I have inherited a plumbing problem, and the main problem I have in solving it is that the pipework is inaccessible without ripping out a shower and a bath and two tiled floors so looking for some workarounds.
I have two showers powered by a Salamader RHP100. We recently replaced one bath shower combination with a shower enclosure and everything seemed to be working fine (which was a surprise as the original installation was problematic) but as we hit winter the shower pump refused to trigger.
I had done some flow tests and it suggested that the unassisted pressure was marginal for the pump. However, the shower next to the pump works 100% reliably, the one with 5m of piping is problematic.
In various researches, I noticed that more recent instructions for the pump suggested that the flow required was 1.5l/m for hot, or for cold or 3l/m for both, and that set my investigations on another path. I found the shower would trigger the pump if I turned the shower on and then set the shower thermostat (Grohe) towards cold.
So, by isolating the cold from the hot, or stopping the hot from flowing, it seems the pump will trigger, but when both hot and cold are on demand from the problem shower the pump does not trigger. (We can also start it by lowering the hand held shower down to the ground, which does imply a pressure issue).
I was also intrigued that the ambient temperature in the loft and therefore the water might play a part, given that the rest of the house is at the same temperature all year round, yet the "active" pipework is within the warm house.
My thought is, does this imply that there is some backflow issue, where the cold is balancing against the hot so that it does not flow when isolated the cold pressure is sufficient to overcome the pump pressure sensor?
If so, is it worth trying to put a one way valve in the hot water circuit as it is the only thing I can think of that I could alter from pipework that is accessible?