I have the above named combi boiler which has developed a problem with DHW heating, most notable when the shower is in operation, although it can be felt when the taps are run but to a lesser degree (Probably due to amount of flow/amount of body imersed). The water temperature drops off then picks up again in a continuous cycle. On observing the boiler it can be seen that the flame intensity reduces then intensifies, this ties in with the temperature fluctuations. The area I live in is generally thought to be soft water, so I'm not sure if a Heat Exchanger flush would be prudent? Any advice that relates to this type of defect/boiler is much appreciated, thank-you.