If you have a room thermostat then you are better having the boiler thermostat high and control the temperature with the room thermostat to the desired temperature that you want. If you have the boiler turned down low then it will take longer for the radiators to heat your property to the...
I know you don't want to call out an engineer, but the chances are it "could" be either a faulty part on the boiler, eg fan, pump or a faulty PCB.
If you're getting grief from the other half then maybe the problem would be solved quicker if you did.
It doesn't sound like its a water/circulation problem. With the E133 error I would say the gas valve may need adjusting. The co/co2 ratio may be out when in high fire (when hot tap on full) and works ok in low fire (running hot tap slow).
Get the installer back, or any other gas safe engineer