overflowing cisterns

[fadetogrey]

Hi all,new user hoping for some help with what may or may not be a problem.My home was built 6 years ago and recently I noticed when the washing machine is filling or when the shower is being used all the toilet cisterns (2 upstairs,one down) are filling even though they are full and then run to overflow.
This lasts until the washing machine stops filling or in the case of the shower when the shower stops being used then the cisterns also stop filling.Im wondering is there some sort of valve leaking past and is it a job for a professional,thanks for any input...

 

[longdogs]

Sounds like a pressure problem. I don't know what type of fill valves you have in your toilets but when the washing machine is filling, the pressure at the toilet valve reduces slightly allowing the water to pass through and over-fill. It might be that the diaphrams are weak in the valve.

You could try fitting non-return valves.