Shower Pump Starts on its own intermittently

[Sefnot]

Hi -

I had an old watermill low viltage pump that worked great for years. That went so replaced with a new (Grundfos- positive head) from my hot water cylinder. All it does is power my bath/ shower (via one mixer tap).

The issue is that since installation it starts up on its own (without the tap being opened) most mornings (and intermittently throughout the day), making a whirring noise sounds like squeaky air being released.

I have just discovered that the mixer tap (to the bath/shower) is in fact dripping.....The plumber is suggesting that this is the cause so I am changing the tap but will this solve he problem?

 

[Ben-gee]

Yes

 

[John.g]

Are you sure its positive head as these use the flow switches to start & stop them and require ~ 0.5 to 1 LPM to switch, a drip will hardly start it. A negative head pump or universal uses a pressure switch and a drip will certainly start that.

 

[Sefnot]

Yes

Thank you. That's reasssuring.

Are you sure its positive head as these use the flow switches to start & stop them and require ~ 0.5 to 1 LPM to switch, a drip will hardly start it. A negative head pump or universal uses a pressure switch and a drip will certainly start that.

Hi - Thats what I thought.... Its definitely a positive head. Its in a flat - hot water cylinder in cupboard (which plumber also says is too small)

The plumber who fitted the new pump..came back and discovered that he tap was dripping (it is I've seen the video- which unfortunately IT issues mean I cant attach..) ......his view is that the change in pressure due to the leak is starting the pump off.......and Im not convinced but guess I wont know until mixer tap is changed....

 

[John.g]

Can you measure the drip into a bucket for 30 secs or so to give you a flow rate.

Edit: what stops the pump, once the drip has started it?.

 

[Sefnot]

Can you measure the drip into a bucket for 30 secs or so to give you a flow rate.

Edit: what stops the pump, once the drip has started it?.

Hi- unfortunately not as not there...rented..

sometimes there is a drilling sound first but then the whining/squeaky noise.... and then it stops of its own accord.

Thank you

 

[Deleted member 123817]

Is it a "single" ie just boosting the hot water or a "twin", boosting both hot & cold?

 

[Sefnot]

Is it a "single" ie just boosting the hot water or a "twin", boosting both hot & cold?

Hi- twin.

 

[John.g]

Bit strange, both would normally be fed from the same head, the CWST to the cold end and the CWST to the hot end via the HW cylinder, something seems to be moving one of the flow switch floats hi and then low enough to stop/start the pump. Assuming no flow switch problems then just possibly a air pocket building up/collapsing somewhere (hot side?) but this would point to improper installation. Presume hot water temperature not exceeding 60/65C.

 

[Ben-gee]

Are you sure it isn’t also connected to a lavatory?
If a flushval e let’s by (very common) , the inlet valve will open to make up volume- this could trigger the pump.

 

[Sefnot]

Thanks Ben but plumber tells me the pump has its own dedicated feed....and the noise happens early morning before (the only person who lives there) is up and about. Plumber reckons its something like as the pressure is highest in the mornings the drip sets it off then...I'm just hoping replacing the (dripping) mixer tap help.s..

 

[Deleted member 123817]

Ben May be suggesting that the toilet cistern is supplied from the pump cold end discharge I think.

Only way high pressure/more drips in morning is possible is that the mains is connected to the cold end inlet? Except that the header tank is at a higher level

 

[Timmy D]

Flush the toilet, see if the pump starts.

Isolate either the hot or cold inlet at the pump valves over night and see if it resolves the issue. This will focus the fault find on the correct supply.