posted this 12 February 2018
As the pump works fine on one shower, it can't be a fault with the pump.
The monsoon pumps will generate the same flow and pressure through out their life as the parts don't normally wear. You could have a blocked filter on the pump of course but you would tend to get the problem at everything you are pumping to.
It's more likely that there is a blockage at the shower on the hot side (possibly filter) or the shower valve is faulty. Certainly it would point to the shower valve if you are unable to adjust the temperature correctly but you would have hoped that the
Aqualisa engineer would have found something wrong with it.
It could be that the cylinder isn't breathing correctly and the bottom of the cylinder is chalked up and restricting the flow of the cold water into the cylinder. If the Aqualisa shower uses a much higher volume of water than the other shower that could
explain why it is affected more. The way to test this would be to get a plastic bag, blow it up and tape it to the end of the vent pipe hanging over the cold water tank in the loft. If you run the shower and the air is evacuated from the bag then it tells
us the cylinder is pulling air down the vent pipe due to a blocked cylinder.