SIME SUPER 90 - Diverter Valve?

Hello all,
I have recently inherited a SIME SUPER 90 combination boiler in a house I moved into.

The boiler works fine but I have noticed that when I demand hot water the CH outlet pipe from the boiler also heats up considerably. If the boiler is in summer mode then the CH pump does not start and only the first 6 feet or so of the CH pipe heats up. If in winter mode (with time clock set to off) the CH pump runs and the rad nearest the boiler warms up. After the bath is run the nearest rad reaches approx 40degs C.

The diverter valve does operate - lifts and hits the micro switch to light boiler - but I am guessing that some of the heated water from the exchanger is leaking past the diverter valve and into the CH circuit? Damaged/decayed diaphram?

Please could someone with more experience than me agree/disagree with my diagnosis?

Regards

Daniel
August 2008