Help!....no hot water this morning!

[doowot]

My Excell 80SP seemed to play up this morning. The central heating came on as usual, but when I tried to use the hot water, it just ran cold...I even left it running for several minutes. I then switched the setting to water only...still nothing!! I switched back to C/H mode and turned up the thermostat slightly, tried the hot water and Eureka! the hot water came gushing out!!
Ten minutes later I tried the hot tap....No hot water!!...but if I up the thermostat slightly to get the radiators going then turn the hot tap on...I get hot water!!!??
Something is amiss!!

Any advice please would be appreciated

 

[doowot]

Still having problems with my combi...it seems contract only covers faults if I have absolutely no hot water, so because I can get hot supply when my boiler is working for the c/h, I cant get a free callout!!!
Might be worth asking a local engineer for a quote!1 I'm sure its the diverter valve..this will be the third time in 11 years!!