Using 2 sources of water causes toilet to flush on own
When we use 2 sources of water at the same time (say a shower and a toilet) this will cause the downstairs toilet to flush on its own.(we can use the sink and flush a toilet downstairs and the upstairs toilet will flush, we can use different combinations, although the same combindation causes the same toilet to flush). We have a combi boiler in case this is the cause. We have lived here 5 years and this only just seems to have happened in the last few months (which coincided with a new washing machine that only uses cold water) any ideas?