Check Non-Return Valve and Water Being Pushed Back into the Header Tank

[camberley_help]

Hi

We have an electric immersion heater (no central heating) and a few weeks ago a plumber installed a new shower and put the shower, basin & bath cold all on mains pressure.
We have mixer taps on everything.

We are now experiencing hot water being pushed back into the header (expansion) tank and causing water to leak outside via the outlet.

I suspect I need to fit non return valves but my question is … do I really have to fit 1 on the basin (hot) and 1 on the bath (hot) as this will be a nightmare.

I have noticed the immersion heater has 2 pipes at the top .. 1 going to the header (expansion) tank and another that feeds only the basin & bath hot tap

Can I not just put an inline Check valve here .. as its only feeding the 2 hot taps and water should only flow 1 way... it seems to me the same as putting a valve at the end of each tap.

The vent/expansion pipe will remain 'as is'


Thanks