Worcester 24SiII Installation And Servicing Instructions page 41

No
Is the boiler in a very
cold environment (less
than 5°C)?
Yes
Boiler is running in
"Autofrost stat" mode.
See Section 17.
Hot water
temperature always
too hot during a
demand (not
regulating).
Water flow
temperature very low
(with all knobs set at
maximum).
Increase
No
potentiometer to
allow more gas in CH
mode.
Replace control board.
Note: A damp board
could cause this fault.
Hot water sensor
could be off or poorly
fixed to pipe.
Repair or replace.
No
Does the problem
occur in CH mode
only?
Yes
Is the CH limit
potentiometer
(concealed behind
facia bottom panel)
set to maximum?
Yes
It is not possible to
easily isolate the fault.
The most likely causes
are control board (fail),
heat exchanger
(blocked) or
gas valve (sticking).
41
Could be
domestic hot
and cold pipes
crossed.
No
Remove multiway
connector from board
position ST16. Is the
resistance across
contacts 4 and 5 (blue
wires) below 60
ohms?
Yes
No
Check flow sensor:
with boiler cool,
slowly open a HW tap.
Does the boiler ignite
with a flow of about
3 l/min?
(Check using a
measuring jug and
stop watch i.e 500ml
in 10 sec.
Yes
Replace gas valve or
check wiring.
Turbine sticking or
seized.
Replace the turbine.