Salamander Pump slow to start

[Ashtara]

We have had a RSP100 pump installed nearly 4 years ago and has been working fine until the last month when we noticed a reduced flow in one of the showers and a pulsing coming from the pump when it was turned off.

We have now had the valve on the shower replaced and a new NRV fitted to the hot outlet of the pump.

For a week the shower worked fine but lately we have noticed it is taking a few seconds for the pump to kick in when we turn it on.

I have done a bit of research and it seems it may be something to do with the pump not being negative head pump but as it has worked fine for nearly 4 years how can this be?

Could either of the two things we have had done above affected this?

 

[ChrisR]

Yes, the NRV is an extra resistance in the line, so if the head isn't strongly positive then it could stop the flow which would otherwise trigger the pump to start.
If lowering the showerhead makes it start reliably, that'll likely be it.
Less flow - depending on the NRV, possible. Could be dirt though?

You often don't really NEED an NRV on a pump. Can the shower head drop into the tray? What (else) does the pump feed?

 

[Ashtara]

There was already a NRV valve on the pump it was just replaced as had stopped working so how would it be the NRV?

It feeds another shower which is right by the hot water cylinder.

The NRV was replaced to stop the 'ram-rodding' - the pulsing noise when the shower was turned off.