Bosch Worcester 14/19CBI Installation And Servicing Instructions page 39

Delivered primary water
Check thermister
Move control knob to lower
temperature always too hot. sensor/heat conductive
Replace control board.
setting.
(Over 85°C) paste.
Such a fault is likely to be caused
by one or more of the following:
Low gas pressure
Delivered primary water
temperature appears too Partially blocked flue
Partially blocked heat exchanger
low with control knob set to
Blocked/dirty burner
maximum.
Gas valve sticking
(Less than 75°C)
Control board fault
Faulty themister
39