Last year I paid£600 for a heat exchange unit to be replaced on my IDEAL gas boiler. Less than 6 months later the boiler started making horrible banging noises and the engineer said the MAIN heat exchanger now needed replacing. He did the work at a cost of over £700 but now the boiler cuts out if I set the thermostat over 15 degrees and i only get a trickle of hot tap/bath water. The engineer says the boiler needs replacing as this is not an incorrect setting by him but a failure in the boiler that he cannot repair. He said this without even examining the unit. Am I being had over ????