I have a similar problem to posting for Worcestor 24i on June 20th. I had this boiler installed a month ago. No problems initially but then noticed no hot water to shower & taps unless heating on as well: reset button kept flashing if I taps run without heating on. Then noticed flame on gas cooker dropped dramatically when heating on. Installation engineer came & checked but found no problem with boiler: tested gas meter & recorded that gas pressure immediately dropped to 1 when heating switched on, the reading then slowly rose to around 20 (not sure what units!). He suggested fault was with gas meter & named a possible faulty part (can't remember what). He said he could not check it as meter was suppplier's property & I should contact them. I will get him back to check items noted in June 20th similar posting but would this explain drop in gas pressure from gas meter & the effect the heating has on the cooker.
Also should I avoid using heating or cooking before problem fixed - installer is now on holiday for a few weeks & I need heat & food!!!
All advice welcome.