Lack of shower performance after replacing pump

[divingscubaboy]

Hi All,

I have recently replaced a shower pump for a family member and now it is a struggle to get a decent shower.
The original pump (nameless no ID plate etc) had been working absolutely fine supplying 2 showers without issue.
Since fitting the new pump which is a watermill and suitable for 2 outlets there is practically no flow when the heat is set high. If the shower is started on a colder setting there is a slight improvement. It sounds very much as though the pump cavitates when first activated. The plumbing has not been altered so find it difficult to see how the original installation can be at fault.
I am suspicious that the hot supply is draining back and that neither shower has non return valves. Would fitting a non return valves to the hold and cold at each shower or before the pump aid in keeping the pump full of water when activated preventing cavitation?
Any advice greatly received. Thanks

 

[Richard C]

I have recently replaced a shower pump for a family member and now it is a struggle to get a decent shower. The original pump (nameless no ID plate etc) had been working absolutely fine supplying 2 showers without issue.

Have you replaced the pump with another of similar performance? Is it a negative or positive head installation? Where is the pump located in relation to the HW/CW storage tanks?

Since fitting the new pump which is a watermill and suitable for 2 outlets there is practically no flow when the heat is set high. If the shower is started on a colder setting there is a slight improvement. It sounds very much as though the pump cavitates when first activated.

I’m assuming the flow switches are activating as you can hear the pump; it sounds like the pump may be air locking, did you bleed water through the new pump before finally tightening the connections?

The plumbing has not been altered so find it difficult to see how the original installation can be at fault.

Not necessarily, is the HW cylinder take off via an anti-aeration flange? Is there any up & over pipe work from the pump to the shower head?

I am suspicious that the hot supply is draining back and that neither shower has non return valves. Would fitting a non return valves to the hold and cold at each shower or before the pump aid in keeping the pump full of water when activated preventing cavitation?

The pump should always be full of water if the system is correctly piped & the pump has been bled on installation, if it’s not it won’t last long! You only ever need non return valves in very specific instances & they must NEVER be fitted on the pump feed side i.e. between the HW cylinder & the pump.