In message , roy atherton
writes
The family has noticed major interference on the TV when watching digital
channels at certain times when the central heating boiler is on. By trial
and error, I have discovered that the diverter valve is making a ticking
noise when both the central heating and hot water are on. This ticking (Hope
it is not sparking) is causing the interference, and it does not occur with
just heating or just water heating.
I could get by, adjusting the hot water timer to times when the heat is not
on - but should I be getting it replaced?
Is the replacement just an electric motor which I could replace myself, or
are the motor and the valve integral, so I will need a plumber to drain the
system and do a full replacement?

It sounds more like a faulty microswitch in the actuator head

You can buy the heads separately, or if you're feeling adventurous,
replace the (probably) middle microswitch which will prolly cost under
£2
--
geoff