Update- son has just checked

the valves he has are two open shut valves (both appear to be working)
not y valves.

The thermostat downstairs seems to open and shut the valve but it
doesn't trigger the boiler and pump on.

The honeywell room thermostat in the lounge has 2 x 2 (2 larger wires
which contain a red and a black in each) be he can't see where these
should connect in the airing cupboard.