Christian McArdle wrote:
from which I deduce that the boiler /needs/ a stat and is low
volatge ?

Nope. You may deduce no such thing from that statement.

P.S. A bimetallic thermostat REQUIRES a 230V connection, or it will
work very badly...

A "volt-free contact" requirement from the boiler will mean that you
need some sort of electronic stat with built in batteries. Almost all
programmable (and many electronic) thermostats meet this requirement.

Old style bimetallic thermostats have a 3 terminal connection and use
230V power from the programmer to run a tiny heater that gives much
more accurate control to the bimetallic strip. This heater will not
function as intended on a low voltage supply and the temperature
stability will be all over the place.

Christian.

so I will have to up the budget by £13 and buy a battery powered digital stat
/if/ the boiler is compatible with such a device ?

thanks for your continuing input, how about the cable run in relation to the regs ?