We have a Stuart Turner Showermate 1.5 bar twin pump that feeds our shower. The water temperature is controlled by a Mira Excel thermostatic cartridge in the shower.
The pump is 8 years old. The MIRA cartridge is 3 years old.
When the shower hasn't been used for a while, when it is turned on we get a trickle of water for up to 30 seconds before the flow starts properly. Sub sequent turn-ons happen much quicker. I have checked the mesh filters on t he pump inlets and they are both clean.
Any suggestions please for what may be at fault?