Recently had installed a grundfos watermill 2 bar pump and triton satelite digital mixer shower.
Everything has been done as per instructions with pump situated on floor of airing cupboard below the HW cylinder (indirect type). HW is taken from top of tank via a surrey valve so it effectively has its own supply.
The cold water pressure is great - just as I hoped a "power shower" would be. - however the pressure from the hot water is really poor. It sounds like it simply is not getting the hot water from the cylinder to the pump quickly enough as when only cold water is asker for the pump runs smooth and quiet. When you turn on hot water, the pump is noisy and shower fluctuates (with significantly less pressure than the ancient old electric shower I replaced in the first place.)
The cold water storage tank in loft could be lifted about 18 inches or so - would this make any noticible difference to how quickly is forces the HW out of the cylinder into the pump?
Oddly enough the HW pressure to the taps in the bathroom seem OK.
Or could the triton digital mixer (which is in loft) be restricting the flow somehow of hot water - the pressure and temp both fluctuate in a very regular pattern as if it is opening and closing a thermostatic valve or something
Any help appreciated - £800 for supply & install and 3 visits from plumbers and still have a shower we can use 4 months later!!
You haven't said where the cold water supply to the pump feeds from. Unless it comes from the header tank in the loft then that might be the cause of your problem.
Has anyone checked the inline filters fitted to the pump and shower valve? Debris can easily be drawn from the cylinder on a new installation and as the symptoms you describe are very similar it might the cause.
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