i have a gainsburgh 9.5scl shower and when you turn the shower on some water comes out of the shower head but more through the overflow at the back, does this mean we have lossed the pressure on the main unit
the pressure relif valve (prv) has operated. This is why you are seeing water coming from the 'overflow'
Check: Is the heater tank furred up with limescale?
If not you should be OK to replace the PRV device
and retry the shower.
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