Shower pump problems

Hi

I have recently plumbed in a salamander rt50 1.5bar pump. Because I can't alter existing pipework it has to operate not only the shower but the kitchen hot tap & basin hot tap. Pump is in loft over a meter below cold tank. Have taken hot feed off top of cylinder & cut pipe feeding rest of house lower down & elbowed into that. Cold is straight forward. All worked well then 3 days in shower only works when a hot tap is turned on at same time. 

Any ideas please

Cheers

are you pumping the cold too? could be lack of flow to start it

You have trapped air in a pipe by opening the hot tap you are creating a release for air to travel thus allowing flow of water. 

So you have a vented hot water cylinder  which is below the pump, and the water has to flow upwards to the pump then down to the shower and taps?  

(Have I got that right?)   

If so I suspect that air from the cylinder is going into the loop so formed instead of going up the "expansion" vent. Think of a syphon with an air bubble in it.

The shower then doesn't  have enough pull to break that airlock, but when a tap is opened lower down the water remaining in the pipe to that tap will pull through a supply to switch on the pump flow sensor.   (Only a guess but I would almost bet on it)

The best fix is to relocate the pump below the top of the HWC. 

I would have thought you should have amended the connection at the top of your water cylinder. You can't just branch off the standard hot water pipe without getting continual air pocket issues. That's why I thought they make these.  https://www.screwfix.com/p/salamander-pumps-s-tank-flange-fitting-for-hot-water-cylinder-22mm/76906

Doc H.