Single impella pump

[88cookie]

Hi,

I’ve installed a single impella neg head bronze pump on hot outlet. It feeds 2 new showers and a few other outlets.

Top floor bathroom not of pump. The system hasn’t been done well before hand and I’m going off what’s there.

Pump is now installed of secondly feed at tank etc, I then found out 2 showers I changed were off mains. Pressure reducing valve and non returns and I’ve sorted the mixing issue so now the showers are regulating as they should.

Now the pump is intermittent. I think it’s air, I’ve piped the pump of secondly outlet, as it should. vent comes off cylinder in 22mm (Does reduce from 28) but that’s how it was. The vent comes off top of tank and also feeds upstairs bathroom then off to vent.

He’s going on holiday, is the pump pulling air? But if I run a tap down stairs pump runs fine, stays on and no issues. Only does it with the showers, sometimes however it works ok. I run the showers through as grundfos recommended and the pump worked. Then starts doing it again? Any help would be appreciated

 

[Madrab]

Is the pump hunting? Not sure what you mean by intermittent, does it start/stop?

Things always get tricky when feeds are not balanced. if the pump is being fed from the 2nd tapping, usually an essex flange, then air shouldn't be an issue, especially if the cylinder is venting up through the top vent pipe.

 

[88cookie]

Yea the pump is stop start. It does get tricky but it’s how the system is and customer is limited. It’s a stainless steel cylinder. Didn’t think you could put an Essex flange on seconds outlet

 

[Madrab]

A second tapping on a cylinder tends to be an essex type, it's designed so it seals to the curved surface of the cylinder. Unless it's manufactured as part of the cylinder and then it would normally be brazed.

If it's an on and off then does it also pulse when it's running? Take the head off the shower and see if it still does it. If that cures it then it's back pressure, if not then it may be due to the supplies not being balanced and the shower valve is fluctuating. Airlocks could be an issue, try mains flushing back up the HW just in case. How hot is the water set at?

 

[88cookie]

it runs then stops then runs then stops. Hot water set to 55 degrees mate. Killing me this one nothing I could have seen before hand unless I could look through walls. I will try those options. Pressure reducing valve set to 2 bar, same as pumps output. Same for both showers. What if it’s back pressure?

 

[Madrab]

Back pressure can be caused by restricted flow - poor/restrictive shower head/hoses - blockages or poor laid out pipe runs causing higher resistance - turbulence causing air bubbles to be created again usually down to poor pipework/fittings.

The HW temp can cause a poorly calibrated TMV/ antiscald to activate - restricting the hot, then it cools and it opens and the cycle repeats. It can become a real head scratcher.

 

[88cookie]

Any advice on what route to take?

 

[HERTS P&D]

Have you checked the float valve in the cold water storage tank? is it running dry?

Andy

 

[Madrab]

Any advice on what route to take?

If it was me I'd start at the beginning and work my way back. Take off the shower head/hose and check (rules that out), then take off the shower and add some pipe to the feeds and a full flow valve and try that (rule out the shower). Then take a direct feed pipe from the pump outlet to the shower and see if that corrects it (rule out the pipework), etc.... Can you create the problem or does it just happen randomly, if it's the latter it'll be harder to trace as you won't know when it's been corrected.

The only other option would be to take it back to a proper design approach, take a cold feed from the cistern and fit a dual pump. mixed/unbalanced supplies can be troublesome when it comes to showers.

Edited for poor grammer