Shower Hot Water Pump not activating...unless you turn the sink tap on!

[dnasewell]

Hi there!

We've had a bathroom installed with a new shower.

We have a gravity fed hot water system - Not a combi boiler system. We wanted good pressure and were recommended by the fitter to opt for a pump for the hot water and a timer on the immersion heater in the tank to come on in the morning to give us enough hot water.

We installed a pump for the shower at floor level below the thermostatic mixer, which is at about chest height, which feeds a rainhead and a separate handheld hose.

The problem is that when you turn the shower on it merely drips and the pump doesn't activate. If you turn the shower all the way to cold then the cold water flows. If you turn it quickly from cold to hot then the pump kicks in and you can have a shower!

I thought it might be a problem with the thermostatic mixer cartridge so I got a replacement sent but the problem is still the same.

Any ideas?

There's some more information to give you the bigger picture that might help...

We installed a 2 basin sink unit with a mixer tap for each basin. The hot water flow on these was really low and after contacting the seller we found out that the mixer taps needed a high pressure input...we needed another pump for these taps! Unfortunately we only discovered this after the bathroom floor had been laid.

So we installed the pump in the utility room under the bathroom floor for the taps which solved that problem and these taps work fine - no problems there.

This left us with 2 pumps feeding the shower hot water feed! The original pump installed below the thermostatic mixer has an isolator switch and so I've turned this off as with it on the shower is like a pressure washer and empties the tank too quickly!

I discovered another way of turning the shower on: Turn it on - no flow, only dripping...turn on the mixer tap for the basin...the pump fires up and the shower works!

It's useable at the moment but annoying and I'd like it to work as it should.

I'd be really grateful for any advice of anything I can install or re-jig in the system to resolve this.

Our feeder tank in the loft is elevated on legs about 1.5 metres up in the air.

I'm guessing it's a problem with water pressure no being sufficient to activate the flow switch in the water pump unless syphoned by the cold water flow. Is there a way of increasing the water pressure in the system? I'm guessing not, without changing the system for a pressurised system and I'd rather not spend thousands sorting this.

Thanks in advance for any advice you have.

Danny
York, UK

 

[SimonG]

So hots gravity pumped and cold is mains. If so then your fitter is a bell end.

 

[lame plumber]

basically your whole system is wrong, cylender is too small to cope with a large shower head, mains/pump fed system being intermixed and then putting a second pump on an already poor system!! Get in a decent plumber and look at having an unvented cylinder installed if possible to save grief in the long term

 

[dnasewell]

The hot's always been gravity fed and the cold's always been mains pressure...The cold water pressure has always been good. We opted for a single pump for the hot water as we didn't need the power boost for the cold water. How would you fix it? Thanks Simon, D

 

[lame plumber]

unvented cyl with a balancing valve so the shower works and has enough hot water

 

[SimonG]

Either twin impellor pump and new tanked cold feed. Or unvented cylinder if your mains flow and pressures are acceptable. I would prefer the latter.

 

[dnasewell]

Thanks!
So do you think replacing the single hot water pump with a dual pump for hot and cold would sort it?

 

[SimonG]

As long as the cold is taken from the tank.

 

[dnasewell]

Right, so you couldn't have mains cold and gravity fed hot going into a twin pump?

 

[SimonG]

No. Tanked cold with the gravity hot will give a great shower with a pump. Might need to look at quantity of stored water though.

 

[dnasewell]

Forgive my ignorance...one thing I don't understand is why our sinks work fine and can activate the hot water pump but the shower can't. It's the same pipes and same pump. I suspected the thermostatic mixer function on the shower might have had some affect but I don't know... I remember the fitter put a non return valve in before the shower mixer...would that have affected it?

 

[SimonG]

The mains cold is stopping the initial flow of the hot so not kicking in the flow switch on the pump.

 

[lame plumber]

but still there is an issue of a pumped drench shower on a small cyl........................