glow worn boiler says f9 on display and will not work?

water pressure may be too low, try topping up. water pressure switch may be blocked, also on some early models the overheat stat, which has a manual re-set causes the same fault.

Ian
March 2010

F9 - Pressure -

water pressure connector loose/ unconnected/ faulty or wires trapped.
water pressure sensor faulty.
pump ceased/ faulty

http://www.glow-worm.co.uk/products/pdf/current/Ultracom_cxi_installation_manual.pdf

- page 46

hope this helps

Gaz
March 2010