrote in message
news
I'm fairly sure my model doesn't have the electrical cutout you describe,
didn't see anything on the HX pipes when I looked the other day*, plus it
doesn't have an electrical connection (;-).

Mine doesn't have an electrical _supply_, this is all driven off
the thermocouple. As I said, older ones don't have a thermocouple.

The flavour of cutout I was on the lookout for was something to turn off the
boiler if the (water) temperature overshoots it's set limit. I think this is
the thermal cutout you describe... according to the docs on baxi/partsarena,
the Medway Super had such an "energy cut-off device". For better or worse,
my model is too primative to have one of these.

Can't recall what my model is -- it's about 5 years old and does
have thermostatic control, and was the middle range of 3 which were
sold at the time. My much older one (which did overheat and self
destruct) was a Main Medina. The rather long 15mm pipe with lots
of elbows which used to feed gas to it had 1974 stamped on it IIRC,
but that could predate the Main water heaters as the house did have
an Ascot at some point (neighbour still had one when I moved in,
and I have a matching filled in flue hole in my outside wall in the
same place).

*I had the case open as I wanted to remove the HX to de-scale it, long
overdue after 20 years!. I followed my new-found instructions, undid the
unions and screws, but when it came to it the flue part of the HX is
immovably fixed into the wall-mounted flue housing - it really won't budge.

My recollection (hazy) is there are just a couple of screws holding
the top of the HX in place in the cabinet, and the flue connection
is just a slide fit. I suspect if it won't slide out, you won't be
able to take the thing off the wall. These units have all used the
same flue for decades -- if a unit dies, the new ones are all designed
to hang on the flues of the older versions, so you don't need to
replace the flue too.

So, all I can think of is wait until if/when it gets disconnected for
replumbing. Then, connect into cold in / hot out pipes and somehow run
descalant through the whole thing - flow sensors and all (do these contain a
rubber diaphram and are they the 'weakest link'?) These will also have to
survive 'Fernox' of similar, and anything else coming out of the radiators
if my mad plan actually happens.

I descaled my old one a few times in the bath. I used kettle
descaler and rather worryingly, the liquid came out bright
blue or green (I forget), but it didn't seem to do any harm.
The new one has internally coated teflon pipes IIRC, which
is supposed to reduce the need for descaling and I haven't
had to do it in 5 years -- flow rate still fine.

Wonder if you can still get spares for these things?

I suspect so. They were very popular and around for several
decades. They still do a couple of models, although one is
quite different (electrical with fanned flue).

--
Andrew Gabriel