For once this is my problem rather than sons or daughter.

Our central heating appears to be a basic S-type system with a Vaillent
Ecotec Plus 428 boiler, Siemens RWB2E timeswitch and RCR10 wireless room
stat. 2 Zone valves, one for CH, one or hot water. All installed by a
local company about 10 years ago.

Because of my persistent bad back, I don't feel safe climbing into the
airing cupboard and measuring voltages after taking covers off the boxes
there.
I have reset and checked the 2 controllers and all lights come on as
expected as dials are turned.

For about 5 days now the heating has been staying on all night. I've
been looking at the diywiki site and can't see how, with the stat and
timeswitch set to OFF, the system can be running. I can't believe that
both timeswitch and stat could have both failed at the same time.

Is there something I'm missing?
--
Bill