Shower Pump Delivering Unequal Hot and Cold Pressure

29 Oct 2007
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United Kingdom

Can anyone offer any advice on this shower problem please?

Until this weekend I had the following shower setup in our house.

We have two showers, one in the main bathroom upstairs and one in our en-suite (also upstairs). Both are Aqualisa mixer showers fed from a traditional non-pressurised hot water tank on the same floor as the bathrooms and a cold water tank in the loft.

Each shower also uses a twin impeller pump in the loft - the en-suite runs off a Stuart Thomas 2 bar Monsoon pump and the main bathroom off a Salamander Pearl 50 1.5 bar pump. The en-suite is fed via 22mm copper pipes and the main bathroom shower via 15mm plastic pipes.

The en-suite shower has not been used for about a year due to a problem with the tiling which is awaiting fixing.

Earlier this week the Salamander pump for the main bathroom shower started to leak. So, I decided to replumb things a bit so as the main bathroom was fed by the Stuart Thomas Monsoon pump that was originally feeding the en-suite.

This involved running some new 22mm plastic pipe from the Monsoon and then connecting onto the existing 15mm pipework for the main bathroom shower via 22mm to 15mm reducing elbows.

Once I had done all that I tested the shower and found that the Monsoon pump had jammed and was slowly burning out the motor. I opened up the impeller at the cold end and freed it up. Tested it on the bench to prove the motor now worked, and then hooked it back up to the pipework.

It now works fine except for one thing. The pressure on the cold water is quite low - certainly much lower than the hot pressure. It's also not much more than the cold pressure I get if I run the shower with the pump powered off.

The pump is kicking in when I run the shower on fully cold - it's just that it doesn't seem to be pumping as hard as it does when it is on fully hot.

I've run it on max hot and max cold for a while with the shower head on the floor of the shower tray, and with the pump powered off, to try to clear any air in the system.

I've checked the filters in the pump inlets and they are clear. It may be worth noting that I also ran it for a while this morning with no filter in place on the cold side (due to not noticing it had fallen out when I had the pump on the workbench last night).

Any ideas please??

By the way, it seems from reading the Monsoon installation manual that it should not be installed above the height of the HWC. However, it has always been there and always worked fine in the past when it was being used for the en-suite shower.

Thanks in advance for any help.

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Its where the cold water feed tank is located that matters most.

But they are still concerned that it can suck air instead of water down the HW cylinder vent and effectively run dry.

Unfortunately you seem to be muddling up pressure and flow and that gives me some difficulty in understanding what your problem is.

When it's on 100% cold the water comes out of the shower head at a slower rate and hits the shower tray less firmly than when it's on 100% hot - so I guess I'm talking about flow?
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When I opened the impeller housing last night I'd put it back on the wrong way up. Doh!

All working fine now. Hopefully this thread will help someone else out in the future though. :)

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