I have an Ideal Isostar HE24 Boiler installed under the warmfront scheme. I have been experiencing a worsening problem. The hot water initially runs hot then runs to cold. If you really turn down the flow rate it heats up to hot. This means that the shower won't work and it takes an age to run a bath. There is no issue on central heating (I think - its not been used since April). I contacted Ideal and they want me to arrange an out of warranty call out at a cost of £275. I've seen a lot of discussions about faulty PCB's but Ideal say its probably a problem the domestic hot water thermistor or a valve. Any body any experience to share that could help me resolve this problem?