Worcester combi 24cdi - no hot water

After weeks of trying to identify when this intermitent fault occurs, I've finally narrowed it down.
When someone takes say a 10/15 minute shower, all is OK. If a 2nd person then takes a shower within 2 or 3 minutes then everyting is normally fine.
HOWEVER, if you wait 15/20 minutes after the 1st person has showered and you then try for a shower or run hot water tap, the DHW demand indicator light comes on BUT the Flame detection light stays off (& the boiler fails to ignite). If you then wait about 20/30 minutes everything is fine again.
Any ideas ??
I do have the Brit Gas cover but dont want to involve them unnecessarily. Armed with the info I have, do u think they could resolve now? (they couldnt find anything last time but have more info now).][/u]

If the hot water demand light always comes on with a demand yet the boiler doesnt start ignition process then you proberbly have a faulty pcb.

The DHW indicator light always comes on. But the secondary light (the flame detection light ) stays off, so the boiler doesnt come on. Funny it only happens in the way I described yesterday.
To temporarily get round it, I upped the temperature demand on the 'digistat' to start the Central heating. Once that fired the boiler I turned the C/H down again & then tried to get hot water again . It then worked OK.
Obviously I dont want to do this every time it happens.

When the boiler ignites it does not know where the heat is going to be used.

Either its not an ignition fault or you have been missled.

Best to let BG sort it out. I expect that as they did not see it fault they did not even check anything in the boiler.

First thing to see is if its actually an ignition failure. I think not as you did not say you had any lockout. May be a pcb fault or possibily a sensor.

Tony

No, there is no 'lock out' or flashing lights . As described it only happens about 15/30 mins after someone has had shower or run hot water for 10 mins or so.
The DHW demand light comes on when we turn on tap or shower but the flame light to the right stays off