18 month old shower now hunting/pulsing.

[Isambard]

Searched similar posts but they mostly relate to newly installed items. Our Mulga thermostatic shower, fitted last year and fed by a Stuart Turner pump, was absolutely fine when we moved in five months ago, then last month began occasionally hunting on startup before settling into normal flow after a few seconds. Now it continuously hunts on all temp settings except hot, which runs normally.

Downstairs shower works just fine on all temp settings, fed by the same HW cylinder & CW cistern via the same Stuart Turner pump, so pump and feeds to it seem okay.

Tried flushing potential air lock, taking shower head off and hanging hose but neither has worked. With pump switched off, cold water is at a trickle, hot water at expected gravity pressure.

Is it possible for the shower's cold inlet to be blocked or clogged, downstream of the pump HP outlet and cause hunting? I'm leaning towards a faulty or blocked shower unit but wanted thoughts before I start reverse engineering everything.

 

[oldbuffer]

The shower has filters on each inlet. Worth isolating the hot and cold supplies, undoing the two nuts holding the mixer to the pipes in the wall, and inspecting / cleaning the filters. Don't know, but there may also be non-return valves in the inlets. If so, also worth checking they are working freely and easily.