Presumably you have tested the water flow without the shower head attached? Gainsborough shower heads will give the appearance of a trickle flow when the rubber nozzle plate distorts.
It runs hot and cold because the water cant flow through at a fast enough pace. Your shower is chucking its standard 9Kw or whatever of heat into water that cant get out quick enough so it overheats [hot water] and cuts the power off [cold water] as a safety precaution then resets itself and the cycle begins again
Have you turned the water off lately and not turned it back on properly
Do you live in a hard water area
Was the onset of this problem sudden or gradual
Find out if the restriction is before, during or after the shower unit to point you to the cause
Sorry to resurect this old post but I did a google search trying to work out whats wrong with my shower and found this
Exactly the same problem, its not the shower head, or the hose thingy bit?? Mine is a Gainsborough 10.5kw and isn't a year old yet (having had the first one replaced as the heating element went)
We do live in a hard water area, the water is switched on fully and we checked the filter so its not that
Just wondering if this was ever resloved and if anyone knows where we can look next
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