Shower Pump Problem

[Chrisscotty]

Hi all,

I am currently in the midst of my bathroom replacement and I have come across a problem that I hope you can help me with.

I have installed a new Grundfos Amazon STP-2.0 B regenerative pump. I have a traditional gravity fed system. I have tested the system before I close up and all is working corrrectly and I have no leaks. However when I use hot water from any other taps in the house (not fed by the pump) the pump pulses on and off until the tap is turned off.

Things to note is that I have Tee'd off the hot water supply at the first downward leg from the cylinder. I understood from my research prior to installing the pump that this would be ok aslong as a regerative pump is used, due to being less susceptible to air in the system, hence I have not installed a surrey flange. This would be more difficult and I'd rather leave the connections to the tank alone as its quite an old tank.

I have read that others that have had this problem have installed a non-return valve on the outlet side of the pump. This is also suggested as a solution in the Grundfos manual. Have others come across this problem and has it been resolved via a non-return valve or is a surrey flange really the only way?

Regards,

Chris

 

[Madrab]

The draw off from the other HW outlets is creating a lower pressure in the supply pipe to the pump triggering the flow switch and causing the pump to pulse. Never a great idea to tee off the normal house wide hot supply.

You should always have a dedicated flanged feed to any pump to ensure things like this don't happen.

 

[Chrisscotty]

Hi, thanks for your reply.

I appreciate that it isn't best practice and in hindsight I would do it differently. However, as I now have the problem, would a non-return valve on the hot outlet from the pump fix the issue? I really would rather not touch the cylinder if at all possible. My understanding is that it is the pressure of the water in the vertical pipe from the pump that wants to fall back towards the pump that is causing the issue? I assume that as it is suggested in the troubleshooting page of the manufacturers manual it is a relatively common occurance?

Chris

 

[Madrab]

It can be if there is significant draw on the HW supply, in effect it is trying to suck water through the pump as there is a venturi effect causing a slight vacuum at the tee to the pump.

Usually you don't want valves on the downstream side of the pump but if grundfos allow it then no reason not to try it.

 

[Chrisscotty]

Just to follow up the non-return valve solved the problem for me.