Shower pump not cutting in

[mackandmutley]

I changed the combined thermostat/selector valve on an aqualux shower cubicle which had begun to leak. Since fitting the new one the shower pump is being difficult to cut in when you turn on the selector to either of the heads. Only way it seems is to drop the handheld head out of the holder and on to the floor, forcing the pipe work to dribble out at which point the pump will fire into life,

Any thoughts... Is it the pump ( it's 6 years old) and just a fluke it happened when I changed the valve or is it something else?

 

[stem]

There are two types of shower pump.

Some are suitable for a negative head which means they can be used where the header tank doesn't provide sufficient pressure for any water to flow through the system unaided.

However, from what you say, I suspect that you probably have the most common type which is for a 'positive head'. This means that there needs to be enough pressure to allow a flow of water through the system when the valve is opened before the pump operates (your pump instructions should tell you how to check if the feed tank is high enough or not and what flow rate is required) When the water flows under its own pressure, this operates the switch(es) to start the pump motor. It would appear that you are not getting sufficient flow to operate these switch(es) unit the shower head is lowered.

So the question is why has this happened now the valve has been changed? Possible reasons are:

Is the new thermostat / selector an exact replacement? If not it may be restricting the flow when compared with the original
Are the pumps manual isolation valves full bore and fully open?
If there are filters in the line to the pump and if so they maybe partially blocked?
Have you changed anything else?

 

[mackandmutley]

Thanks for your reply,

To answer the queries:

The new thermostat and selector was bought direct from Aqualux, fitted fine, looked identical and no reason to think it wasnt the same.

Valves are full bore and fully open.

No filters downstream of the pump that I know of unless the shower has them fitted somewhere, upstream feeds to the pump come direct from cylinder, about 2 foot away and seperate cold feed from header tank in loft directly above about 8 foot.

Not changed anything else and hence why i am blaming the selector valve ( maybe a filter/restrictor inside the new one but not in the old one).

When the shower is working all seems fine with pressure etc, just annoying that you have to go through the process of almost having to goad the pump into life by drawing water off from upstream.

 

[andytw]

With the pump turned off do you have a reasonable unpumped flow of hot and cold water.
I recently had a pump fitted and it would not cut in when cold required and when hot was run the mixer valve would turn off with anti-scald feature. The problem was an air-lock in the cold feed pipe.