Warm water, no HW pilot, but CH works?

I turned off the timers for a weekend whilst away, now the hot water is warm but wont get hot, and I think it's only warm because of the CH.

I have a Potterton Netaheat 10-16, and the pilot light doesn't come on when only HW is turned on. The thermostat on the boiler is set to max. The thermostat on HW tank is at 65 degrees. No settings have changed.

I live in a flat, so I think it's an unvented indirect non-gravity fed system (I'm a novice and been reading Collin's DIY so I could be wrong on the terminology). HW tank is sealed in insulated box and not easy to get to the top.

Any suggestions greatly appreciated! :)