Shower pump stops and starts when not asked for water

[intheend]

I have a shower pump that was stopping and starting constantly and i mean when the shower is off. So i assumed faulty flow switch and replaced the pump, few days later the new pump started doing the same. Both hot and cold from the pump have an air vent fitted and when i vent the air it stops the pump coming on intermittently. I have to unscrew the top of the air vent to release the air would fitting an automatic air vent solve my problem and where could the air be coming from. Also if i shake the pipework around the pump it starts for a second then stops. This one's a tester as i have exactly the same setup next to it powering a 2nd shower and that works fine.
HELP!!!!


EDIT : Just worked out that it has AAV's already fitted and its the screwtop type. Now the screws are closed down not allowing the air to escape and the pipework is obviously dragging air from somewhere (no leaks been through with fine tooth comb) am i ok to open the screws and just leave them open as i think the impellers movement in the water is causing the formation of air in the system. And why is called an automatic air vent if the air cant escape when you close the bleed screws down lol. They are honeywell AAV's and they recommend to shut the bleed screws after initial bleeding of the sytem. But really am i ok just to leave them open surely they wont leak unless debris gets trapped under the air break!!!

 

[Technotim]

Is the pump fitted in the loft ? if it is then that is why there is air vents.
Make and model of pump would be helpful.

With out knowing this I can only guess.

Your air is coming from the hot water cylinder and poss the cold water tank especially if you have a small storage of water.

you should have an air free supply to the hot side of the pump eg Surrey Flange, Essex or the best one Techflange.
if the pump is in the loft plumb in an anti-gravity loop.

the air in the pump needs to be rectified but is not the problem.

The issue you have buy the sound of it is something called hunting where the water in the pipework is moving back and forth this is common with long pipe runs you will find that the hot side is the side that is effected normally.
test by letting the pump get into that state where it is on off then isolate the hot side of the pump if this stops it, then fit a non return valve on the outlet side of the pump.

Untitled

• Technotim
• 13 Jun 2008
• 3

This is a Anti-Gravity Loop With Techflange

 

[intheend]

Ive got a couple of 22mm double check valves should i just fit them and see what happens. And yes it is in the loft. The thing that is driving me crazy is that there are two shower pumps fitted side by both being fed by seperate CW cisterns and seperate hot feeds from 2 of the 3 cylinders in the property. One of the pumps is absoloutely fine on exactly the same setup (both come out from a surrey flange). Ive opened the air vents and that has stopped the problem but it still overuns a little like 4 pumps after shower is off then it stops. Think ill fit the check valves and ill post the results.

Pump is a grundfoss 1.5 bar but not sure on the model. The storage of water is more than sufficient definately over a hundred litres in each tank and they have a good head above approx 1.5m.

 

[Technotim]

I would just on the hot first as that is the normal suspect, it will not hurt to fit both but i do not think it is the cold as you have a loft installation.