Vaillant 831 PCB issue?

The boiler is very intermittent when it comes to putting the Rads on, the hot water is fine and has no problems.
The thermostat is working and is sending 240v/240v in and out of the board. When I push the temp up on the thermostat the boiler will try to turn on but fails, however it will turn on when it feels like it..
There is a enough pressure in there cause when it works it works...

Does this sound like a PCB issue ??