Valiant Ecotec 824e Firing Up When Not Needed

[iamlee2002]

Hi all, ive recently modernised the bathroom not finished yet though. I have noticed something unusual, If i flush the toilet or run the cold tap (opened fully so fast flow) when the water stops flowing (tap closed) the boiler fires up then i get a "pump over run" status code.
Any ideas? i havent crossed the piping, however i have put 2 isolating valvles near the boiler.

One on the 22mm coming out of boiler supplying hot water taps

Other is on 15mm cold feed after the boiler inlet.

Has anyone got any ideas?

Do you think when i close the tap then the water tries to push back into boiler and this causes it to try and disperse it?

any help will be greatly appreciated as im baffled

thanks in advance

 

[mickyg]

dead leg. put it in search.