Shower pump not delivering

[scooby_doo]

We have a problem with a showeroom in which the pump now no longer delivers supply to an electic shower unit or a monobloc basin tap.
Back in January, after a week in the sun, we returned to an icy UK (-4 c), to find not a drop of water from the tap.
My first thought was a frozen pipe, but when I got to investigate, some 12 hrs later, the tap flowed & we thought all was good.
However, some hours later again, a further try was fruitless.
I checked the supply pipes - nothing frozen; power to pump good & no other apparent cause for the failure.
This showeroom was created c. 2005, with a Mira PP2 pump supplying CW only from the cistern, to an Aquatronic +1 electric shower. Cold to the basin & loo direct from the cistern & hot via a small boiler setup.
In 2020, I remodelled the space & extended the pumped supply to a monobloc mixer, with a diversion through a Stiebel Elton heater unit.
In the past 5+ years, this setup has never failed to supply - even after the reworking.
To date, I've stripped the pump (no fault found); fitted an air vent in the loop from the pump over & down to the outlets (no effect).
I've also jury rigged a pipe from the pump outlet into a bucket - I can get the pump to start by using a magnet to raise the float - but this is not continuous.
I have also removed the shower unit & tap tails to establish that there is a good flow through the pump that just will not kick in.
For reference, flow at the 15mm outlet to the shower unit is 7.2 l/m @ 2050mm below the cistern; flow from the flexible below the tap is 6 l/m @ 3350 below the cistern.
The heads concerned are: cistern/pump - 600mm; pump/showerhead - 1850mm: pump/tap - 3000mm.
Pump & cistern are directly over the room & pipe runs are minimal.
The takeaway is that:- I know the pump works; it had worked for many years & now, for some unexplained reason, we now have no supply to the room below & I'm baffled.
The only factor that might impact is the minimal head of the pump below the cistern.
I can't think of any other cause & I'm hoping that you good folks may be able to point me to a possible cause &/or fix.
Many thanks.

 

[Madrab]

Well I guess the 2 glaring points here are 1) an electric shower shouldn't be fed from a pump, it's designed to be mains fed. That being said I have seen electric showers pumped before now and even fed from a gravity supply, albeit the cistern was 8 odd m above but they've always ended up having problems 2) A PP2 pump is a shower pump was never designed to supply anything but a shower and certainly not single supplies.

Obviously if it has been working up till now then it will and does run like that and as suggested it wouldn't be the first time I've seen shower pumps used like this. If you can trigger the pump by manually activating the flow switches then it has to be there that's the problem, the inline switches may be worn or restricted. You can still get the mag float service packs I believe

 

[scooby_doo]

Rob - many thanks for your response & observations. As the saying goes "if it ain't broke, don't fix it" - it was 'bodged' 20 yrs ago by some plumber(?) - but it worked!
I'm beginning to think that it may be an electrical issue - but I've followed up Mira's fault diagnosis: motor windings are good; relay resistance good; actuating the mag float shows the sensor is good. So I'm inclined to agree that it's the float that is just not performing, so I'll track down a replacement.
Cheers