Mira Escape pressure drops when increasing temperature

[craig05]

I've got a Mira Escape and just had the heater tank replaced. All works okay but when switched on the low flow light is on, pressure is very good when temperature is set to cold but as you turn the dial to get hotter the pressure drops. Get the dial round to get some warm/hot water out, the pressure is really bad. Issue is not with the shower head/hose. Any idea why?

 

[terryplumb]

That's the way electric showers work , reducing the flow of water makes the water hotter. So turning the temperature up is actually achieved by reducing the flow.

 

[craig05]

But the drop in pressure is so much more than before, plus before we never had the low flow light on. Previously the pressure change when increasing the temperature was marginal, now it is very significant. Something is not right as it is so different before the tank change.

 

[Johntheo5]

I think thats a thermostatic shower?, some work, I think my keeping one heater element on full power and only control the power level in the other one, don't know if thats how it works but assuming it is, then if it can turn the power to one element to 0kw and if its a 9kw shower, a flow rate of only 2.48LPM is sufficient to give a showering temp of 40C from (my) mains temp of 14C, if, for whatever reason, the power is 9kw, a flow rate of 4.96LPM is required, the more basic type where you can switch off the power to one element will generally give enough flow one element until the problem is sorted out.
If mains supplied could be pressure problem, if supplied from a header tank with its own integral pump, could be a pump problem, either way clean the shower filter.

can you measure the flow rate at its coldest setting?.

Had a quick look at the MIs, looks like the power selector selects either 0kw, or 4.5kw or 9.0kw "fixed" power (or 0,4.8 or 9.8kw). If so then the temperature selector switch should change the temperature setting and this in turn changes the flow rate to give the required temperature. So looks like mains pressure too low or (unlikely, since low flow LED a thermostat (if fitted) problem. If not already tried, put the top (power) selector) switch to II and see if you can get a comfortable showering temperature of 35/40C. but at a very low flowrate of 2.5/3.0LPM.