Free boiler on government scheme

Last year while on benefits before I retired I had a boiler fitted under the government scheme. This weekend I had trouble with the water pump. when I contacted British Gas under the maintainence scheme I have. I was told by the engineer that when they fitted the boiler the system should have been flushed and it looks as though it was drained only. \I am now facing a bill to flush it of £600 being disabled I cannot afford it. Can anyone help with the contact for the government dept contact.