A note on the Sunvic SZ 2301 zone
valve (2020-6-21).
The heating system for the East Island pool is somewhat complicated, and a few years
ago it developed an annoying fault that was difficult to trace.
The problem was that the oil boiler was always on, even when
no
heating services were required. The solution, for a long time,
was
simply to turn the boiler off at the thermostat, but the recent
installation of a high efficiency replacement unit prompted
investigation of the problem. It turned out to be due to a Sunvic
SZ
2301 zone valve controlling the feed to a radiator in the pool
corridor. This valve was issuing a boiler request even when
de-activated.
I contemplated buying a new valve
actuator head,
but these are stupidly expensive and have a reputation for
unreliability. So, instead, I dismantled the device to find
out
what was wrong (a security Torx TR10 screwdriver is required). It turns out that the boiler request
microswitch
is mounted on a couple of pathetically flimsy pins protruding from the
ABS back-plate. The switch is also loose on the pins for
about 2
mm of up-and-down movement, increasing the stress on the plastic.
I estimate that the valve might undergo someting in the
order of 1000 operations before shearing-off one of the pins, which would seem to
be in keeping with the user-reported MTBF of 2 to 3 years.
Buying an identical replacement for a
part designed
to fail is not a solution. Instead, I carefully marked the
location of the sheared-off pin with a centre punch and drilled a 2 mm
diameter hole in its place. I then secured the microswitch with
an
M2×0.4 screw (12mm long excluding head) and a nut. This arrangement does not allow
any
movement on the backplate and should last for many years. |