Any idea as to what’s happening

[Camerontocher]

I think that your cold water feed could be blocked,your inlet will have a filter in it .
i am not willing to tell you what to do as it will invole electrics water shut off poss remove unit. etc.
please get plumber/sparky for your safety,

I’m a multi skilled maintenance engineer, so isolating the shower isn’t an issue and I’ll just turn the water mains off. As to plumbing I don’t have a clue hence why I’ve asked for advice on here first

 

[fowlerboi]

My first thought was blocked filter. I believe on the quartz (which is the shower you have) the 2 screws just after the brass elbow is the filter. Take this out and check to make sure its clean. I doubt you have the flushing piece which screws onto that position which you could use to test the water supply with but if you do then check that out as well.

Aqualisa 435918 electric pressure test adaptor

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If your supply is good and the inlet is clean then its time for a new engine. They aren't particularly expensive and are easy to fit.

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[Ben-gee]

Basics first.
Remove the shower head - if the shower now runs as normal, the head needs descaling/replacing.
If it still doesn’t run properly: remove the hose, if it now runs properly the hose needs replacing, it will have a hernia inside somewhere.
If this doesn’t resolve it; move onto th Ec filter as per fowlerboi.
Then it’s either remove unit and descale tank, or just replace unit.