The system was not power flushed when the boiler was installed.
TIA
Was that because you have a nupty installer who did the job for just £350 but not to include any power flush? [ Not wiring the pump to the boiler implies a non registered East European nupty ]
Or did you refuse to pay him the extra to power flush?
Or was it clean anyway?
In any case the problem seems to be possibly just setting the boiler up correctly although its off those coming under the warrantee did not manage that.
You dont say it but it seems the boiler is not even running the pump on a demand for CH.
It seems odd that the warrantee engineers seem to have all three left without solving the problem!
Tony