Mysterious behaviour of pump

cleeve · Jan 4, 2013

I have a Stuart Turner Monsoon pump to supply hot and cold water to an upstairs sink, bath and shower. It behaved perfectly for years until I recently changed the sink tap to a monobloc single lever tap. At first, I thought the problem was a sticky valve in the tap, but now I'm convinced that although this tap initiates the strange behaviour I am more puzzled by what the pump is doing.

If I turn the lever tap on quickly there is no problem but if I turn it on slowly the tap spits out half a teaspoon of water and then nothing: the pump fails to start (i.e silent). If I leave the tap on the pump will eventually start up after a delay of about 10 seconds. So, what is happening during those 10 seconds if no water is flowing? What subsequently causes the pump to start?

Once the sytem has entered this "delay" mode turning the tap off and on makes no difference and it eventually starts after 10 seconds (assuming it's turned back on). I ruled out a sticky valve in the tap as, after it has entered this "delay" period, turning other taps in the bathroom on and off makes no difference, the pump still refuses to start until the 10 second delay has expired.

The bath taps are separate and rotary so these always turn on 'slowly' but I never have the problem initiated by the bath taps or the shower (also rotary valve). Consequently, I'm convinced the lever tap causes the strange behaviour but I'm not really concerned by that. I thought that the pump switched on as a result of water flowing past the flow-switches so I'd like to know what is going on in the pump during this silent 10 second delay and what causes it to start?

Howsie · Jan 4, 2013

Have you tried Stuart Turner technical support?

Avatar · Jan 5, 2013

Are you sure that this is happening at none of the other outlets - even to a degree?

It sounds like the flow switch but hard to say without an examination.

Sometime when you do work on the system damage can occur and for old fittings it can be the 'death toll' that finishes them off.

This happens frequently where I live in the south east as limescale knackers everything down here!

stevetheplumber · Jan 5, 2013

Sound like the tap doesnt flow enough to trip the flow switch not clear if pump starts normally from the other outlets ?waterways are very small in monoblock taps
other thought what happens if you open the monoblock fully turned to hot or cold it could be the crossflow of water causing the flow to drop which could be a problem as NON RETURN VALVES are very restrictive of flow
WAS IT A CHEEPY MIXER FROM A SHED OR EBAY ?

cleeve · Jan 5, 2013

Answers to two questions:
1. Yes, it does happen on the shower but EXTREMELY rare (twice in 3 months) and never during the first turn-on: only if I turn it back on just 2 or 3 minutes after turning it off. Whereas with the monobloc it's predictable and will happen every time with a slow turn on. I also live in the lime-scaled South East. But if it's a sticky flow-valve wouldn't one of them (hot or cold) switch on even if the other is stuck?

2. Having the monobloc on full hot or full cold or half way makes no difference to whether or not the pump starts.
Yes, it was a cheap plastic valve tap from Ebay. I accept that the tap is bad and if I could find the right socket set to remove the retaining nut on the valve I would swap it out.

I'm now thinking that the short burst of water from the monobloc with all its shoddy plastic parts and narrow waterways causes a flow valve in the pump to bounce. However, it's unlikely to affect both hot and cold valves simultaneously so I still don't understand what causes it to restart after 10 seconds of no movement - unless the pump has an electronic delay circuit.