Why is my electric shower fluctating hot/cold when I turn pressure up?

Hi Alice, I'm not sure electricians could be blamed for this, looks like the flow of water and indeed pressure are low, an instant heating unit is not designed to increase water flow or pressure. An alternative is replacing the unit with a pumped shower, for instance Mira Elite 9.8 kw silent pumped electric shower or anything similar. Another option would be installing a shower pump, I would recommend Stuart Turner, if the feed to your shower is coming from a vented cylinder, or a booster pump if on mains. Your best bet would be having the shower assessed by a plumber then you can see what options available. Hope it helps, cheers.

There could be a few issues here, is it fed by the mains ? 1st we need to check the cable is sufficient for the kw shower you have, otherwise it could be a thermostat problem with the shower, it could be poor flow so maybe something as simple as a blocked filter on the inlet pipe, I’ve seen plumbers put too much sealant on their pipe connectors before now leading to a blocked gauze filter, also try it with the shower hose disconnected, a blockage after the shower unit can cause problems. Either way might be worth finding a plumber that does electrical work also to take a look.

This sounds very odd as the hot to cold issue you are having sounds more consistent with a low pressure / flow rate problem rather than when the latter is increased. That said, when on eco it is likely that it is only using 1 element. You may not have high enough water pressure to run this shower effectively, or possibly a blockage of the inlet filter. Either way it is likely there is some restriction in the throughput of water. Make sure you are using the original spray set & hose which came with the unit, check for any flow restrictor which may be fitted in the hand set & try without. Also try removing the head & see if it still does it with just the hose. It sounds like the high limit thermostat is activating which is likely due to inadequate flow rate. Hope that helps.