Boiler cuts out when shower turned on

Hi hope someone can help. Have had 2 plumbers in to look at a Maxol combi. Boiler cuts out whenever the shower is turned on and fault no 6 is shown. CH works fine, bath lukewarm while radiators are hot. Its just been looked at by an engineer who said there's nothing wrong with it. Previous plumber fitted an independent pressure tank . It worked for one night!! The system was recently power cleaned and was v sludgy but worked a treat after. Now this which means no showers or baths... what the heck is going on?

I had similar problem with my combo its to do with the temperature switch does yr temperature on boiler go sky high when u run hot water? Some plumbers r just useless! Yr best bet is get British gas out they do certain deals check online to see wht suits yrself.

I done the deal to sign up for their home cover where pay £99 to fix any problem then yr covered for £18 a month it's a bit steep compared to other home covers but it includes service each year

was it "power cleaned" with the boiler in situ? could be that some of the debris that was in the system is now blocking your plate heat exchanger. get your engineer to check it.