Stuart Turner Monsoon Twin negative head 1.5Bar randomly switching on and off

[JamieH]

Situated under the bath to boost bath shower mixer taps.
Works perfectly fine with the taps on.
Randomly switches on and off for 5 seconds(ish) , 3-4 times an hour
Checked Pressure Vessel - flat - didn't hold cycle pump repressurisation so replaced it.
Checked with pressure gauge on new one - (0.9bar / 13 PSI)
Pump still randomly switched on/off.

Replaced NRV's with a pair from e-bay (Stuart Turner compatible)...
https://www.ebay.co.uk/itm/Shower-P...622107?hash=item4676ba27db:g:jVUAAOSwXGhahXpN
With those in place, pump randomly switched on/off EVERY MINUTE!!!???
Put the old ones back in so pump is back to cycling 3-4 times per hour.

Why would newer, 'springier' NRV's have worsened the problem?
(£9.99 rubbish?)

 

[Lower]

Check your bath mixer taps aren't leaking slightly.

 

[JamieH]

@Lower - There's a very slow drip coming from the tap.
It's slight but presumably a leak.
Wondering if it's worth making inner adjustments or replacing the 18 year old mixer set with a new product.

 

[Lower]

The pump has a pressure switch in it that determines when it turns on and off. When you turn the shower on, the pressure drops and the pump kicks in. When you turn the shower off the pressure goes back up and the pump switches off. The NRV's trap the pressure in the system and the pump stays off.

If you have a leaky mixer then the pressure is dropping slowly over time and that is why the pump periodically kicks in to build the pressure back up.

If the mixer is 18 years old i'd replace.