Hi, I own an Ideal ICOS He24 Combi boiler system. One morning about a month ago I realised the boiler had stopped functioning and was displaying the error code L9 or sometimes H9 depending on whether I attempted to start the central heating or hot water. I looked in the manual and found out the codes meant: "H9/L9 - Heat Exchanger Overheat - advised to check the system is filled and vented and the thermistor values are correct and also inspect heat exchanger for blockage or damage." I called out an engineer who took a look at the boiler and told me that a new error code was showing (which it was, but I had not seen this before his visit). The new error code was LE/HE. The engineer read the manual and found that this indicated a PCB fault and decided that another PCB should be ordered. We did that and he turned up a couple of days later and replaced the PCB but unfortunately the boiler would still not work. Now, the boiler starts up when it is switched on and the fan seems to increase in speed while the pressure needle (which whilst stationary is at 1.5 bar) jumps around along with loud clunks from inside the system. This lasts perhaps a minute before the boiler gives up and shuts down, the burner light flashing. Does anybody have any idea what the problem might be? I've now spent £1000 on engineers bills and still no-one has diagnosed the problem- the last suggestion being to get a new boiler. This has now been going on close to a month and I don't seem to be any closer to knowing what is wrong. It's also getting colder and we have no hot water and are having to sleep in our clothes! Any ideas would be appreciated.