I have bought a house with a fairly old oil-fired central heating
system, which works well, so we're not planning to change it.

The only problem is that the system works by being on all the time,
maintaining a tank of hot water, and the only way of turning off the
room heating function is by turning down the thermostat in the hall.

This means that we have to wake up and turn up the thermostat at 5 in
the morning in order for the house to warm up again...

Is there any kind of timer control that could be used with this
system? I've always had gas central heating in the past, and each
system has come with a timer control, but there doesn't seem to be an
oil equivalent.

Can anybody help?

Many thanks.

Is there any kind of timer control that could be used with this
system?

Yes. You could use a programmable thermostat. This is a simple direct
replacement for the hall thermostat that also has a timer function.
Alternatively, install a proper programmer in the system. There isn't really
much difference between oil and gas central heating systems, except that oil
boilers take a bit longer to fire. The controls can be similar.

You will also want to check that your hot water cylinder has a thermostat on
it. If not (and I suspect not), you should upgrade the controls to include
one (as well as a timer, probably) to turn the boiler off when the hot water
doesn't need heating.

Christian.