My Valient turbo max plus 824e is not firing up for heating radiators. Hot water is o.k. The room thermostat controll setting does not activate it. Is there an over ride to switch the boiler on. Would the timer control setting be the cause? Where can I find a link for a schematic. N.B. I have an understanding of T.V. and domestic appliance repairs. Help please.

Keith, November 2022

I wonder if it's a failed diverter valve (possibly just the motor/actuator). There should be a little lever in the diverter actuator that moves when the motor drives it. This in turn turns on the boiler and pump, I think. You can usually move the lever by hand and slot it into a locking position. That'd suggest a bit more definitely where to start looking.
There should be some stuff on YouTube about checking diverter valves.

Rjffj, November 2022