Geo wrote:
Came back (from B&Q) yesterday morning and noticed fairly load bursts of LF hum
at regular intervals - put it down to next door neighbour doing some arc welding
in his garage. Then went upstairs to bathroom and nearly wet the floor when the
LOUD 50 Hz buzz went off behind me. The bath was a mess of sprayed water and
black carbon dust and there was a continuous trickle of water from the base of
the Mira Event Power Shower.
Went to the bedroom to remove power - the electrician had not thought to provide
an isolating switch so had to find a screwdriver to lever the fuse out of the
spur.
Removed shower casing and discovered motor too hot to touch, carbon dust spread
around, and water coming out of top of pump case. Had wife make temporary fuse
connection so I could see what was happening - motor not turning but powered up
even although water control was in off position and microswitch contacts open.
Violent arcing from brushes.

So turned off hot and cold water and went back to B&Q (40 miles) to buy some
press-fit isolation valves - the plumber had not bothered to fit any. (See
other thread about HBP pipe and Speedfit).

The shower was used the previous evening at about 11pm and operated normally. We
left the house about 9:30 am and returned about 11:15. The motor has a Klixxon
thermal fuse (110 deg C) which was opeating after about 3-5 seconds then
resetting a few minutes later. The temperature reached had melted the impeller
within the pump and caused other damage.

PCB checks out working on bench (Triac, diac, varable pot) and the microswitch
works normally. The microswitch does not remove power but is in the gate circuit
of the triac. Putting a variable resitor across the microswitch I found that
about 30k was sufficient to switch the Triac on - so possible a combination of
carbon dust and moisture /could/ have started the destruction process.
The microswitch was protected with a rubber cover and appeared clean enough.
With the shower turned off the outlet is blocked to the pump would have been
under a strain.

Checked resistance between adjacent armature segments and found one place giving
high reading (about 32 ohms instead of about 4). Not sure if this could have
burnt out once the pump jammed or was the initial cause of the motor stopping
and overheating. There are score marks in the pump casing which would indicate
that there was rotation when the failure started.

Still puzzled that the thing started by itself - suspected mains surge had blown
triac but it is rated 600V and the PCB still works.

13 years is not bad but I would have preferred a more dignified death.

Pictures of damage he-
http://www.flickr.com/photos/1362986...7624607532432/


just another reason not to use pumped water supplies really.

I know its a substantial investment, but mains pressure water everywhere
is a far nicer solution.