Glowboiler & 3P.V fault.

[mkflow]

hi,
I have a faulty 3 port dirvetor valve, when switch c/h on h/w gets hot so checed valve motor has packed up not switch across.
however fault on boiler reads f4? anyone know or have an idea why.
the system is a y plan open vented with cylinder in airing cupbard and boiler in kitchen. boiler is a glowworm about 2 years old. would f4 mean overheating as faulty 3.p.v


many thanks