got a problem with a ferrolli optimax 25c. there is no heating when the themostat switches on.
hot water works fine.
there are no error codes.
the boiler operates normally if you put it into test mode. that is the raidators get nice and hot.
has anyone got any ideas as to what can be wrong?

yes its a room themostat, a honeywell cm67/61ng with a hc60ng relay box.
i have checked and it is switching on demand across terminals A and B if i remememer correct. and i have traced the wireing for continuity all the way up to the input on the boilers circuit board. ive even used a wire jumper to simulate the relay switching in a circuit, so im at a loss

so if the switching of the thermostat is detectable at the boilers circuit board and the boiler can be "forced" to run using the test mode what else could be wrong that maybe test mode ignores?