Shower pump activated by hot water taps

Our shower pump turns on momentarily whenever a hot tap is operated in the kitchen or the bathroom. The pump runs for about half a second just after the tap is turned off. The pump/shower system is designed to switch on whenever the shower mixer valve is opened, so I assume this malfunction is something to do with a pressure drop in the water system. Can anyone suggest what I need to do to correct this problem please? Thanks. Trevor
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snipped-for-privacy@btinternet.com wrote:

I think what happens is that when the flow of water to the hot tap is suddenly stopped the momentum of the flowing water causes a surge of pressure in the pipework. If the water can go through the pump it activates the pump's flow switch and turns on the pump.
If the shower valve is turned off water shouldn't be able to flow through the pump - it has nowhere to go - but if there's air in the pipework between the pump and the valve the high-pressure surge can push enough water through, compressing the air as it does so, to trigger the pump. Of course there's nowhere for the water to go to continously so the pump only runs momentarily and then stops. (Although under certain circumstances a repetitive pulsing of the pump can occur.)
If your pipework from the pump to the shower goes up and then down again then you have the potential for air to get trapped at the high point of the pipework. Fitting automatic air-bleed valves (e.g. BES part no 7704     BOTTLE AIR VENT 1/2" WITH CHECK VALVE    2.33 + VAT) at the high points may cure the problem.
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wrote:

As noted above this is a problem if there is any air trapped in the hot system.
One way to cure it is to disconnect/remove the switch that senses the hot water flow (these are usually reed switches attached to the outflow) leaving the pump actuated by the cold flow only.
Only effect is that the pump doesn't turn on if valve is set to maximum heat - which is unlikely and probably too hot for comfort anyway.
Chris K
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CJK wrote:

I was going to mention that on some (older? better?) pumps the flow sensor switches are adjustable for sensitivity.
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On Thu, 10 Mar 2005 21:29:38 +0000, John Stumbles wrote:

Or you may have a run of inadequately clipped & supported pipework on the branch to the shower, this moves with the pressure pulse and expands in volume a little but enough to start the pump.
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Thanks for all your suggestions. The trapped air scenario described our symptoms perfectly, so I tried dealing with that first.
The hot feed is taken from the side of the cylinder then vertically to the attic, turns through an elbow and runs across the attic floor to the pump mounted at floor level. There is a bleed valve on the elbow, that yielded a little air but made no difference to the problem.
The hot outlet is mounted on top of the pump, from where a short flexible connector picks up the copper tube at a point slightly higher than the pump outlet. There is then a gradual pipe fall (10 in or so) across the attic floor before dropping vertically to the shower mixer valve. There didn't seem to be a sufficient gradient to form an air pocket, but I tried to bleed the system at that point by cracking open the pump outlet connector with the inlet closed and the pump off. Much water, but not possible to see if any air was released (I know this is not sensible plumbing!). Trying the shower then produced some coughing and hammering, but it all settled down & I ran it for five minutes or so. Since then 24 hours without any sign of the problem.
Not 100% sure of what I did, but if it happens again I can choose between fitting an air vent just downstream of the pump hot outlet or deactivating the hot flow sensor I guess.
After four years of use free of problems, let's hope for another four.....
Many thanks for all your help. Trevor .
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    Consider fitting a non return valve in the output side of the pump. This stops water surges at pump switch off.
    Regards     Capitol
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I had exactly the same problem........fitted a non return valve after the shower punp on the hot water pipe and sorted the problem nicely......... One problem is that the shower may take a while to come on as it is having to push against the force of the non return valve.......this is more noticeable when the valve is brand new and will become less of a problem after a couple of showers (ie two months in my case)
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Maxie, did you read that. Din Lin only had two showers in one month!!! Must stink to high heaven. Appalling.
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